Ok well its winter here with the -30s haha.. soo evry morning I Let my Monte Warm up for 10-15 mins... When i get into the car I notice the RPM gage JUST A JUMPING from 500-2500rpm.. but will settel down. Kinda like when you turn everything on in your car and it will Jump up and down because your useing power I think.. Soo im just ceriouse what could cause this to happen?? Once i start driving it never will Jump again. My Car shows the code for rear 02 sensor.. Could this Be because my cat is pluged and putting back pressure out??

2005 / SS / Just rolled over 75 000KM



** I Noticed*** this only Happens Once I put Car In Gear Revers or drive. and Do not Step on the Gas. Once I give it some gas its goes away.***

 

Sounds like the car is hunting for its idle speed. Bad o2 could cause this, also a dirty IAC(Idle Air control valve) can cause this too. I would clean the throttle body and IAC valve and port it goes into, then go from there.

 

could be the bad O2 sensor. If your already showing a code for a bad rear O2 sensor, i'd fix that, and go from there.

Its possible it could be a bad cat. But first fix the O2 sensor.

 

well even if i get the DP with hi-flow theirs no reason for me to change 02? the 02 sensor would tell my car to juggle rpms? once dp in code will show.

 

If you have a vacuum leak, from either an intake\throttle body gasket or vacuum line, it will cause your RPM's to jump up and down too.