There could be a vacuum leak somewhere causing the engine to idle too fast. It would also cause the engine to run too lean and possibly burn a piston.
might be fuil pump.
The backfiring may be due to intake manifold vacuum leak. Check the torque on the bolts and also check/replace the gasket.
U have a blown head gasket,cracked cylinder head or cracked block.. The white smoke is from water getting into the Exhaust system.
replace timing chain
On my Chevy truck it idles high when its low on antifreeze but if its not that more than likely its usually a vacuum line loose or cracked. good luck.
I have a 2001 chevy venture and I never had any probs. Only thing is the electrical goes out about 180,000 miles
depending on the year some impalas have 6 inch glasspacks
This can be a number of things. What comes to mind first is, if this is an A/T you may have a bad lock-up torque converter, or the solenoid is stuck. If the engine runs and idles great until you put it in drive, this would be my guess.
You might need to change your throttle position sensor.
Probably a bad idle air control valve.
first step check fuel pressure at the rail with a guage
Chances are, you have either a bad lock up solenoid . Or you may have a bad fuel pressure regulator. This is where I would look first