misfire

I have a 2001 Buick LeSabre 3.8L and have been getting a P0302 code. I have replaced the plugs and wires, changed the coil packs, changed the fuel injectors, checked fuel pressure and compression test. I changed the valve springs. I never got the code to change cylinders. The misfire only occurs in overdrive @ low RPMS and on full accelertion. On cold start the misfire can be felt as well. I have a plastic intake manifold which I have heard can cause problems with these engines. I have not changed the ECM yet, can anyone let me know if this is a good option or if there is any other things to check or change before I change the EMC. Thanks.

Welcome to AF. How does the plug look on #2. You replaced the injectors? Do a scan and look at fuel trims?

I have 2000 Lesabre 3.8 that I just got the misfire code on the eway the other day. It shuttered, the check engine light flashed then went on steady and engine smoothed out. A mechanic looked at the spark pl wires and said they were original and old. I rep plugs and wires $200 and it appears to be running ok. I gut tells me something else happened I just dont know. This week end I plan on unpluging things and checking for corrosion.