PLEASE HELP! Runs rough cold!

Hi,

94 5.7 TBI.

Runs really, really well, except during cold start. Will start OK, idle will go right to 1100 (or so) RPM, but start to run rough after about 10 seconds. It get progressively worse, to a point that if you rev it, when it comes down it almost stalls before catching itself. Doesn't hesititate, and once in gear and your moving it seems fine. After a maybe 5 minutes, it's just fine.

I've replaced all tune-up parts, PCV, no codes.

Could it be Coolent temp sensor, or IAC, or EGR?

It's driving me nuts. Any help would be appreciated.

Thanks

Scott

Hi,

Could it be Coolent temp sensor, or IAC, or EGR?


Yes it could be any one of these I would start with IAC first though.

You can disconnect the coolant temp sensor to see if that is the problem. When it is disconnected, the PCM thinks the engine is cold.

If the problem goes away when it is disconnected, then you found your problem.

//2000CAYukon

You can disconnect the coolant temp sensor to see if that is the problem. When it is disconnected, the PCM thinks the engine is cold.

If the problem goes away when it is disconnected, then you found your problem.

//2000CAYukon

Thanks. Since it was only $8, I picked up a coolent temp sensor last night, put it in today - made no difference.

I disconnected the IAC plug, and while there was no change to the RPM, I thought perhaps it may have run a little better.

I moved the EGR from behind and it felt fine.

It's weird, it runs perfectly once it's been running for about 5 minutes...

I think I'll have to take it to the dealer, I don't want to keep throwing parts at it...

Thanks again

I have the same problem but now it has gotten worse over a years time and I get a code 44 please let me know how you make out maybe i have the same problem

So I've replaced the EGR, and the TBI base gasket. EGR solenoid is OK. Driver's side injector drips fuel at idle, but does not leak when you charge the pump without starting the truck.

I start it in the morning - it turns over more than you would expect, but not so long as to seem strange... and when it starts it goes right to 1200 RPM and runs glass smooth.

After about 30 seconds though, it begins to run rough. It farts and stumbles a little, and the RPM's go down - just like a carb that won't choke right. If I apply throttle, it will bog and then seem to clean up and run smooth. Back to idle it's good for about 5 seconds and then back to running rough.

You can smell it's running very rich - and even when it's warm and running well it seems to smell a bit rich. The tailpipe is black with powdery black soot.

Once it's in gear and you drive it's OK - no hesitation. Untill it's warmed, however - maybe 6 minutes, it continues to idle very, very poorly.

Once it's warm, it runs very well indeed.

I'm really pulling my hair out here - regulator, that injector? Any ideas???

Thanks

Injectors should never drip-probably your problem.