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idle problem while moving in neutral

7K views 30 replies 12 participants last post by  ron1004 
#1 ·
When my 98 Kia Sportage MT is in neutral and I am coasting the car idles rough as if it's about to stall. After I stop idles is smooth. When I disconnect the speed sensor the problem stops. This will happen if I am moving in neutral just slightly, like the coast to stop at a light (1mph). I have replaced MAF, IAC, Fuel Pump and fuel pr. Anybody seen this or know how to resolve?
 
#3 ·
My 2001 5spd manual 4x4 sportage was doing something very similar. When rolling in neutral, the idle would always run high, around 1500rpm or so, until I made a complete stop, then it would settle down. Although it wasn't running rough, the solution to my problem was simply repairing a small vacuum leak. The vacuum line running the front hubs broke off the back of the manifold. Replaced the line and it now runs great again.
Check for vacuum leaks perhaps?

I believe what's happening is that the ECU sends a little extra fuel to the injectors when the vehicle is moving. This helps drive-ability when driving/idling in gear. But then again, I'm not a trained mechanic...
 
#5 ·
ECU for sure

I am not sure about vacuum leak but it is obvious from your post and mine that the ECU is doing something just because the wheels are moving. I am not sure why regular idle is not sufficient when the wheels are moving though. Any ideas? Thanks for the post!
 
#6 ·
this is indeed the case. I have not solved this, or started looking for vaccuum leaks yet, been taking care of a few small other things. but I have noticed that it will idle high while rolling in neutral and will not drop down to proper idle until at a complete stop. and if im on a hill and let the vehicle start rolling from a stop, the idle will rise again. so what is the vehicle doing while the wheels are rolling if youre not in gear?
 
#10 ·
I will inspect them when I do my valve cover, but this symptom of high idle is ONLY when the wheels are rolling, in neutral so the engine is idling. When I come to a stop the idle settles down to normal, but if the wheels start rolling again, even without using the motor, just leaving the trans in neutral and let the vehicle start rolling down a hill and the idle will come up to around 1100-1200 rpms. Im not sure if a bad camshaft sensor problem would occur ONLY when the wheels are moving...
 
#14 ·
Have been ruminating on this all night...

Is this issue related to you applying the brake?

Have you monitored manifold vacuum during the situation??

Have you monitored the fuel/air ratio during these events??

During these events, what is the status and voltage on the B1S1?? (Lean/rich, switching/not)

.... Philip
 
#15 ·
VSS = vehicle speed sensor? -- I havent checked

Issue does not change with braking. I can pop it out of gear and roll to a stop and the engine will idle high until the wheels stop rolling then it immediately drops to normal idle.

I have not monitored during high idle but I will and report back.
 
#16 ·
Hi Philip & tspot,

This behavior is normal - the ECM will send extra fuel and/or adjust the IAC valve, if it senses the vehicle is moving to keep idle up until the vehicle stops -> the ECM does not detect movement on the VSS sensor.

Both the Sportages here do the same thing - on mine (Fed. Emissons) idle is approx. 1,500 rolling in neutral until stop, the other (Cal. Emissions) is approx. 1,300 rolling in neutral until stop.

FYI & Regards,
Robert
 
#18 ·
I think the reason the ECM commands fuel / higher idle when coasting in Neutral is to allow for a clutch start, with Key On, Engine Off, ie: 'popping the clutch' - (VSS related)

It could also be MAF related / ECM detecting airflow while coasting, that may be raising the RPMs -> commanding fuel with Key On, Engine On,

re: higher idle, given that both Sportages have the mechanical fan clutch removed & replaced w/ electric fan, that may account for (some of) the higher rpm observed here, I suspect..

When in gear, and coasting, the ECM does cut fuel to the injectors (via TPS) as expected,

Have noted this behavior on (3) different Sportages here, all 5 spd. manual, all 4x4.

Regards,
Robert
 
#19 ·
Mine does this too!

Bump! old post -

Hey everybody, it's been awhile!
Back in the day I was registered here under a different name but had to re-register.

Anyway, yes, I'm still driving my good 'ol 2001 Kia Sportage which I bought new and have maintained myself. 300K+ miles.
I am not the original poster of this thread, but my car does the very same thing too.

It is not a normal condition, it started about a year ago and I've tried everything I can think of to diagnose it. Sure, the idle speed goes up a bit when the car rolls forward, but it's not supposed to go this high!

I've inspected for vacuum leaks, replaced the IAC, the PVC valve, cleaned the mass air sensor then replaced it, but put the original back in as the replacement made things worse.

This car has the mechanical clutch on the fan. Manual tranny. Base model, no AC or anything. It is a 4x4 but I blew the original hubs long ago and installed manual hubs, capping the vacuum line at the manifold.

I know it's old, but if possible I'd like to keep it on the road till the doors fall off! I can't afford a replacement.
Thanks in advance for any tips y'all might be able to provide.

I'm thinking - check the compression? can this simply be a symptom of a worn out engine?
I have not checked the coolant sensor or TPS, don't reckon they might cause this. Does kinda behave like a vacuum leak.
 
#21 ·
I replaced the cam sensor, and it got worse. It only did it with the AC on.
The crank sensor tells the computer how fast the engine is running so that's next. Then the chassis speed sensor. Of course though the obvious is to do a thorough search for a vacuum leak.
 
#22 ·
I did hook up an OBD11 scanner, and drop the idle down. It was at 12.2 %.
The lowest it would go was 11.4% without the screw touching the tab.
I brought it up to11.8%, However there was play in the throttle pedal, but it's only noticeable when driving, which I found odd.
Suprisingly the engine became quiter with an increase in acceleration and smoothness. Not a huge amount but noticeable. It also leveled out at a steady 800 rpm. It was slightly higher before. I'm keeping a wrench handy, and keep making tiny adjustments after driving to zero in on the exact spot where the play is gone.
With no Scanner a good starting point 1/2 turn after the screw touches the tab. The drive it and make small adjustments until the play in the pedal is gone. Stop there.
My 2001 Sportage runs like a champ.
 
#23 ·
Cheap electronics replacement parts can really screw you up. Been there done that. Bought a cheap IAC valve online then spent months, or more looking everywhere else for the problem. Then one day I checked it with an ohm meter. Dang thing never worked right from the start. Pep boys has Bosche parts that match OEM. Saved money and have a choice online at Rock Auto too.
 
#24 ·
#30 ·
My Sportage did all that weird Idling stuff. It was a cheap IAC I installed. Then I was able to adjust the Idle. Once in a while it has a quick drop in throttle, but it runs like a car should.
Also you should always disconnect the battery when you change anything, and allow a few days and miles for the ECM to re-learn.
 
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