so when I come to a stop, while foot on brake I feel car self accelarate, RPM needle jumps a little too, waiting for carmax to return my all with an appointment for service. In the meantie, any ideas what can cause this, what should I mention to service tech when I take it in? Any help is greatly appreciated, I am concerned about my baby, 07 HHR.

 

Once they pull the code/codes(if any have been set)it'll give them a much better idea of what's going on, but I have two possibilities jumping to mind. The first would be a defective throttle body assembly causing a fluctuation in idle RPM, the second would be an issue with the accelerator pedal assembly sending a inaccurate output signal to the ECM and causing an RPM fluctuation at idle.

I'd suggest in the meantime that you put the transmission into neutral while waiting at lights to see just how high the RPM will bounce without the torque converter load so you can tell the tech. Also its safer when you have an issue like this in case you have a sudden RPM increase that takes you by surprise causing an accident.

 

thanks!!! Also, I noticed this weird rocking, mild side to side rocking while @ stops, as if a mild earthquake shook car or someone was rocking car side to side from the outside. Happened a few times.....i will mention ur thoughts to tech, thanks again.

 

The 'rocking' while you have your foot on the brake, may be the motor trying to go & can't.

I agree with 843, throw it in Neutral at every stop till this gets sorted out..

 

Hmmm, the rocking when coming to a stop suggests to me that you have either a tire that's out of round maybe with a broken belt in the carcass, or a bent rim. Have them check the wheels and tires while its there, a bent rim can be lived with, a defective tire should be replaced A.S.A.P.

 

843- I read: mild side to side rocking while @ stops

 

Yup, you're right sleeper, sometimes the eyes are not exactly hooked to the brain correctly. I could see the RPM fluctuations causing a rocking sensation in a vehicle with a longitudinal engine, but in a transverse engined vehicle like the HHR, its kind of odd but not beyond the realm of possibility. Purity D, please disregard the thought on the tires/wheels and chalk it up to old eyes on my part.

 

I agree about "fluctuations causing a rocking sensation in a vehicle with a longitudinal engine, but in a transverse engined vehicle like the HHR, its kind of odd"

But just can't think of "what else ?"

 

My "06" has done that forever. A little surge, she wants to run LOL. I have felt that there is no danger, so why take it in. Once you take it in...it will want to return. Mine has never been in for any service whatsoever. Knock on wood! Well, oil changes etc. of course. Todd (Uma)

 

I've been wondering if this was more of a "surging" than a "revs up" which I would say are two different things. Mine has done a surging a few times when stopping for a light and then "rocked" a bit as if it might stall between "surges" (as if that makes sense ) The times it's done this were right after shutting of the AC as I was braking for a light and braking for a light right after accelerating. Both times it was like the computer was doing a "WTF dude, make up your mind".... also both times were before I switched to 93 octane.... hasn't done it since.

May or may not be what the OP is talking about.....