4.3 Vortec, choke problem?

My 1996 4x4 Sierra will start up fine, after a minute or two will idle down and run very rough (no smoke like flooding) but after a few minutes more will smooth out. This started happening in the spring when warmer weather began. Any ideas?

My 1996 4x4 Sierra will start up fine, after a minute or two will idle down and run very rough (no smoke like flooding) but after a few minutes more will smooth out. This started happening in the spring when warmer weather began. Any ideas?

Welcome to AF on your first post.
It does not really have a choke.
A good tune up may be in store fore it.
What is the mileage and service history?
Check engine lights?
Watch and check that fuel pressure and also check VCM sensor readings
The eng and intake air tempt sensors can cause rich running.
MT

Welcome to AF on your first post.
It does not really have a choke.
A good tune up may be in store fore it.
What is the mileage and service history?
Check engine lights?
Watch and check that fuel pressure and also check VCM sensor readings
The eng and intake air tempt sensors can cause rich running.
MT

156,000 miles, just did total tune-up last fall including plugs, wires, filters, a couple O2 sensors, also recent new fuel pum, filters, checked fuel pressure at 64 lbs.

156,000 miles, just did total tune-up last fall including plugs, wires, filters, a couple O2 sensors, also recent new fuel pum, filters, checked fuel pressure at 64 lbs.

Get it on a good scanner and see if anything shows up.
Run a injector balance test on it.
Good AC-Delco plugs right?
And watch that fuel pressure for a fast leak down.

Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.

Mt-2500 Thanks For The Help, Will Check It Out

a bad coolant temp sensor will cause these symtoms also