Weird thing happened to me at work on my lunch break. I went to start up my 1999 xj and turned on the ac and went back in to heat up my lunch and went back, I smelled rich exhaust and checked the dash and saw that it was idling erratically between 250 Rpms to 1400 Rpms with needle wavering real fast, and I turned off the ac. It settled back to normal idle of 750 Rpms within 60 seconds.
I just wanted to make sure so I turned ac back on, and good enough, it started rough idling again.

I know I replaced the throttle position sensor couple weeks ago, (it was a cheap 18 bucks sensor off eBay)

I'm wondering if that got anything to do with the rough idle?

The other symptoms of TPS going bad is still present, such as
-high idle when starting engine
-delayed response when shifting Into reverse
-late shifting timing (3,000-3,400 Rpms)
-inability to downshift while uphill unless I press gas pedal more further.

I'm guessing I probably should have gotten a mopar throttle position sensor.

Do anyone have an input to any other possible causes of this situation?
Many thanks

 

I would also like to add that when I turn on the ac, and before It start idling erratically, I notice that the voltmeter start going to the negative side of the gauge, normally it would be at 14 volts when running without ac on.
The needle move to 9 volts or less, it just stopped moving against the negative end.


I'm wondering if alternator is going bad, could it cause this?

 

I haven't driven the jeep wit ac on yet, I will do that after work and see if the Rpms are messed up while driving.

Maybe it only happen while parked and idling.

 

I bought sensors off eBay and found out they suck, best go to advance or auto zone and get one, u will pay more but its better in the long run, as far as a/c issues my a/c doesn't work in my Cherokee so I have no idea

 

I have a 99. If I have the AC and come to a stop, my volts drop. I assume its because the aux fan is on and my hvac fan is usually on full blast plus whatever draw the AC compressor has (if any). I think the issue could be resolved with better battery cables and possibly a newer higher amperage alternator.

BUT

If you're having symptoms of a bad TPS those could be completely seperate.

 

The IAC is supposed to adjust/hold idle speed to compensate for AC load on the engine.

 

It already have 124 amp alternator and all the battery cables are upgraded to 2 AWG 6 months ago.

I guess I ll have to get a better TPS and a new IAC

 

Update... I decided to get a mopar TPS off eBay to replace the cheap one I got from eBay and its running normal now!

I guess I can't trust those parts eBay sell for 10 bucks. It's too good to be true lol.
I also cleaned the IAC. No more rough idle.

 

Glad you got her working. I've made the mistake of getting parts off amazon and eBay before. Never again. Better off just buying stuff from the parts store and be able to return it easily if its bad.

Only place I really trust online that is cheap is rockauto.com.