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Persistent Rough Idle & Driveability Issue

10K views 33 replies 8 participants last post by  rhandwor 
#1 ·
Hey everyone!!

I've had a 2004 Kia Sorento EX for about two years now, and I've had a persistent [and extremely frustrating] issue, and I'm really hoping that someone here can help me out.

I purchased the SUV from a private seller, who'd literally let it sit in his driveway for 6 months. He purportedly just never got around to selling it, but I now understand the REAL reason why. From almost the beginning, I've had one issue after another - and to date, I've spent roughly $4,000 in repairs and replacements. At this stage, a majority of the components in my engine compartment are brand new, but I still have this lingering, persistent rough idle, piss poor acceleration and engine stumble at high speeds.

It FEELS like a misfire, because that would likely explain all of these symptoms. Cruising, the engine is fine, runs beautifully. But, when I accelerate from a stop light, there's a slight stumble, that kinda feels like the engine is tripping over itself trying to move. Then, once I'm moving, shift timing is way off. It also feels like a lean or rich condition, hard to tell, because the gas pedal can tend to have a "spongy" feeling...where there's not as much pressure behind the throttle as there should be. Good lord, I hope I don't sound like a complete idiot trying to describe this :p

Here is a complete list of all the replacements, repairs and services I've had over the past two years:

[2012] 07.17 - New NGK Spark Plugs
[2012] 07.18 - New Tires
[2014] 07.20 - New Throttle Position Sensor
[2014] 07.24 - New In-Tank Air Filter [Warranty Item]
[2014] 07.27 - TPS Adjustment
[2014] 08.29 - New Driveshaft
[2014] 08.29 - Exhaust Manifold Leak
[2013] 01.23 - New Fuel Filter
[2013] 02.19 - Cleaning of Mass Airflow Sensor
[2013] 02.25 - Cleaning of Throttle Body and Air Intake
[2013] 04.02 - Replacement of Power Steering Hi-Pressure Host
[2013] 06.27 - New Idle Air Control Valve
[2013] 09.09 - New Fuel Pump
[2013] 09.30 - New Oxygen Sensor [Upstream]
[2013] 10.04 - New Oxygen Sensor [Downstream]
[2013] 10.04 - Complete Fuel System Cleaning Service
[2013] 10.23 - Transmission Flush
[2014] 02.03 - New Engine Air Filter
[2014] 02.03 - ANOTHER Complete Air Intake Cleaning Service
[2014] 04.14 - New Timing Belt
[2014] 04.24 - A/C Service
[2014] 05.05 - Replacement of Transmission Mount
[2014] 05.22 - New Engine Coils
[2014] 05.27 - New Battery
[2014] 05.30 - New Spark Plug Wires

Needless to say, I am at a TOTAL loss with this car. I've tried very hard to take good care of it, but it has become a living nightmare. No codes, so my mechanic is at a total loss. And after every major service, I always reset the ECU by unplugging the battery. So, I have no idea what else to look for. Does anyone have any ideas? I'm open for suggestions!! Thanks everyone :)
 
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#8 ·
@windsboy - THANKS!! sweet deal. so, my mechanic pulled out my plugs and they're super clean and still look new, since i just changed them less than 8,000 miles ago. coils and spark plug wires are also new.

i'm gonna let him hang onto it for a few days and see if he can figure out what's going on with it. the other day, my engine cooling fan decided to stay on all day and night, so my brand new battery - which i literally bought two weeks ago - is dead. nice. so, once i jump it, i'm gonna drive to his garage and drop it off.

in any case, do u guys have ANY ideas as to what he should be looking at? we've done a compression test, the plugs/coils/wires are good, no indication of a vacuum leak, throttle body and air intake system has been cleaned about a dozen times, nothing's unplugged, brand new fuel pump/filter inside the tank, idle air control valve was recently cleaned...again.

so, at this stage, we are completely at a loss. i've spent SO MUCH MONEY in this car, and but for this stupid vibration, shudder, stumble, hesitation issue, it looks like a brand new ride. at idle, it shakes HARD. clearly, this thing is misfiring BIG TIME!!

for next week, he plans to check: the connection between the throttle position sensor and the ECU, the fuel pressure relay, inspection for any bent valves, and examine all of my wires and harnesses. but do u guys have ANY other suggestions? it'd be greatly, hugely appreciated!!!
 
#11 ·
so, at this stage, we are completely at a loss. i've spent SO MUCH MONEY in this car, and but for this stupid vibration, shudder, stumble, hesitation issue, it looks like a brand new ride. at idle, it shakes HARD. clearly, this thing is misfiring BIG TIME!!
+1 on compression test, leak-down test, and visual inspection of timing components and mating marks to verify mechanical timing is correct..

re: cooling system - would recommend a coolant system pressure test, if at all suspect, during the mechanic's inspection..

