94 Rough Idle after warm start

[GA1990]

After I drive my explorer for a while, then let it sit for maybe 15-20 minutes, if i start it up again it has a lumpy idle. Any ideas? It happens even more frequently if i've been pulling a trailer or doing something to make it run exceptionally warm. I've got about 115,000 miles on it. I also can't get rid of the nock these days, except with premium gas...I've clean the maf multiple times, that use to make it go away, but not anymore. I was wondering if the O2 sensors could be the culprit..I'm very good about routine maintenance, but they're one thing that's still original.

 

[bates]

someone will probably say IAC so ill be the first.

 

[MattPersman]

I am going to take a shot and say fuel pressure regulator. Sounds just like mine was

 

[dogfriend]

Originally posted by bates
someone will probably say IAC so ill be the first.

Ill be the second. Does it idle slower than normal? Say 500 rpm instead of 800rpm? If so, I would say IAC.

This is the first thread that I posted to on this board:

Dead Link Removed

 

[GA1990]

Well I cleaned my IAC and that didn't help, so I replaced it, and still, same problem. On really cold starts (if it's cold outside) it stumbles like it's going to die, and on warm starts it idles really rough, and sometimes the idle will drop to about 500 rpms, it never dies though. After I drive a little bit it's fine. I've checked for vacuum leaks, all the lines look good, and I sprayed some intake cleaner around all the lines and intake to see if I could get any reaction, but nothing. Any other ideas?

 

[GA1990]

Also, is there anyway to test the fuel pressure regulator? Has anyone else had a fuel pressure regulator cause probs like this?

 

[dogfriend]

Are you getting a check engine light??

 

[GA1990]

No check engine light.

 

[dogfriend]

You would test the fuel pressure regulator by testing the fuel pressure at the fuel rail port.

 

[MrShorty]

Try pulling codes from the computer, even though the CEL isn't lit. Sometimes the computer stores codes or there are hard faults present that don't illimunate the CEL, but that show up during the self-test.
Definitely test the fuel pressure.
Somewhere someone said that the fact that temperature seems involved may point to an electrical problem. What's the status of the spark plugs & wires? Do you have a timing light or some other way of checking to see if each cylinder is firing?

 

[Rhett]

Besides O2s or FPR, another possibility is the fuel pump relay going bad.

Sometimes the relay will not flip over right away, and effectively shut down your fuel pump. Then it will suddenly flip back after a few minutes or seconds and the truck will run fine. This happened to mine a while back. The relay is under the hood on the pass. side in the relay box. It's identical to the ABS relay (same part#) so you can switch them around and see if your ABS light comes on.

 

[GA1990]

Thanks for the idea, I'll try that as soon as i get home. I've had problem after problem with those relays, but I think the last time I had a problem (blower relay), I replaced all of the ones i hadn't replaced before. You think they could design a more reliable relay.