Continunig rough idle

[blue_lightning]

:exp:

I was in Utah in June and the engine started overheating on my 1994 Explorer so I replaced the thermostat with a 180 degree t-stat. That fixed the over heating problem. After replacing the t-stat, I drove around Denver for a week then back to St. Louis. About 2 weeks later I started having a rough idle.

I had Autozone and Advance Auto check the codes but neither place was too sure how to use the reader so I don't feel comfortable with any info. they gave me.

After viewing several posts, I replaced, one at a time, the PCV, MAS, IAC and DPFE but still had a rough idle so I took it to a ford dealer. They have no idea what the problem is.

I don't get a check engine light but I'd like to know which terminals to short so I can use a flashing CEL to possibly diagnose this and any future problems.

A few posts stated that replacing the O2 sensors solved their rough idle problem.

Is it possible to have a bad O2 sensor and not get a CEL? and could a bad O2 sensor cause a rough idle?

Thanks

 

[mikeinri]

Welcome to the site!!!

First thing I'd be looking for is a vacuum leak. They cause idle issues, and are very cheap to fix (once you find it).

Unless you've replaced these items recently, from what you're describing, you may just be due for a tune up consisting of the following basic items. These would be the most likely, routine-maintenance items to affect idle.

Spark plugs
Ignition wires
Fuel filter
Air filter

If you search this site, you should be able to find a paper clip method for reading the codes, or you can buy a basic code reader at a good parts store.

You could have a blown bulb, does the CEL come on when you start the truck?

Mike

 

[blue_lightning]

I replaced the plugs, fuel filter and air filter in May this year. The wires have about 30,000 miles on them.

None of the vacuum lines look cracked or dry and I've sprayed starting fluid all over them and the engine doesn't react.

The CEL does come on when I turn the key to start.

I'll check the plugs and shake the wires tonight and see what happens.

Thanks Mike,
Larry

 

[aldive]

Take a look at http://www.explorerforum.com/forums/showthread.php?t=169335&highlight=quest

 

[mikeinri]

OK, your CEL bulb is working, that means you aren't currently getting a code. If you check codes, you would most likely only see CM (memory) codes, if there are any stored.

So, without a code, it makes it a little tougher. Assuming the computer is working, all your sensors are probably OK (although cleaning never hurts). I have seen a lot of posts here referring to fuel pressure issues, although I'm not sure if that would only affect you at idle. Could also be a clogged injector, I suppose.

I hate guessing, and you've probably already thought about anything else I'm likely to post here, so hopefully someone with more experience with this problem will chime in. I've been lucky, my only idle problems (so far) have been addressed by fixing vacuum leaks...

Mike

 

[93TwotoneXLT]

Check your intake gaskets for leaking. These trucks will leak at the #5 cylinder and cause a rough idle condition. The way to check is to pull the spark plug and check for a white build up on the plug. If you see this, then either the lower intake gasket is leaking or the head is cracked. I had the same symptom on my X. After replacing the lower intake and valve cover gaskets I have not had a problem yet in 20K+ miles. While you are in there you may as well replace the injector "O" rings and the FPR. It is cheap insurance against possible future problems. Good Luck.

 

[Explodr94]

Make sure all your fan blades are there. That was the problem on EX.

 

[blue_lightning]

I replaced the fan, fan clutch, temp. sending unit and belt tensioner in July this year. The fan had several major cracks around the hub. I think it was running on borrowed time.

Last night I re-checked all the plugs. They all looked good and the gap was good. I also replaced the wires. The ones I had were older than I thought. Didn't notice any white buildup on any of them, around the valve cover or head.

Still idles rough. When I start it in the morning, it coughs and chokes and sounds like a slight backfire. I'm thinking of replacing the coil pack today.

 

[mikeinri]

Backfire = running rich... at least on my lawn tractor... But, you say the plugs weren't fouled???

Weird that the Ford dealer had no clue.

Mike

 

[blue_lightning]

I replaced the coil pack Wed. after work. It was running so badly I didn't know if I would make it home. Thur. morning it was a lot better but still a little rough. Thur. after work it was better so Fri. morning I replaced the plugs. I'm not sure how far you have to drive or how long it takes for the computer to readjust. On a 14 mile test run I didn't have any problems and so far the idle seems perfect. I was running out of parts to replace.

 

[Explodr94]

It sounds like you have replaced all the easy stuff. Now you have to go by the book, because it is either vacuum, fuel, or spark. Check your vacuum diagram and all vacuum lines, if they are wet or lubed, pressure test your vacuum modulator. A common problem with vacuum leaks was the intake gaskets. Fuel - check fuel pressure. Use a stethescope to listen to your fuel injectors. When they get clogged car runs like ****. Spark, usually when you run for codes, it will expose spark. However, I think it's either vacuum or fuel. Just my two cents.

 

[mawrazen]

Vacuum leak or bad tranny modulator!

 

[boatmoter]

:exporange 5 miles for the pcm to do a relearn, it sounds to me after all the bases you covered, and nothing showing up on fords scanner,you may have boiled the oil in the lifters when you overheated it,causing a little goo to form inside your lifters,they may stay pumped up a little longer than supposed to,you may want to try running a quart of engine flush thru it and then change the oil and filter useing a quality oil.. and drive it around for a while,I have seen it happen before on different vehicles,worth a try.. also some transmission rebuilders recommend servicing the transmission after overheating the motor,trans fluid gets burned..