Engine Idling Issue


New Member
Jun 15, 2014
Hey everyone, need a more car savy feller to assist me today. Here's my issue:

My 03 GT was beginning to stall whenever I slowed down at a light, sign, etc but it idled fine. My first thought was the IAC was going bad. So, after finding one at autozone, I replaced the part and solved the stalling issue of slowing down. However, my car now will stall after idling for a few seconds while sitting still, in drive or neutral. So the next culprit on my list was the TPS, I changed it out and the issue was still prevalent. Next bad guy was the EGR valve, I just replaced it with a new one and the problem is still there.

One note on this, after changing the IAC my car also started idling high, around 1500 rpms, then abruptly drop and die. I also noticed that when cruising at a low speed (5-20mph) my car would slowly speed up on its own and eventually would shift into second. I have also thoroughly cleaned both the intake Plenum and throttle body.

Any ideas gentleman?

Edit: I have also checked all vacuum lines and there appears to be no un-metered air getting in.
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15 Year Member
Dec 3, 2002
Seattle area, WA
Try cleaning your factory IAC and putting it back on. Use break cleaner, not carb cleaner.

Don't just throw parts at a car and hope they will fix your issue, that's how you spend a lot of money for nothing. You need to diagnose the issue and replace parts intelligently.


SN Certified Technician
Aug 14, 2009
Houston Texas
At the risk of sounding like a broken record.......

Have your battery and alternator checked. Make sure the battery holds a charge. All battery cables are clean and tight.

Don't fall victim to the belief that the motor quitting suddenly couldn't be something as simple as a bad battery or loose battery cable. Don't be "that guy" who replaced a bunch of parts only to find it was a common maintenance item.

Save your $$ by not replacing the TPS. It's unlikely to fix your problem. At the very least there are a ton of more likely items to check first.

Hint. Just in case you are wondering. The most common symptom associated with a bad TPS is a high idle.

Here's some more information about how to trouble shoot IAC/idles issues.


Active Member
Sep 30, 2016
Please, please, do a dtc codes test. I can't tell you how many forum members start throwing parts on endlessly, just to have same problem. Think about this for a second, when you go to your doctor with an ailment, he or she asks lots of questions, runs tests, X-rays, maybe MRI. They never guess. That being said, I would not rule out that you still have a vacuum leak, albeit a small one. I also agree with other member, return your iac you bought. Take your old one apart, spray and clean out completely. They get clogged up with carbon. Usually cleaning out an oem one works better than most replacement. Please replace gasket on iac when you do. Remember idling problems get worse as vehicle warms due to fuel trim leaning out. I've always checked intake leaks with wd 40 spray and the red nozzle. Spray around intake gaskets everywhere. You can also use a carb cleaner spray. It's more sensitive to leaks, so you have to be more alert. Keep us posted what you find as always.

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