Now with cold weather here, I don't have the AC on and I've noticed my 2000 XJ having a low, rumbling idle. Didn't notice this before bc the compressor always kept the idle in the 700 range.

RPM at a stop light in drive wavers between 450-550 and there's a definite low pitched rumbling sound. It does not happen in park however. In park the idle sounds normal and sits about 650.

I've tried cleaning the throttle bottle and IAC. Already have new plugs and air filter. Sea foam my gas every 3k. I replaced the throttle position sensor to no help.

I'm thinking my next step is to replace the IAC but that's a pretty expensive ($70) part.

Anyone with any ideas or experience w low rumbling idle?

 

For what it's worth, when I had idle issues I cleaned my IAC (twice, in fact) and ended up replacing it with a NAPA part, that fixed it.

I would check the voltage readings/smoothness of sweep of your replacement TPS, you could have got a bad one.

For my '97 (not sure if the numbers are the same for your 2000)

Throttle Position Sensor
Center lead-back probed/Key On-Engine/Off
IDLE: Greater than .350v. Less than .900v
WOT: Less than 4.5v


Analog meter to check sweep, digital meter to record voltage (both meters grounded at the battery negative post).

 

Yeah I cleaned my IAC really well with throttle body cleaner. Guess I just need to suck it up and get the part because its pretty annoying.