When I turn my air on to any setting other than dashboard or feet my rpm's jump up. It does this warm or cold, park or drive. The ac compressor is unplugged and has been for some time. But the revving issue is relatively new. I do have an electrical gremlin somewhere that keeps popin o2 sensors.... I've replaced both the up and downstream twice now...

 

Check your IAC (idle air control). Just had the same problem a few weeks ago on my 99.

 

....what kind of 02 sensors (brand name) ...

 

...haha.. Your the second person to ask what brand.. Idk but they ain't cheap! Just went and unplugged my iac and ran it for a couple miles. So far it's better than with it plugged in.. Not as hard a kick when I shift into gear (aw4). And smoother idle when driving with foot off gas. HOWEVER... it still did the weird hesitation thing it's been doing. So I'm thinking new iac and another set of o2's. At least the o2's are under warranty and will be free. I'm gonna go see what happens when I turn the air on...

 

Just tried turning the air on different settings with the iac both plugged and unplugged. Now it's not doing the higher rev thing... Idk.. I'm gonna buy one tomorrow and see what happens.

 

DON'T BUY ANYTHING UNLESS YOU HAVE A CODE FOR IT!! You're wasting money.

Do a search for Bosch 02 sensors for a cherokee, then search for NTK. If you have on that looks like Bosch, regardless of code or no code, toss it and get the NTK.

You can get the NTK version at NAPA. Don't use anything other than NTK. Just do a search for either 02 and you'll see. I've covered this ground already.

ALSO, if your RPM's go up when you turn the AC on, you have a vacuum leak after the AC **** itself (the one that turns the air on and off, points it to the floor/defrost). If you disassemble that assembly panel and look at the ****, you'll see there are many vacuum lines (small flexible rubber hoses of varying colors of the rainbow... and black). The black one runs out through the firewall. on the passenger side. It should be up above the blower motor, and it connects to the only other vacuum line that runs right through there. That's the BLACK vacuum line on the ****. The fact that the RPM's go up AFTER you turn on the air indicated that the black vacuum line that runs to the **** is just fine. HOWEVER, the OTHER vacuums are suspect.

NOW... do ALL of them give you an increase in RPM or just certain ones? The ones that do would be the ones leaking vacuum.

 

Good lookin out on the Bosch o2's! The rpm's increase when on all settings except feet and upper vents. I have looked over the vac lines some and found nothing obvious. I'll have to check behind the panel at the switch it's self. Had the resistor changed out a few months ago, just FYI...

 

VTJeep-check the vacuum line by the battery tray while ur at it. I have a 99' with 137K on it and my vac live was rotted out there, only allowing the A/C to come out the defrost vent

 

That one was disco. when I got it and we promptly hooked it up. Another thing is the whistle that only happens at certain like 30-50% throttle. I've been told it's a bolt or two under the manifold that just need to be tightened a bit. Any way this is causing it? So I plugged the iac valve back in and it's running better for now. I'll get the codes cleared and scanned again before making any major purchases.

 

I've got a bunch of vacuum leaks too, what size is the hard plastic vacuum line going to the vacuum ball and under the battery tray?