In the last couple weeks my 00 2.5L auto has had a slight to bad stumble at idle and more recently a stumble cruising at 50-60mph under light to moderate load. When it's happening the only common factor is the engine is running and it's at operating temp. Doesn't matter if the AC compressor is on or off and it also does it with the hvac switch turned to any position. I did a major tune up about 2 months ago which included wires, plugs, cleaned MAF, both O2 sensors, pcv, fuel filter, iac and I cleaned the entire intake and tb. I did all of that in one day and have put over 3000 miles on it since then without a problem. All the replacement parts were Motorcraft.

When it's stumbling the CEL doesn't even flicker and the transmission feels fine. I have checked all of the vacuum hoses for leaks as well. A couple of the hoses are cracked but don't seem to have any leaks.

It's never consistent (other than it only happens when the engine is warm) and mostly happens at idle. It can be just a hickup or start rockin like it's got a monster cam in it. Then engine never dies.

I unplugged the iac while it idling very rough and it seemed to even out pretty well, I also gave it some gas and the revs went back to idle fairly well but it never dies.

I have cleaned the MAF and IAT sensor with no change in the condition.

I put a fuel pressure gauge on it and it held rock steady at 68psi while idling fine and while it was idling rough.

Suggestions? I have never touched the EGR system or the coil packs. This truck has 134,000 miles on it as well, could this problem be a sign that the timing belt is about to break?

 

CHANGE THE COIL PACKS BRO...if you changed the plugs and wires, you gotta change those coil packs...

 

My 97 was doing the same and I thought that the coilpacks couldn't be the problem...$350 later, a local shop replaced my coil packs a my truck ran fine...I could have saved so much money if I would have just changed them myself...BTW....i had also replaced the plugs and wires without replacing the coil packs....

 

Thanks for the replies.

ok..............now it's not really having a problems at idle but it's having massive problems while driving. It has almost no power and is stumbling hard while driving in all load conditions and speeds. I ordered new coil packs the other day and they should be on my doorstep in a couple hours.

 

Changed the coil packs and it seems to be purr'n like a kitten now.

 

ok, the coil packs didn't fix it. I just changed the IAC again and no luck either. I unplugged the new iac while it was running as well and it didn't die. I unplugged most of the vacuum lines I could get to and plugged them, no change. I unplugged the hose from the EGR several times today and no change as well. All of the times I unplugged the vac line from the egr it wasn't pulling air anyway. I think I'm just going to take it to the shop at this point.

 

Sorrry to hear the coils didn't fix it...at least they are new now...check all your vacuum lines...I have had clogged lines in the past...make sure they are not plugged...

 

Change your plugs again. I put in new plugs back in may and I had one of them go out in early july.