How can you blame the Opti, when the install was incorrect? Basic check before install is the dowel pin length.

I bet that the link to Shoebox's "how to" has been posted in this forum THOUSANDS of times. Buy a cheap repro or rebuilt unit, and install it incorrectly, and you will have problems. Do it right, and the chances of a problem are greatly reduced.

 

I had the same problem. Missing and stalling after it warmed up. The Optispark was replaced 500 miles ago. I remembered the older GM vehicles that started cold but not when hot usally needed a ICM.
So I bought an ICM with no help. I noticed it would try to stall when you stepped on the gas and if it didn't stall, the motor would catch up and run. So I thought a TPS was the answer. NOT!
The only code the scanner gave me was for the temperature sensor. I thought it couldn't possably have anything to do with the motor misfiring etc. Well guess what, I bought a temperature sensor for $14, installed it and the vehicle runs like new. Can anyone explain what the water temperature sensor has to do with ignition problems?

I hope this may save someone who's thinking about the big Optispark job and may not need it.

 

The PCM uses the coolant temp to set the A/F ratio. If it thinks the engine is cold, it richens the mixture. If it isn't really cold, it will run pig rich, misfire and stall. It also uses the coolant temp to put the PCM into closed loop, where it can control the A/F ratio using the learned long term fuel corrections.

Bottom line... without the correct coolant temp input to the PCM, its not going to run very well. Its not causing an ignition problem. Its causing an air/fuel ratio problem.