My 01 XJ with 178K ran great all winter. I put new Champions in it last June. Everything else works/runs great but I put the AC on the other day when we had a temp. Spike and it would idle pretty rough especially when in gear in reverse or even stopped at a light. What's causing this? I know the plugs are good, air filter is good and it runs great without AC.

 

check your voltage, get you battery tested....also when was the last time you coolant was changed? is it running at 210? any heat soak issues? those pre cats on the '00 and '01 XJ's make the engine compartment really hot and IMO puts a strain on the a/c system to keep it cool.

 

Battery is good....less than a year old...no issues there. Might be time to clean the IA C and TB again though. Never cleaned the IAC but cleaned the TB about 10 months ago. Steady at 210 and zero coolant loss.
I rule!

 

I would recheck the plugs too for fouling. Plugs have been known to foul if something isn't 100% Recheck the gap Make sure it's at .035. When was the last time you gave it a full tune up. Plugs, wires and everything else that goes with it?

 

It ain't got know wires.

 

Bluetooth ?

 

No

 

Sorry about that I missed that it is a 01.

 

no coolant loss-but when was the last time your coolant system was drained , flushed , and new coolant added?

 

Last April

 

are you getting a misfire? check engine light coming on? or is it just rough, like the vehicle is vibrating.

 

Good idea to clean the TB and the IAC pintle.

Remove the TB, remove the sensors, clean the TB completely, including the orifice where the IAC pintle seats. Be careful cleaning the IAC pintle, use a tooth brush and some MAF cleaner. You can use TB cleaner on the TB but be cautious using it on the pintle. Reinstall the TB using a NEW gasket.

 

Just rough and never a CEL.

 

Just had the same problem on my 99 xj, except all the time the idle would seem like a bad IAC or tps, replaces both of them & turns out I was low on AC refrigerant and it was working it’s *** off to cool the car, but all the time for me. So mechanic is refilling it and I’m picking it up soon to see how that worked.