Your cooling system issue sounds suspicious - I would verify engine / mechanical integrity, to rule out a more serious issue related to above as the reason the original owner 'parked' it before sale..

--
If it was 'my ride', I would not 'throw more parts' at the motor until I verified basic mechanical integrity and compression on the motor..

I know this is not what you want to hear - but I hope the advise helps,
Regards, GottaCruise
 
#10 ·
If your engine is overheating this will make them run bad. Did you pull the vacuum hose on the pressure regulator? These will definately make them run bad.
Did you run the engine with a good scanner and monitor the system it appears your spending tons of money without finding the problem.
Otherwise I would upgrade your ride.
 
#12 ·
@GottaCruise - thanks for the advice! and no, i don't really take that attitude. i'm always grateful and appreciative when someone shares their honest advice with me, because i've tried literally everything u can imagine, and it helps to have any new direction to take :)

as for the engine cooling issue, we determined that it was a relay switch that needed replacing. i tried to jump the Sorento yesterday - just to see if i could get it running and, hopefully, recharge the battery a bit. but the very second i connected the last negative clamp onto the body of the truck, the fan started running immediately. took it off, the fan turned off. hooked it back on, the fan turned back on. and this was around 8am, with the engine ice cold. so, we now know that it's unrelated to the engine temperature, and just a relay that needs replacing. also, it's just the smaller fan, on the bottom - not the larger, main fan on top. lol.

and as for compression, vacuum and leak tests - he's connected a scanner to a vehicle and ran every possible test he can think of, but everything still "looked" fine. there was, however, a CLEAR issue when he disabled certain cylinders. for example, he disabled 2,4 and 6 and saw that the misfire is DEFINITELY taking place on the bank which houses cylinders 1,3 and 5. so, we're a little bit closer.

otherwise, i'll ask him to check the furl pressure regulator in the morning. but i also read something about a recall for ICV screws coming loose and becoming lodged in the valves. anyone heard about this? there was some information about this possibly causing a misfire. and also, i found another thread where someone said there's sometimes an issue with the connection between the TPS and the ECU. something about "false readings", possibly.
 
#14 ·
HEY!! finally...finally...FINALLY found the answer!!

i left the sorento with my mechanic last monday and told him to take his time. when i dropped it off, it was misfiring so badly, it felt like it wanted to stall. i mean...the entire car was shaking violently. it was a nightmare. well, i just received his call this evening, telling me that i could come and pick it up.

i'm very good friends with his wife, so as soon as i got there, she started telling me about how obsessive he'd become about trying to find the solution. he committed atleast two hours, every night after he closed his shop, to figuring it out. she said he would get home late, and then still stay up on the computer, relentlessly searching TSB's, online forums, techincal websites, the whole nine yards.

he said he ran every test he could think of, examined the entire car from top to bottom, front to back - and eventually made up his mind that the ICV inspection would be his final try. he looked up the info for the recall and took apart the entire manifold, but saw that the entire upper intake was virtually brand new and everything was beautiful. so, he was gonna throw it back on, bolt it up and call it a day...but, for some strange reason, he had a hunch to check the spark plugs. he said it was weird, because he'd just changed them himself, only 5k miles ago - so there was no real reason why he'd need, or want, to reinspect them.

nonetheless, he pulled them and saw that they were BURNT BLACK. totally covered with black soot. they were NGK's, so he couldn't quite understand what went wrong. so, he called kia and talked to someone long enough to find out they strongly recommend OEM plugs - which are $20 a piece - for this truck. he ordered six from our local dealership, popped them in, and the sorento drove like a brand new car!! idle was buttery smooth, INSTANT throttle response, shifts were perfect, no hesitation, no stumble, no odd noises. plus, since i've replaced pretty much every other major component on and in the engine, AND did thorough cleanings of the intake, throttle body and MAF sensor...this thing ROCKS the freeway now!! i honestly did not wanna come home, because i couldn't believe how amazing this car felt. it was like driving it for the very first time!!

and @GottaCruise - yes, i am so honored and grateful to have met this man. he has become a very trusted and dear friend, and he's been wonderfully patient and persistent with my car. and the best part? he wouldn't charge me a single dime for the new plugs!! he told me that, after two LONG years of having my car in and out of his shop, it became really personal for him and he found himself obsessed with trying to find the solution. i could keep myself from crying, but it was truly amazing.

so - i hope this helps someone else out there!! i know a lot of pplp use NGK and champion plugs without issue...but for some reason, my car simply DID NOT like those NGK's!! lol. and as for now, i'm thrilled to finally...FINALLY...have my car running like it should :)

 
#15 ·
NGKs or Densos are the OEM plugs for these cars and they should perform properly..."IF" the correct types are used... I would think your "problem" will come back fairly soon if the plugs didn't really solve the problem....

