I have an 88 park avenue that will start fine cold, after running 5 minutes the check engine light goes on, if I stop the car and put in park, idle speed is very fast. If I shut it off in this condition, it wil not start, let it sit for 6-8 hours, it used to start up again- now it wont even start, just runs a few seconds then dies. The code is a 21-throttle position sensor. I have changed: (hang on) the IAC valve, TPS sensor, cam sensor, crank sensor, egr valve, coolant temp sensor, swapped the ECM with another the park ave, fuel pressure regulator, oxygen sensor.
I have checked and do have spark, also have fuel in the fuel rail. mass airlflow sensor was swapped with a working car as well.

Couple other items to note, while the light is on, the cooling fan does not kick in, the air conditioner may not cool during this time. :banghead:

any ideas?

It looks like most of the sensors have been checked, so the high idle could be from a possible vacuum leak. Some are a pain to find. However, I have a 90 Electra that had the same problem with not turning back on after I cut off the ignition. I changed all of my sensors, no joke. It put a serious hurt on my wallet. I even replaced the entire fuel system, excluding the injectors. Fuel was in the rail and everything. When I finally broke down and took it to the mechanic, it turns out the the baffle on one side of the fuel tank was stuck causing fuel to slowly leak toward the New Pump, which i didn't need. So, fuel would come back to the pump after sitting a few hours. Just enough to let the car run for a few seconds. Best thing is to use a fuel pressure gauge and keep a close eye on it while trying to restart the car. Could save you hundreds of dollars.