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The engine very suddenly began stalling when you let off the gas pedal. It won't start unless you push the gas pedal down. Seems to have good power and runs normally as long as it's moving and the engine is under load but quits immediately when I let up on the gas pedal. The car has 85,000 miles. The Check Engine Light is not on and there are no codes stored. I replaced the air filter and spark plugs but the condition is unchanged. I have an IAC (Idle Control Valve) on order for it. Can anyone offer any advice on ways to narrow down the culprit? Thanks in advance.

mikey1

clean or replace the IAC....clean the throttle body/butterfly while your at it

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Update... I replaced the IAC (idle control valve), cleaned the throttle body and reinstalled with a new gasket. It already looked pretty good. Didn't fix the problem. It still runs rough and quits at idle. Still no check engine light or codes stored. It has new spark plugs and air filter. Any other suggestions on what to check / test?

mwhit0

Have you replaced any of the O2 sensors? I had almost the same issue on my '02 EX, there was no code for a bad O2 sensor, but I had a reputable mechanic check it out, determined bad O2 sensor, replaced it, and voila, no more stalling. It was the upstream sensor--I did have the downstream sensor fail on me around a year and some odd months later, and it did throw a code, but I never had any stalling issues with it, and replaced it myself for ~$26. The reason I mention that last bit is because I'm recommending you check out your upstream O2 sensor--or in your case, on the '04, probably a "fuel/air ratio sensor" (fancytalk for 'more expensive O2 sensor' as a former wrench I work with tells me).

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RESOLVED. Ended up being the EGR valve stuck open. Cleaned it and reinstalled it. Back to normal. Thanks for all your help!