Have you checked the primary/upstream catalytic converter for blockage? You may have a problem with back pressure on that head... What is the actual mileage on the car?

I hope that the plugs WERE the problem but unless the type was totally wrong I think the problem may come back... What brand and type plugs where installed?
Dave
 
#18 ·
hi :) while i certainly respect and appreciate everyone's input, i'm absolutely certain that the plugs were directly involved with the misfire issue. today, i drove for about 3 hours - on the freeway and around town - and the car drove better than it has in the entire 2 years i've owned it. it feels like it's RIGHT on the edge of perfection...like there's just one minor thing keeping it from being truly great.

so, we're guessing that the generic aftermarket coils and ignition wires that i bought from eBay might not be producing a high enough voltage to sustain or transmit a proper spark to the new plugs. THANKFULLY, i kept the denso OEM coils and wires that he took out, so i'll be going back tomorrow morning for him to re-install them. as of right now, there is just a slight [but noticeable] misfire vibration at idle and high-level acceleration [like merging onto the freeway or making passing maneuvers] produces excellent power, but the downshifts aren't as perfectly timed or as smooth as they should be. but those are the only two remaining issues. otherwise, it's nearly there!!

my mechanic had already installed the new "kia" plugs by the time i got there, so all i saw were the boxes and the old plugs. but the photograph on the boxes did show a plug with a "kia" stamp, so they do appear to be "factory" made. and as for the catalytic converter, he'd already removed and inspected that, too. still looks clean and no signs of clogging.

so, i'm pretty sure we've arrived at our solution. but thanks again everyone!! ur suggestions and advice has been invaluable to me. you're all amazing :)
 
#19 ·
You keep doing the same thing throwing parts. Seriously six new coils not firing properly.
Your fuel mixture is to rich. On older cars carburetor adjustment,mechanical fuel injection out of adjustment. Especially Chevrolet bad pressure regulators will cause this. The fuel will flow through a ruptured diaphragm get into the intake and cause rich fuel mixture..
The computer can only adjust the mixture if other parts are good.
 
#21 · (Edited)
If you suspect Ignition wire issue to the back bank, if it was me, I would just (replace) the wires with (new) OEM Denso or NGK wires -

sound advise given to me years ago was to -never- re-use old wires or plugs when an Ignition issue is suspect, because if you continue to (swap) old parts vs. new, you really can't pinpoint the problem..

Heat, and vibration, kill Ignition wires. Firing an Ignition wire on a bad plug will quickly kill that wire.

The (original wires) suffered the same treatment as the current set on the vehicle. New plugs have mostly solved the misfire issue, highly recommend spending the $$$ for a new wire set. And Ignition coil Boots for the Coil Packs.

OEM Denso's are great, I use and like NGK Ignition wire sets here.

ACDELCO also makes a great (OEM equivalent) wire set - rockauto.com has excellent prices on wires for your Sorento.

Edit: and would check amazon.com also. I would buy from a site that offers a warranty for parts, eBay would not be (my) first choice here, because you can get the replacement parts you need for just a few $$$ more with warranty..

Glad to hear it's almost fixed!

Regards,
GottaCruise
 
#22 ·
I wonder if wiring the bank 2 sensor 1 might be an issue. If the signal wire were somehow grounded or the pcm reads wrong it would increase pulse time for the injectors. I don't think a misfire would occur on so many cylinders at once and there be several culprits. Usually it's just one part or human that ends up causing the issues. Watch the pin to the signal wire from the o2 be pushed out of the pigtail. HA. That would be the type of thing I would look for. But plugs that show signs of running rich are not bad plugs. replace them if it makes you feel better, but they'll clean up quickly once the actual problem is resolved. just remember this...a plug with soot is still igniting, a plug with raw fuel is the one failing to fire.
 
