1990 3.1 No Start Problem

My 1990 Grand Prix LE, 3.1 will not start!!! It turns over normally but will never start. Originally it was an intermittant problem but I haven't been able to start it for a week now. I took it to the dealership last month when it started acting up and of course it started for them everytime. I left it there for 3 days. They said they scanned it and showed no problems. They did reset the idle speed and it had no problems for a month until last week. The check engine light is on but it will not go into diagnostic mode with a handheld scanner. It never blinks. When I can get the car to start it will go into diagnostic mode but doesn't show any codes. I have had this car a year and replaced the computer and prom, fuel pump relay, map sensor, battery, fuel filter, and ignition module. The plugs have spark. You can hear the fuel pump running. It has plenty of gas. It has about 85,000 miles on it. When I was able to start it, it ran fine and would restart with no problems. It would sit overnight and be a no start again. I called a mechanic and he said that it could be plenty of things and would cost a fortune for him to keep it and go thru it. I can't afford that. Is there anything I can check on my own to kinda narrow down the search? Any suggestions would be helpful. Thanks.

this might sound like a stupid question but are all the wires tight? like the wires at the battery termnals and wires on the starter?

Yes, I have checked all of the wires.

Have had same hard start problem when cold with 88 gp after lots of coding etc., tech cleaned contacts at temperature sensor, located just below the thermastat housing. 2 minute fix.

Iac ?

This sounds exactly like a problem I've had on all 3 of the Grand Prix I've owned, except I didn't have spark. So this is just a guess. It was the ignition control module located behind the coil packs. They always started to go bad on me in the winter. I wouldn't start occasionally but other days it was fine. This is sort of an expensive item about $80 at autozone. I see them on ebay all the time so I would try to pick one up off of there if you're troubleshooting. Hope that helps.

try the crank position sensor in the back of the block first, it's a simple job and relatively cheap. IF that doesn't fix it, it's more likely than not an ignition module, which is expensive and a ROYAL PAIN to change.

or it could be an egr valve too, or the check valve for the fuel pump.