Car starts, warms up, and as it warms up to operating temperature the idle begins to fluctuate and bounce back and forth between 800rpm & 200rpm, and eventually it stalls out.
Fine while driving around as long as revs kept above 1000rpm.
We’ve replaced MAP sensor, coolant temp sensor and thermostat, throttle body, accel pedal and sensor, coil and ICM, cleaned injectors, new air filter, oil and oil filter, trans fluid and filter, and inspected hoses and intake for vacuum leaks using carb cleaner spray method. Replaced the computer and had it re-flashed. Pulled the plugs and they are fine and gapped correctly. Tested fuel pressure at rail and it is fine.
Nothing is working to solve this and I have no new codes or CEL showing.
Tomorrow I’m pulling the O2 sensors, cleaning, and re-installing, pulling the fuse bank, cleaning contacts, and reinstalling with dialectric grease. Also going to pull the alternator connector, clean, and dialectric grease.
Other considerations are the crankshaft position sensor, timing chain and tensioner, and body electrical ground straps. Trying to fit it all in tomorrow.
I have also had two other pro mechanics look at it all, and use a $7k scam tool and they also really didn’t know what is going on. One of them is my mother’s fiancé and he ended up finding a computer from another HHR and then having it reflashed at a local Chevy dealer.
Nothing seems to be fixing the issue. It is very frustrating.