#23 ·
UPDATE!!! hey everyone!! i finally...FINALLY...got down to the bottom of my issue!!

so, after changing the ignition wires - from the cheap ebay set to a very high quality denso set - my sorento STILL had the hesitation, stumble, misfire, vibration at idle, and all the rest.

oddly, my mother recently had a dream about my car, and in the dream, she sad that she told me that the problem was "in my gas tank". that's weird, i thought. but once i started researching, i finally discovered the problem...and it blew me away.

back in september of 2012, i bought a replacement fuel pump from an ebay seller by the name of "global automotive". it was purportedly an "AC DELCO" pump, and i paid roughly $26 for it. after it was installed, i still had all of my symptoms...but i just figured it was something in my engine compartment, like new spark plugs or coils, and never second guessed the pump. well, after my mom's dream, i began reading about how many aftermarket fuel pumps, especially those sold on ebay, are fakes. so, i decided to do a little bit of research on this seller.

it turns out that there are DOZENS of complaints about this ebay seller. they are notorious for selling fake and counterfeit fuel pumps and other aftermarket parts, and almost ALL of the parts they sell end up failing, falling apart, or causing more problems for ppl. but what's really odd is that they have a 99% seller rating. anyway, the way they do this is to state, in their ad, that the parts come with all of the documents and install kits...just no package. so what i received was a pump, an "AC DELCO" manual, and all of the installation materials i needed, but they were all packaged in a generic brown box. and my mechanic installed it, so i can't even recall whether there were any markings or logos on the pump. so, i'm now convinced that the pump they sold me was a counterfeit, too, and THIS is the reason i've had this PERSISTENT headache after replacing every possible component in, on and around my engine.

THANKFULLY, i managed to find an authentic bona fide walbro pump online [GSS342], that i'll be installing on wednesday...so i'm HOPING that it works. good lord, this has been a complete nightmare.

is it difficult to change the fuel pump on this vehicle? i don't wanna pay another $75 to have my mechanic do it again, so i'm gonna give it a crack myself. i know it can be accessed via the back seat - but can anyone give me a few pointers? thanks so much you guys!!!
 
#24 · (Edited)
I would use a fuel pump tester a pressure gage and check the pressure it must be running high to smoke your plugs.
Advance Auto and Auto Zone has loaner tools. A schrader valve is located at the back of the engine fuel rail. 46.9 psi to 48.3 psi with the vacuum hose disconnected on the pressure regulator. With the fuel pressure regulator connected it should be 38 psi. While I think your mother's dream means the fuel system. The schrader valve sits on a short flange with a plastic cap like a air conditioning port. The fuel pressure regulator sits on the other side fuel rail. Google stockwise 1950865 Its possible the pump puts out more pressure than the regulator can handle but I doubt this. Google this site for fuel pump instructions.
 
#26 ·
ok - so quick update :)

following the new fuel pump, things got better for a while...but eventually, the vibration at idle and hesitation came back. so, i just dealt with it and figured i'd just settle for what it is, because i had tried EVERYTHING to fix it, to no avail.

anyway, last week, i did some basic maintenance on the engine. i cleaned the throttle body, idle air control valve and mass airflow sensor, then i checked all my hoses and tubes - and all were fine, and finally, i cleaned the MAP sensor, which is on the intake manifold itself. i reset the ECU, by unplugging the battery, and noticed that the car had A LOT more power than before. however, this pesky rough idle, hesitation and inappropriate shift timing came back with a vengeance!! it was really pronounced now, much more than usual.

so, in complete frustration, i started digging thru all my old service records - looking to see whether i missed something - and i think i've found something interesting. back in 2012, a month after i got the car, my check engine light came on. i took it to a local garage, which i now know is REALLY shady, but at that time i didn't know any better. anyway, they did a diagnostic and told me that my TPS needed to be changed. i paid them about $250 and it was done. but one week later, i got another check engine light - and my local kia dealership told me that it was for another malfunctioning TPS. so, i went back to the shady garage [again, not knowing they were shady back then], and demanded they adjust it. they claimed they did, and the CEL never came back on after i left there - but the vehicle never drove quite like it should either.

so, i'm thinking one of two things: a) they never replaced my TPS and just said they did. [likely, they tinkered with it just enough to get it working again], or b) they bought a really cheap aftermarket piece from somewhere and the low quality is causing my issues. either way, i'm almost 100% certain it's my TPS, and THAT would explain ALL of the issues i've been having all this time - even after changing the fuel pump. my car is just on the verge of perfection at this point. there is just something holding it back from being everything it could be...and i hope that makes sense. lol. something is just a bit off, and i'm thinking this faulty TPS is causing the fuel/air mixture to get all screwed up. plus, for it to be so pronounced after cleaning all of my air intake sensors speaks volumes. all this new airflow must be confusing the hell out of it, and it's causing things to go haywire. lol.

so, for everyone out there...do you think the TPS could be my problem here? again, i've replaced EVERY SINGLE POSSIBLE component, sensor and hose on this engine, plus the TB, the valves, the IACV, the MAF and the MAP are all sparkling clean. new air filter, too. no vacuum leaks. my PCV was changed just two years ago. me thinks the TPS needs to go, and i should find an OEM TPS and stick it on!!

thanks you guys. all ur help is appreciated!! it's gonna be summer soon, and i'm itching to get on the open road, so i'm hoping to get this FIGURED OUT before then. lol.
 
