Ok.

 

Ok so I took the car to the local Interstate Battery store and they checked the battery. It showed a 70% charge and tested OK for cold crank capability. Not recall the exact value but something like 166. I explained that the car is sensitive to low battery voltage and priced a new battery. The clerk pointed out that the battery is only 2 years old (I did not know that as have only owned this for a 6 months) and if not run frequently perhaps just needs a trickle charge and he dissuaded me from buying a new battery. I got home and put my smart charger on it which indicated a 50% charge so I left it on overnight. Battery fully charged to 100% this morning. Started the engine and same issue of start/rough & stumble/rev up and drop to good idle. So I have just made an appointment at a GMC dealership that I have used in the past and have had good service from. I will report back what if anything they are able to determine. Have given them the list of items replaced and all the symptoms so I am hoping at long last to get this thing resolved. Oh, and by the way I reported earlier in this thread that I did rent a fuel pressure gauge and got good readings.

 

My recommendation for the fuel pressure test was for Lonwane.

 

Local dealership has had the car for 24 hours now and no word yet from them! :) In a way that makes me feel better that perhaps this problem is stumping the "experts" but I will soon start to dread the "not a simple fix" situation $$$$$ :)

Update Friday 4 Sep: Just got a call from the dealership Service Dept. They have been unable to determine the problem thus far. The tech suspects fuel pump or injector(s) but they need to keep the car until next week. I said fine! :)

 

Update Tuesday 22 Sep: Called Service Dept today to see what the status of my car is and was told they replaced the injectors which had to be ordered and took a while to arrive. Still has the problem however and tech is now in conversation with GM via phone trying to figure out a solution.

 

Good evening, I'm looking to see if your issues were resolved, My 2007 hhr is doing the same thing with the rough start, choppy idle then high rev and back to smooth. It's been driving me nuts and I want to get it fixed! have a good evening!

 

sky sailor, if they are just throwing parts at it until it’s fixed, the shouldn’t be charging you for those injectors, they should be reinstalling the original ones. Fluctuating idle and running rough , have they inspected the throttle body? Or the MAF sensor? Any vacuum leaks around the intake manifold, the power brake booster hose loose or the fitting cracked ? Many possibilities.

 

Nothing to report yet. I called them today for an update and the service manager was out so left a voive mail message. Someone called me in reply to my voicemail and said they would have the service manager call me when they returned in an hour or so but...no call back today! I will call again tomorrow. Obviously they are flummoxed by the problem. I will certainly report the outcome when it happens! :)

 

I am in agreement Oldblue. Sounds like the injectors did not do the trick and they are scratching their heads over this. If a dealership can't solve this I don't know what to do. BTW prior to going to the dealership I replaced: MAP sensor, MAF sensor, Throttle-body, Accelerator pedal/sensor assembly, air filter. The intake and exhaust VVT solenoids were replaced just before I purchased the car. Hoping very much that they will sort this out so have not been rushing them on the issue and the car is a tow-behind for our RV so have not needed to have it these past few weeks. Cheers.

 

ShorgiunRuml and Oldblue - I just got off the phone with the service manager. He tells me three of my injectors had low voltage when running so they were replaced and says the idle is now fine but...the funky rough idle, rev up and smooth down stuff is still happening and they are unable to determine the cause without any codes being thrown. I asked about their phone call to GM corporate and he said they were initially trying to help figure out the problem until they learned the title on this vehicle is a salvage title and then they washed their hands of the whole thing. Service manager says he can't do any more other than spending hours (billable of course) and hours tracing the harness and connectors. I will be picking the vehicle up later today. BTW I explained to the service manager that the car was totaled by the insurance company when it was a year old with 6K miles on it. The 2nd owner drove the repaired/rebuilt vehicle from then up to when it had 80K miles on it without issue. I figured it was a safe purchase given its history.

ShorgiunRuml if you find a solution please advise and I will do the same. I may change out the purge valve because although I removed and checked it for proper operation I did not replace it with new. Just another stab in the dark!