'95 ATX rough idle after shut off hot

[kumba]

I am having an issue where after driving my car around and it getting to normal operating temp it becomes rough starting and idling. Once I do get it started I usually have to rev it up to 1500-rpm or so for 10-15 seconds after which it usually starts to idle correctly. The problem does not happen if the car never reaches operating temp. The problem reminds me of a carb set-up where the fuel would percolate in the bowls under a hot engine bay.

Is there a most likely culprit I should be looking for?

 

[deercrusher]

The best place to start is check for codes. Otherwise you are taking a buch of guesses trying to figure it out

 

[hawkeye18]

I am having an issue where after driving my car around and it getting to normal operating temp it becomes rough starting and idling. Once I do get it started I usually have to rev it up to 1500-rpm or so for 10-15 seconds after which it usually starts to idle correctly. The problem does not happen if the car never reaches operating temp. The problem reminds me of a carb set-up where the fuel would percolate in the bowls under a hot engine bay.

Is there a most likely culprit I should be looking for?

This is actually a fairly normal condition in SHOs. Nobody's really figured out the exact cause of this (or if they have, they aren't sharing), but my best guess is that it has something to do with the metal intake getting hot with the rest of the engine. When you start it up, the air at the IAT is significantly cooler than the actual air in the intake as it's been heat soaking for a while. This makes the car dump waaaaaaay moree fuel than it needs into the air and makes it stumble until you get enough air through the intake that it cools down.

This has happened on all three of my SHOs, usually after not turning the car on for 10-15 minutes after letting it warm up all the way. Solution is just taking the engine RPM up to what should be about 2500 and just keep it there until the engine magically jumps up 700-900rpm.

 

[trainguy1989]

Mine does that too.

 

[hawkeye18]

Mine does that too.

See? Everybody's does that. Nothing to be alarmed about. Just consider it another one of the quirks of SHOdom.

 

[luigisho]

It could be the check valve on the fuel pump return has degraded and some of the fuel pressure has leaked back into the tank. THere used to be a picture in old threads. Might have been lost in one of the bad server crashes a while ago.

Look at pictures 6&7 on this page. You will see the check valve (little red rubber thing on the end of the return tube).
http://www.shotimes.com/php-bin/mod...le=article&mode=thread&order=0&thold=0&sid=75

 

[joesho_gb]

Dumb answer, but mine did this. Disconnect the front and rear bank O2 sensors and see if that helps. (Wire harness on both).
You'll get a CEL once the engine warms, but if seems to run right, it's one or both of those. Mine did that, and I kept getting a LEAN CEL for both banks, and under 16k RPM, ran like crap.
Pulled the O2 sensors, and away it went.

I did some research, and until the motor reaches normal temp, the computer will check the O2 sensors, but won't change the way the motor runs. But, after it's warm, it thinks the engine is running lean, it will try to make up for it. Same with rich.

Good Luck!

 

[rubydist]

kumba, it is a very common problem, most of the SHOs that I have had have done that.

I think it has to do with fuel leaking out of injectors that don't quite shut off. This causes a very rich condition at hot restart, which can be cleared up by running the engine at a fast idle for a while, as you describe. The solution would be to clean and/or replace the injectors.

 

[kumba]

No new codes

I get a code about the ABS (which is disabled because of rotten/busted tone rings), but nothing else since I replaced the thermostat and fixed the cats.

The symptom is exactly like was mentioned. The trick is to feather the accelerator when it kicks over to get it to rev up, hold it at around 1500 where it runs rough, then about 15-20 seconds later it revs up and runs smooth after that. Symptoms are pretty much exactly like Hawkeye said. If I let it sit for 30 minutes or so, I can come out and fire it up just fine.

It was just a little unnerving when it first happened.

 

[hawkeye18]

Dumb answer, but mine did this. Disconnect the front and rear bank O2 sensors and see if that helps. (Wire harness on both).
You'll get a CEL once the engine warms, but if seems to run right, it's one or both of those. Mine did that, and I kept getting a LEAN CEL for both banks, and under 16k RPM, ran like crap.
Pulled the O2 sensors, and away it went.

I did some research, and until the motor reaches normal temp, the computer will check the O2 sensors, but won't change the way the motor runs. But, after it's warm, it thinks the engine is running lean, it will try to make up for it. Same with rich.

Good Luck!

16 thousand RPM, huh? Did it run fine over 16k RPM? :laugh_ti:

I get a code about the ABS (which is disabled because of rotten/busted tone rings), but nothing else since I replaced the thermostat and fixed the cats.

The symptom is exactly like was mentioned. The trick is to feather the accelerator when it kicks over to get it to rev up, hold it at around 1500 where it runs rough, then about 15-20 seconds later it revs up and runs smooth after that. Symptoms are pretty much exactly like Hawkeye said. If I let it sit for 30 minutes or so, I can come out and fire it up just fine.

It was just a little unnerving when it first happened.

I remember the first time it happened to my wife in her car. we were both in our cars leaving the hospital and as I'm getting about a minute out she calls me in tears saying her car's broken!!!!1!1*sob*. So I'm like "wtf" and pull over to try to help figure out what's going on (getting back there would have been difficult, didn't wanna have to try unless I had to), and basically it was that. lol that was funny... and a long time ago. Now, if the same thing happened she'd be like "wtf stupid car!"

 

[joesho_gb]

16 thousand RPM, huh? Did it run fine over 16k RPM? :laugh_ti:

Oh yea, ran like a top! HAHA. Ok, so it's late and I screwed up typing,