I tried the search function but didn't find anything close to what I'm seeing.

First of this is a 2000 Sport, 4.0, A/C, automatic tranny, 4.5 in lift, clearing 33x9.50s .

This is also my first XJ, so I'm not familiar with their subtle nuances, my other Jeep is a CJ. I've only had the XJ for about a week.

What happens is when any part of the heat/AC system is on the engine will, almost rhythmically every few seconds, rev up about and extra 200-300 RPM. When it does it I hear a click like something is engaging, I was thinking that it may be the AC unit, but would it even engage when the heater is on? When the Heat/AC controls are set to off the engine idles normally with no fluctuation. It mainly concerns me because when I'm braking and the engine revs like this it sometimes catches me by surprise and I have to brake a little harder, plus it can't be doing anything for my mileage. I was also thinking that it may be the alt coming under load, but my volt gauge never moves from just under 14.

Thanks in advance for any help.

 

When you say heat, are you putting it in defrost mode? If so, this will cycle the AC compressor to help remove humidity from the vehicle.

 

I'll have to double check that. Thanks.

 

hmmm I removed my ac, so I am not sure if this will help, but I was having reving issues, but with other symptoms, I relized my vacum lines were messed up, just a thought

 

if its revin so its effecting braking you probably need a new IAC

its not compensating fast enough to keep it from revving

 

sorry i completely missed the reving when braking bit, mine does that, lol I found the vacum line that was leaking and stuck a bolt in it, lol I know getto, but it worked.