You've probably got a vacuum leak under your throttle body. I have an 88 c1500 with the 4.3 and it idled at over 1000 rpm all the time. Found out that it was a bad gasket between the t.b. and the intake manifold. It took about 20 minutes to replace and it idled beautifully afterward. Grab a can of carb cleaner too, it prolly wouldn't hurt.
It could also be the IDLE AIR CONTROL VALVE, easy to change, cost about 45 bucks at your local auto parts store.
Either the fuel mix is adjusted wrong or the carb is dirty
its a vacumn hose issue,,,need to look for a cracked hose at the rear of the motor,,down about half way .
vacuum leak.
wiper motor or the bolts holding it tight.
The timing is too low or it has the wrong spark plugs in it.
It really depends on the make/model of your car. Suspects include: Idle Stepper Motor/control valve, engine CPU, fouled injectors, incorrect spark plugs
blower resistor is bad
I have a 2003 astro with the same problem, it was the blower motor
U have a blown head gasket,cracked cylinder head or cracked block.. The white smoke is from water getting into the Exhaust system.
The fan relay could be bad or the fan motor could be bad.
Replace the paulse board that's attached to the wiper motor.
On 03 silverados i belive the blower motor relay is internal to the blower motor resistor. i could be wrong though, check the underhood fuse/relay panel for one.