Rough idle - Really Stumped

[Jim Jermain]

I have a '00 Explorer with the 4.0 OHV. Occasionally I get a rough idle for 30 - 60 seconds after the trucks has been sitting for a while (typically for at least 4 hours). I've tried cleaning the IAC, and MAP. I replaced the upper and lower intake manifold gaskets. I also tried replacing the plug wires and since I occasionally also get a P0303 (lean no. 3 cylinder) trouble code I tried replacing the no. 3 injector and plug. The truck as 74K miles. Any other tips on what might be causing the issue? I think I am running out of things to replace. Typically when I've tried some of these fixes the issue goes away for a few days and then it comes back.

I am really stumped. I certainly appreciate any tips.

Thanks,

Jim

 

[gtyates]

Sounds like my truck as well. Do you also get an rpm drop when you lift your foot off of the acccelerator, such as just after topping a small hill and lifting foot off accelerator to stay at the speed limit? Mine does this in addition to what you describe.

 

[2000StreetRod]

Replace fuel filter

I suggest that you try replacing the fuel filter if it's been more than 30,000 miles since the last replacement.

 

[alohamonte]

I chased a rough idle for a long time.

Check the PCV and PCV elbow/hose as a blockage or leak can cause problems. Make sure it's seated flush.

Cleaning the MAF and IAC might not be enough to repair it. I believe I replaced the IAC around 75k. The MAF at around 125k. You can also clean the Throttle Position Sensor (TPS).

When you replaced the upper intake gaskets, did you clean out the throttle body and fuel injectors? Replace O-rings? Both are highly recommended. The lower rev'ing OHV is known for carbon buildup.

Replacing the EVAP Pressure Sensor and EVAP Control Solenoid helped my idle.

Have you reset the computer (disconnected the battery) between fixes?

 

[Jim Jermain]

Thanks for the great tips. I forgot to mention I did replace the fuel filter, PCV valve and the injector o-rings as well. I also tried cleaning the throttle position sensor. I haven't tried playing with the EVAP system. I will check that out as well. I did notice one of the Differential Pressure Feedback hoses on the EGR was really in bad shape. I'm not sure if that would impact my idle, but I tried cutting the hose back and it seems to be running a little better. I'll keep you updated.

Thanks again for the advice.

Jim

 

[Tbirdsims]

Idle Air Control Valve, My SOHC was acting the same way, almost stalling when sitting at a light and all, i cleaned it a few times and it worked but then that wasnt working anymore, just got a new one off of RockAuto.com, half the price that every other place wanted for it and since i replaced it it runs like a champ!

 

[Jim Jermain]

Guys thanks again for all the great tips. I thought I update you on my diagnosis. I checked the compression on the cylinders thinking I might have a head gasket leak. I come up with 135 exactly across the cylinders. I also checked the EGR system and that seems to be working fine. If I disconnect the IAC, the idle immediately drops and almost stalls. This leads me to believe my problem is probably not the IAC unless it is getting stuck at start up.

What's really weird is the fact that the idle is only rough for about 30 secs. After that time it smooths out and runs perfect, no problems at all. This seems to point to the famed intake gasket issue. However I don't think I can replace anything else on intake. I replaced the EGR o-ring, upper intake o-rings, fuel rail gasket, injector o-rings, and lower gasket. None of which solved the problem. I am getting good vacuum to the EVAP system. However I probably need to do a little more testing.

I'll take any other thoughts. I am really stumped.

Thanks,

Jim