So, I know about the cylander 3 misfire issues and have read up on fixing that with a heat shield and or a fan to blow out the extra exhaust. But, today I had the misfire issue and when I turned the AC on, it iddled really rough and was vibrating really bad. Anyone have any idea where to start?

 

Year/engine? Have you changed plugs yet?

 

It's the 2000 XJ 4.0 i6 with 130k on it. Haven't changed the plugs but checked them last tune up, and they seemed fine. Doesn't run rough unless AC is on.

It was hot today and I had someone else driving it. We were in the parking lot and he kept turning it on and off like 3 times before i said something. I thought that he probably just got the fumes in the engine compartment that led to the misfire, but the AC thing is wierd. It runs really rough at idle with the AC on now.

 

Best to change plugs to rule them out. Can't tell all that much by looking at them; can have a cracked insulator, etc. It's a cheap investment and it needs to be ruled out. It's money well spent no matter how you look at it. I recommend NGK and be sure the gap is .035.

If it's warm, you might be suffering from "heat soak". Very common on the 00-01 as you have already read. Don't read too much into the AC wildcard. It might just exaggerate the heat soak.

The recommended Jeep TSB for heat soak (wrapping the fuel injectors) can help a bit, but mostly for MILD heat soak. Anything more than that and that TSB doesn't help much at all.

 

Thanks for the quick reply. I'll do the plugs at my next oil change which is in two weeks. I'll run without the AC in the mean time and update here when I know more. Thanks!

 

Compression test. Rent the gauge from autozone for free just to rule out the head before you start throwing money at it

 

Is there a noise under the hood? How's the AC compressor?

 

Compressor is only a year old. No noise, engine sounds perfect like a sewing machine. It's only why the AC comes on that it starts to shake and bog a little.

 

Check your belt alignment,esp. at the ac pulley. And the belt tension.
Also check all ac & ac bracket bolts for tightness.