My engine hesitates when slow but is ok when floored then goes back to hesitating again ,worse when cold, 97 gmc safari 4.3 awd

Have they given you the code for the service light?

MIL on? Plugs, wires, dist cap & rotor, MAF sensor, hard to say with such a vague statement.

Yes the egr valve could cause starting problems. If it is sticking open it would cause a huge vac leak.
I would want to know what the trouble codes are in the computer first. Those codes would help a mechanic nail down the problem area and what to check.

ENGINE COULD HAVE THROWED ROD BEARING.REMOVE SPARK PLUGS TO KILL COMPRESSION WHILE YOU TURN ENGINE OVER.IF ENGINE STILL WONT TURN EASILY VALVES LASH ADJUSTMENT COULD BE TIGHT MAKING HARD FOR ENGINE TO CRANK.

sounds like fuel filter or garbage in your tank

need to have it scann for engine codes to know whats wrong it could be lot stufff.it could be injecter, computer,plugs,plugswires,coil packs,or just coils, a weak fuel pump.

Probably will have to replace starter if you bendix is sticking. Easy DIY and not too expensive...

Did you check earth connection of electric system?

sounds like the car either has a problem getting fuel, air or spark. mechanics can run diagnostics on it to pinpoint the issue.

This light is telling you that a problem exists in the AWD system, the light reset's everytime the key is turned off, then because the system fault s still there it comes back on, the 20 second delay is the time required for the system to test itself.