Engine dies at idle - Kia Forum
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post #1 of 3 (permalink) Old 09-29-2011, 12:49 AM Thread Starter
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Engine dies at idle

First off I would like to say hello to everyone, I actually frequent these forums and it has given me a plethera of good information to keep my car running strong and up to 180k miles (I'm going to run her till the wheels fall off)

Now to business, as the title says the engine won't idle anymore. There are no power issues as the last night that I drove the car, I had it doing 80 on the interstate just fine. As soon as I slow down, the RPM needle hangs around 500 as opposed to 750-800 and the engine conflicts with itself to run then dies out.

I tried to do my homework, as to most this points out to is the IAC Valve, I removed it and saw alot of carbon build up so the next day I purchased a new one (all the junkyards here were picked of them unfortunately even on hyundai's) and to my dismay after I installed it the problem persisted.

Being that the car has 180k miles i'll give you a rundown of what I've replaced that seems pertinent

-Engine Wiring Harness (around a year ago)
-Alternator (around four years ago, tested 14.1 volts with engine running)
-Battery (going on eight years, but tested 12.6 the next morning after problem)
-Both Coil Packs (around a year ago)
-Spark plugs/wires (around a year ago, plugs gapped to .30)
-Fuel filter (three months ago)
-Air filter (six months ago)
-Cat (three months ago)

I checked the TPS for any internal damage or cracking, and verified it works by trying to run the motor without its harness plugged in

I cleaned the MAF, which from what I understand with this car the engine wont even run if it is malfunctioning

The car still uses original o2 sensors, although I did remove the harness from the first one (downstream?) while the engine ran rough trying to idle and no changes

Here's the kicker, I removed the harness from the IAC (new one) then started the motor and the engine would idle. Plug the harness in, and could repeat the stall out.

It will be about two weeks before I can drop enough money for a shop to figure this out for me, so I was hoping dropping some information here might lead me to the right fix before I have to spend money on something I could do myself. Only possibility I haven't factored out is if the new IAC Valve I purchased was defective, because I dissasembled the old one and during the process I broke it So, i'm hoping to find a used one somewhere to rule that out. Also, I have yet to have any codes checked on it yet, no CEL

Thanks for reading this and hope its something small I may have looked over


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post #2 of 3 (permalink) Old 09-29-2011, 12:44 PM
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MAF can cause your problem if it's just "out of spec" and not just totally bad. The car will run but will stall... Had a Mercury Mystique that the MAF was bad in it and it wouldn't idle and stalled all the time a used one from the bone yard cured the problem...
You might want to "pull" some codes from the ECM...I noticed that you did not mention any...Advance/Autozone will read them for you. CEL may not light with certain codes.
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post #3 of 3 (permalink) Old 09-29-2011, 01:44 PM
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Greetings Mike, and welcome.

If the IAC valve or ports were carbon coated, the next step is to clean out the carbon buildup from the throttle body and give the throttle plates a thorough cleaning.

This link may help:

What causes an engine to stall at idle but run fine over 1000 rpm

(I prefer to use regular throttle body cleaner, budget-brand.)

The only "trick" here is to limit, as much as possible, the amount of cleaner you introduce into the engine, as dumping vast amounts of cleaner into the intake manifold will ignite when you start the vehicle - Not good for the O2 sensors in the vehicle.

So, with the throttle plates at Wide Open Throttle (WOT), using a cloth rag (an old cotton T-shirt works best) inserted in the throttle body / past the plate(s), spray the cleaner so the rag soaks up all / the majority of the cleaner. *Do not use paper towels, etc: these can catch / tear on the throttle plate and fall into the intake manifold - then you'll have another issue to deal with..*

Use a soft bristled toothbrush to clean both sides of the throttle plate(s).

Shoot some cleaner directly on or dip in a cup of cleaner and scrub both sides of the plates gently until the carbon is removed, then wipe with the rag. Be as sparing as possible w/ the cleaner & Repeat as necesssary.

If heavily coated it will take several cleanings to loosen up the buildup: just take your time with it, eventually the carbon will loosen to where it can be wiped off.

If your throttle body has (2) plates, just do one side at a time.

After the throttle plates are nice and clean, and the IAC is cleaned up, try hooking back up, see if there is any improvement.

As to "why" the throttle body is building up carbon, most common causes are

Failing and/or biased upstream O2 sensor,
a dirty MAF sensor,
incorrect data from the engine coolant temp. sensor to the ECU.

All of these will make the motor run rich -> build up carbon.

If you haven't already, consider signing up at the kiatechinfo.com website (see my sig) using Internet Explorer: there you can see the fuel system troubleshooting diagnostic chart for your vehicle, which includes the indicated resistance values for the coolant temp. sensor for testing it.

While I don't generally recommend the use of "additives", adding a fuel system treatment 1 or 2x a year to clean the fuel system & injectors is not a bad thing to do.

I prefer to use a product called SeaFoam - I add about 1/3 can to a full tank of fuel every 6 months or so (just follow the recommendations on the label).

There are others who use it directly in the engine for cleaning, that's one of the recommended uses (you'll see this if you search the product on the internet.)

Given the amount of mileage on the engine, I would -not- recommend adding any "additive" product directly to engine oil: keeping up with a fresh oil / filter change using a quality oil regularly is really the best way to maintain & prolong motor life.

Some fans of SeaFoam use the product directly in the Intake Manifold by ingesting it through a vacuum hose at the intake manifold, turn off the motor, let sit, then start and run to loosen carbon buildup. This does work & has some merit, but again, depending on how much of the product used, I would recommend an oil / filter change immediately after doing this procedure, to remove any SeaFoam product introduced into engine oil while doing the "fogging" procedure.

(Apologies for the long "SeaFoam" digression, just want you to have accurate info. if you decide to use.)

Sea Foam | How to Use Sea Foam Motor Treatment

Good luck, and hope the info helps.

Laptop/USB OBD-II Scanner at Amazon: search "ScanTool 423001 ElmScan 5" at amazon.com
OBD-II Codes:
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