The light was coming on and going off, very intermittent. Dealer put on code reader and says I need to put in new thermostat and an ignition control unit. Temp gauge has never risen over 200 degrees, and everything seems to work fine. Any thoughts?

A flashing SES light is a misfire, and has nothing to do with the thermostat. The ICM, perhaps, but not likely. Mostly likely cause is a bad coil, a bad spark plug wire, a bad spark plug, or possibly a bad injector. Have the engine scanned at autozone next time it flashes. You should see a code that is P030x the x will have a number between 0 and 6. That number is the problem cylinder, zero is random misfire Post up what you find and we will help you correct it.

and dont take your car back to that dealer

With the light coming on and off at times, not necessarily flashing only, there could be a bad thermostat that isn't letting the car heat up quick enough.

ICM'* have gone back and the best test would be a dealer with the proper equipment. I'm hesistant to say that'* bad, but I don't have the equipment to test them.

I finally got codes they say came up
P0128, P0350, P1811 and P1350

Any thoughts?

P0128 is engine coolant temp https://www.gmforum.com/showthread.p...65#post1390947

P0350 I do not have on my list.

P1811 is long shift. https://www.gmforum.com/showthread.p...89#post1429289

P1350 I don't have on my list.

Start with your engine coolant temp, if that'* not reading right it can cause all kinds of strange problems.

A quick Googling showed this:

"P0350 Ignition Coil Primary/Secondary Circuit Malfunction" (random/multiple coils)

P1350, when the car is not cranking, is a dead ICM.

Dan, P1350 seems legit, but you may want to verify P0350 before adding that to your list.