#28 ·
hey everyone!! question...

if the TPS is properly adjusted, but was installed incorrectly, will that affect driveability? for example, if the voltage is set properly and it's giving proper readings, but the mechanic didn't place it back onto the throttle body in the exact position the old one was in...would that have any affect on timing, throttle, etc.? as i understand it, there are oblong shaped holes in the TPS, to ensure proper mounting to the TB, and the objective is to mark the exact spot so that you can adjust it correctly. this is what i'm referring to.

thanks. just trying to figure something out :)
 
#29 ·
@rhandwor: i'd like to, but i don't know how to access the plugs. my mechanic changed them...and i'm not sure i can afford for him to take the entire manifold and intake apart again unless he's changing them a third time. haha!!

but the ones i have should be perfect. he just replaced them about 500 miles ago :)
 
#30 ·
I just thought they were covered with soot as I think you never fixed the original problem. When this is fixed you problems will be over. My vehicle just has a metal cover over the plugs the other job is installing coils and plug wires as the wires go around back of the engine.
I would go to Advanced or Auto Zone and rent a pressure gauge free if returned. The schrader valve has a plastic cap like a tire valve stem. Screw the pressure gause on and check the pressure. A 30 Minute job.
At the back of the engine are two fuel rails the passenger side has a fuel pressure regulator. The drivers side has a spool piece about 3 or 4 inches long. with the fitting on it. This is where you check fuel pressure.
I a lot more experienced on US vehicles and pressure regulators are a frequent problem. The diaphram gets a small leak and gas is drawn into the intake by vacuum which makes the mixture rich and caused idle problems. I've replaced them and the problems went away.
 
#32 ·
@kevinskia: i completely agree with you, buddy. the only problem, however, is that i took out a title loan, with my bank, in order to pay for my law school tuition this year - so, until the bank gets all their money back, it's theirs and i can't sell it.

the good news, though, is that i've ultimately replaced everything on the car, short of the engine itself - and this final fix SEEMS to be the only remaining issue. little by little, the symptoms have started to disappear, and the TPS adjustment appears to make complete sense. AND after i spoke with a rep at my local kia dealership, they confirmed that installing a new TPS requires software and tools that only they have - specifically, the "kia global diagnostic" program, or something like that, to reset the base idle and all the rest.

so, the long and short of it is that i'm gonna be driving this car for a few years. and i've otherwise babied it, in nearly every way, so it's in immaculate condition and looks like a brand new car. ppl ask me all the time how i keep it looking so nice. now...if only i can get it to drive like that...lol.
 
#33 ·
FIXED AT LAST, FIXED AT LAST...THANK GOD ALMIGHTY, MY CAR IS FIXED AT LAST!!

lol. hey everybody - i am THRILLED to say that my sorento is FINALLY fixed, for good!!! after all of the drama, and the repairs, and the replacements, and the constant frustration, and the headaches, and the THOUSANDS OF DOLLARS spent on trying to fix this issue, it turned out to be...my throttle position sensor.

two years ago, i had it replaced at a local auto garage, and i paid almost $300. but what no one ever bothered telling me was that the vehicle would have to undergo a "re-flash" and the TPS would have to be adjusted using "kia-specific" diagnostic software [or, in other words, a program that only kia factory-approved service centers have access to]. so, when the garage replaced the TPS, they apparently just slapped it on and called it a day. anyway, the kia dealership charged me $150 [OUCH!!!] and asked to keep the car all day, which i agreed to. so, once i picked it up in the late evening, i noticed that there was a little difference, but not much. the rough idle and hesitation was still there, but not as dramatic as before.

well, the next morning, i warmed up the car and unplugged the battery for a while. after i started up the engine...it ran like a brand spanking new car. i drove for about two hours after that, and i spent the entire time in absolute disbelief. i had no dream that this car was capable of driving this good!! but keep in mind, i've replaced everything on the car anyway - so, with the TPS working properly, it runs absolutely perfectly now! and the guys at kia showed me a document stating that the TPS values, when i brought the car in, were WAY off...and that's the reason for the rough idle, hesitation, weak throttle and all the rest.

so - finally, some good news!! and just in time for the summer, too!! looks like it's time to hit the road, baby!! YAY!!!

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