Rough Idle when engine is hot HELP!!! 1993 explorer

[Shane Fazzino]

Hey guys,
I have a 1993 Explorer XLT with 120,000 miles bone stock. Since I purchased it in March I have noticed that when the engine gets very warm like around or above the M in normal, (from idling with the AC on to cruising the highway in 100 degree weather) when I shut the car off and around 5-20 minutes later try to start the car, it fires right up but shakes a lot and runs rough, until I blip the throttle then it goes back to normal. Normally the car shakes a minor amount but i was told most V6s do. But when it starts really hot like that I know the shaking is not normal. Any help trying to diagnose this issue?

 

[timtimtimajim]

I used to have the same issue with my Explorer. It went away when I put a new engine temperature sensor in. It seems that the old sensor was worn out, so when it would get warm the engine would run rich and idle rough like that. That would be where I would start

 

[Shane Fazzino]

but did yours idle poorly all the time or would it go away once you revved the engine a bit?

 

[timtimtimajim]

It would go away once I revved the engine a bit

 

[Shane Fazzino]

I will get to that then and post an update later on

 

[Shane Fazzino]

i tested the temp sensor by taking it out of the car and using a heat gun. I heated it up to running temp and it showed the correct resistance that I found in a repair manual. What else could it be?

 

[Dora 1993]

When was your last tune up? Could just simply need some plugs! The girlfriends Blazer needs a tune up. Idles a little rough and shaky and throws misfire codes but when on the gas it's smooth as butter. For now.. lol

Also how many RPMs do you idle at?

 

[gmbroy]

ok your problem is one that is common with the first gen. I had the exact same problem . i replaced the lower intake manifold gasket , & run non ethanol gas . no more problem . while your in that far you can clean the injectors & replace the o rings if you want . i run fuel system cleaner & it does help . I have 315,000 miles on my explorer .

 

[TDG]

i tested the temp sensor by taking it out of the car and using a heat gun. I heated it up to running temp and it showed the correct resistance that I found in a repair manual. What else could it be?

Which temp sensor did you test? There are two of them from what I've read, one for the EEC and for the gauge.

 

[gmbroy]

as tdg has said there is 2 . the one on the left of the gooseneck goes to the guage . the one on the right has 2 wires & sends the temp to the pcm . it is called the ECT engine coolant temp . you can try that first but in my case it did not help .Just keep us informed we will help you all we can

 

[TDG]

Since you have a meter and the skills to use it you could try popping the ECM out from under the passenger side kick panel and measuring senor input values (ECT / IAT / MAF / 02 etc) under normal conditions and again under rough running conditions, that will tell you pretty quick if your condition is being caused by a lazy / overheated sensor / electrical or something more mechanical in nature.

Moving up the scale of risky things (assuming sensor / electrical issues have been ruled out) I would be curious as to what fuel manifold pressure is doing during the rough running events; my 93 with a cheapo fuel pump would chuga chuga a bit when it started hot and it measuring the fuel manifold pressure showed that was losing pressure when shut off at a rate higher than allowed, might also have been getting some air in the system. I suspect the check valve in fuel pump was contaminated with crap from the old gas in the tank since I could not find any other sources of pressure loss, changing to a new higher quality pump eliminated the issue. (and the loud fuel pump whining sound)