98 Sunfire GT shutting down after 1 or 2 hours

[redlemon]

After running well into full warmup, this car will stop running when I take my foot off the gas to slow down. Sometimes it will idle fine at a stop sign and sometimes it will die. No stumbling or missing, just dies. When it does start acting up like this it is almost impossible to get it moving without dying.

Fuel pressure is at 45psi. The following sensors and equipment have been checked for resistance, function and backprobed where called for by the repair manual, and all check out fine: TPS, IAT, Idle Air Control, no vacuum leaks that I can find, smoke test shows no vacuum leaks, Spark plugs replaced. It has thrown codes p0171, p0172 and p0441. I also ran a computer OBDCOM program in my laptop over a 200 mile drive and everything appeared normal such as fuel trim, O/2 sensors, timing, vacuum, IAT, operating temp.

It was towed to GM and to a large independent repair shop in the last month, no help. All testing whether it be mechanical or electrical has been unhelpful.

I did the reset for the PCM, no help. It is not a vacuum leak at the brake booster.

It always starts right back up when it dies. idles perfectly, but usually can't give it any gas or it dies. Does NOT load up on fuel.

by the way this is a 2.4 engine.

the thing runs like a brand new car until this starts happening, always after it has been driven and warmed up.

 

[melsg5]

When the engine dies nobody can find any codes in memory?

 

[redlemon]

No codes either time at the repair shops.

The codes I listed appear to me to be a result of the poor running rather than a cause. Last time out it was cutting out so much I wasn't sure that I would get home. about 10 miles from home it threw the P0171 lean bank cone code, that's the second time that code showed up. Can't find any vacuum leaks.

 

[melsg5]

Just a wild guess, how about the coils failing when hot? After it dies how long before it will start again?

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[redlemon]

Fires up immediately and runs fine. Usually dies again when the throttle is touched.

If it was carbureted I would say it acts like a bad accelerator pump.

 

[redlemon]

Do you think that, even though the Idle Air Control test right electronically, the plunger may not be moving back into its seat?

If so then it would idle properly but would die from too much air when the throttle is used AND could caused the P0171 lean bank one code.

Whatdyathink?

I hate to just resort to buying parts.

 

[melsg5]

found this write up on the IAC, is the port clean where the valve is located? Is the O ring in good condition?

http://www.automotiveforums.com/t663849-idle_air_control_iac_testing_replacing_cleaning_for_99_.html

 

[redlemon]

Thanks for the information

I cleaned the port out a month ago, i've seen worse but it did need some attention. So. the port is clean, the plunger is stained black but clean. The o-ring appears fine, looked at it again yesterday when I retested the unit.

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[redlemon]

do you happen to know what the normal -engine off- position of the pintle is on the Idle Air Control? Open or closed? I just happened to think of the smoke test I did yesterday. The only smoke I found was coming through the throttle body out of the IAC port. If it is normally open when the engine is off then fine, but if not then it would mean that the pintle is sticking open.

 

[redlemon]

Thanks for the hints Melsg5.

I think I'm just going to replace the idle air control valve for now. i also have not looked at the egr valve so I will remove that and see if it needs cleaning.

Will add to this thread when I have any news.