schmidtty

I bought a 2004 gt mustang almost a year ago now, with over 120k miles on it. I suspected there would be problems when I bought the car. But after a few months the car started to stall at stop signs and lights. I would hear this popping noise when the car sits and rpms would move from 1200 to 400 and then stall sometimes. I believe its miss firing but I have changed the spark plugs, had the fuel pump serviced, and changed the idle air control valve and still have the same issue.
any thoughts? and what can i do to fix this? thanks in advance.

cliffyk

"Miss firing" sounds like a beauty contest...

Is there any sign of misfiring when you accelerate briskly from lower rpms, starting say at 1500 in 3rd gear?

How long ago did you replace the IAC, when you replaced it did you disconnect the battery for 5-7 minutes to reset the KAM and force the PCM to relearn the idle air trims?

When you changed the plugs did you examine the COP boots for hardening, cracking or other signs of deterioration or high Voltage breakdown? What plugs were used as the replacements, were they gapped correctly (0.054")?

At higher speeds how does it accelerate? For instance if you are going 50 in 3rd gear and "nail it" does it pull well right up to 5000 rpm (85 mph)?

What does "fuel pump serviced" mean? Was it replaced, strainer cleaned, filter changed, please explain further?

EddyG

hey i have the same problem and mine misfires at low rpms. what could it be i changed the iac valve. looked forever for vacuum leaks. im so stumped. and it also accelerates fine in high rpms and high speeds.
What are some things that i should look for that causes this.

schmidtty

Sorry about the late reply been busy for the holidays.
For your questions i have noticed some misfiring when accelerating from low rpms.
I replace the IAC about 6 months ago now and I had a shop replace the fuel pump. They also did change the filter. When I did change my IAC I did disconnect the battery for about 10min. I replaced the spark plugs with bosch and they were gapped correctly. I check the previous spark plugs, I don’t remember what they were, but they were still good with no high voltage break down. And I replaced the boots the same time I changed the spark plugs.

cliffyk

My thoughts would turn to the EGR valve then, it's likely sticking and closing too slowly.

My '03 GT developed that same sort of misfire, low rpms and light load acceleration, and I suspected the EGR--sure enough disabling it in the tune made the problem go away. I have never bothered to replace it as we have no emissions testing here in Florida.

They are $65 or so at any FLAPS...

schmidtty

hmm ill take a look at that. thanks for your help