Rough Idle when warmed up

[hunt4lif3]

I have a 94 explorer with 130k miles on it. Lately I have noticed that after I run it a good 20 minutes or so, turn it off, then restart it 5 or 10 minutes later i get a rough idle. It gets a little worse once i put it in gear, but after i give it gas it seems to clear up. I have replaced the fuel pump, fuel filter, fuel pressure regulator, all new plugs and wires, new air filter,cleaned MAF sensor and IAC valve. I dont know what else to try. Any help would be greatly appreciated.

 

[Anime]

What brand of plugs and wires? Using the OE Motorcraft plugs usually gives the best results in terms of performance and a smooth idle, sometimes aftermarket plugs, especially gimmicky ones, give worse performance and rough idle. Cheap plug wires often are worse than old worn out factory ones.

You might also want to check the bolts on the lower/upper air intake to be sure they are torqued to spec, leaky intake gaskets can give a rough idle as well.

 

[arco777]

I have the same issue, even with good quality plugs and wires. No codes are thrown either. Been living with the issue for years now, a minor nuisance since it doesn't happen often and the fix is throwing it in gear and driving 50 feet. Would be interwsted to know what the cause is. Heat soak of some component is one guess, perhaps an ignition component?

 

[hunt4lif3]

I'm using the Bosch IR fusion plugs and Bosch premium wires. Would the intake gaskets only leak when hot?

 

[wood1]

Rusty had a rough idle when hot and it was the elbow to the vacuum line on the fuel pressure regulator I think he said. Got soft when warm and leaked. It's in his latest thread, "Elvira".

 

[Anime]

^^^ Definitely check the regulator vacuum line.


Bosch plugs could be the cause of it. The only real way to find out is get 6 OE Motorcraft Platinum plugs and change them out.

Usually a leaky intake gasket would cause rough idle when cold, and seal back up once the engine warms up and metal expands, but there could be other things causing the gasket to leak, despite warm engine temps. Could also be a leaky vacuum cap as mentioned, and sometimes the plastic air intake tube can get holes or cracks in it.

Something else to keep in mind as the Explorer gets older is that the main computer, the PCM/ECU, in these, has bad capacitors that are known to leak corrosive electrolyte when they go, and this causes erratic operating issues as the caps continue to leak more and more until they eventually damage the circuit board beyond repair and the vehicle won't even start. You can always buy a refurb PCM/ECU for $100-200, but it's also possible to just buy new capacitors for a few bucks, and have them soldered in the replace the old ones.

 

[hunt4lif3]

It was doing the rough idle thing before i change the plugs, and i replaced that rubber connector from the regulator to vacuum line when i replaced the regulator last week. the old one was really loose and sloppy fitting, so i figure for a couple bucks why not replace it while I'm working in that area... anyone think it could have anything to do with a ECT sensor?

 

[hunt4lif3]

just noticed today that if you dont let it sit for more than 5 or 10 minutes before restart, the rough idle problem isnt there...this is driving me crazy, i know that it is only a minor issue, but i like for my vehicles to run right all the time.

 

[wood1]

EGR sticking or something maybe?

 

[hunt4lif3]

Would there be a way to test the egr before buying one to see if it helps?

 

[Mettler]

I was recently having the same problem. I had changed the electric solenoid on the IAC and cleaned it. But that didn't fix anything. I recently completely replaced the iac. Completely fixed my problem.

 

[hunt4lif3]

i should be getting a coupon from advance auto parts tomorrow, looks like i'll try to get a new IAC valve and see if it helps. I'll let you guys know something by wednesday.

 

[hunt4lif3]

got the new IAC valve installed, and i still have the rough idle. I cant understand why it only happens when the car is warm and i let it sit 10 minutes or so before i start it back up. If i turn it off and start it right back up there is no problem at all, but if it sits for 10 minutes or so it gets a rough idle when i start it back up. When i put it in gear (forward or reverse) the rough idle gets rougher until i start driving then it goes away. Someone please have the solution to this, it is driving me crazy!!

 

[wood1]

check for codes?

http://www.explorerforum.com/forums/showthread.php?t=255962

 

[hunt4lif3]

i read the posts in the link you shared. seems really interesting, i have never noticed the CEL being on when the rough idle is happening... I'll check for codes int the morning, but doubt I'll find anything... Thanks for sharing the link!

 

[wood1]

No problem, some times codes are stored and the MIL isn't on. Hopefully there is something stored that points to your problem.

 

[hunt4lif3]

just pulled the codes, i got a 116 and a 114 then the pause then a 111... checked the list from that link you sent and it said 116=Engine Coolant (ECT) sensor out of range and 114=IAT sensor out of range... is this because the vehicle was cold and had not been started, or are theses two sensors bad?

 

[MrShorty]

Yes, running the test on a cold engine is a common cause of those codes. If you let the engine warm up and then repeat the test, do they go away?

Another test I would do: put a fuel pressure gauge on it and see if the fuel system is up to snuff when it is idling poorly.

 

[hunt4lif3]

just checked the codes after it warmed up and got two 111's...fuel pressure is reading around 37 psi when its warmed up

 

[gmanpaint]

It is a bad Temp sensor.

http://www.rockauto.com/catalog/moreinfo.php?pk=951148&cc=1119631

Been here, done that already on the 94.

There are (2) sensors, so make sure you change the one that has a cone on the end of it, next to the thermostat housing.