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RPM Fluctuate wildly at idle.

5.6K views 5 replies 5 participants last post by  Sandstone  
#1 ·
Hey all.
I will attach a video of the instrument cluster showing the RPM bouncing all over the place.

It feels like I've thrown everything and the kitchen sink at my 2012 Jeep Compass 2.4L CVT. To no avail.
My problem is an extremely rough idle caused by fluctuating RPM. The problem mostly only occurs when the AC is on (or climate control is set to the windshield defroster, which runs the AC compressor to blow dry air).

I'll list below all of other repairs and replacements I have already attempted to resolve this matter.

I guess by pinpointing that the issue is most noticeable with AC on, I should probably just go ahead and get the compressor replaced, but I'm hoping somebody will have some other advice as that is going to be a costly repair. Also worth noting that the AC condenser appears to be pretty beat up from road debris. No signs of leaking but about 35% of the fins are totally bent outta shape. Local AC shop is quoting me ~$1600 to replace the condenser and compressor and to refill with CVT fluid (condenser is double duty trans cooler).

Anyways, here is my list of completed repairs, in no specific order.

Throttle body cleaned.
Throttle body replaced (cleaning showed no improvement).
Spark plugs replaced.
Ignition coils replaced.
Fuel injectors replaced.
Air filters replaced.
Coolant temperature sensor replaced.
Camshaft position A sensor replaced.
Camshaft position B sensor replaced.
Crankshaft position sensor replaced.
Radiator replaced.
Coolant flushed.
Climate control blower motor replaced.
Blower motor resistor replaced.
Blend door actuator replaced.
Idle air control valve replaced.
MAP sensor replaced.
Rear differential fluid serviced.
CVT transmission fluid change.
Serpentine belt replaced.

Despite all this work. I still have a persistent RPM fluctuation.

I understand that replacing motor+tranny mounts will make the vibration less noticable, but it still doesn't address the RPM issue. Sometimes the fluctuations are so bad that it feels like the car is going to stall itself.

Please let me know if there is any other service than AC compresser+condenser replacement that you might recommend. Thanks!!!
 
#2 · (Edited)
Out of that whole list of things that you replaced, only a couple of them could actually affect your idle speed... have you checked for any stored codes? Are there any lights on on the dash?

Might be time to take to a shop for a diagnosis instead of continuing to fire the parts cannon at it.
 
#3 ·
It could be a vacuum leak causing the issue. When I removed and cleaned my intake manifold, I could see that that o-ring gasket was just starting to fail along the bottom center section. A good way to check for vacuum leaks is to spray carb or brake clean along the intake to head mounting point while idling and see if it smooths out. Also spray where the throttle body mount to the intake and any vacuum lines/hoses, pcv, brake booster, etc.