I have 2002 chevy avalanche, check engine light comes on only when its cold & runs rough at idle. When warmer weather light goes off & runs fine. Have replaced mass air flow sensor.

emissions tend to freeze up in cold weather.. some folks block the extremely cold air up front with a disposable cardboard sheet.. this allows the motor to run warmer..you may need to do this..some cars have a space betweenthe radiator and the ac condenser to slide a sheet in there..otherwise it goes in front of the grille..

Leaking intake manifold (vacuum )

check airflow meter isn't sticking

-Check for misefire.

mai

sounds like a sensor is loose maybe not have good contacts?

check Idle speed motor

check your glow plug relay! located on the right side head

The clamp bolt in the center of the steering column put a small cut in the #5 ignition wire and sent the code to the computer for multiple ignition failures(I forget exactly the terminology that they used and what code; I think it was 0300). The arching must have told the computer to richen up the mixture because you could smell raw fuel. I replaced the wires and ran a can of Seafoam through one of the vacuum lines(brake booster) and all seems well. If I had listened to everything I read at other websites I would have been replacing the Cats and the Ignition Coils-very expensive items. Instead it cost me $50 for a set of wires.

I hate to be the barer of bad news, but may be the head gasket.

My car started with rough idle. Then very hard to start in cold weather. Next started overheating, but no output from heater. Trickling sound from behind dash board. Overflow bottle overflowing.......

I replaced the water pump, radiator cap, thermostat, coolant, fan belts, power flushed the system. Nothing worked. Some research gave me the answer.

The head gasket leak was allowing exhaust gases to enter the cooling system, displacing the coolant. After use, as engine cools, coolant is sucked back into the system and coolant seeps into the cylinder. This gets worse over time.

First thing you'll notice is the rough idle as the spark plug burns off the coolant in the cylinder. (This is especially true at low temperatures.) If it is the head gasket, the other symptoms will follow as time goes by.

Spark plugs/wires might need to be replaced. Check your spark plug gaps and check your spark plug module harness connection on both sides of the engine. The check engine blinking indicates short/misfiring. If there is short in the harness, you can check it by moving around the wires close to connector one by one while the engine is running. You might need to remove and ckean the Throttle Body.