Check engine light, can't read codes
 

Working on A/C compressor swap, went to start car,it idled fine, went out to test drive. Car ran rough would rev to 1500 rpms and missing left and right. Set check engine light. Went back to house, turned car off. Car took long time to start, idled fine. Could not communicate with car from laptop I just used last Saturday. Cigarette lighter is working. Took car to a friends garage, it drove fine, but check engine light is on and fans running all the time. My friend has the top of the line Snap On scan tool. His scan tool cannot communicate with my car also. So I think its opti or wiring harness. I did move the opti harness where it connects to the engine wiring harness which is mid intake manifold. So what else can I do to diagnose this. I do have a new opti, but would like to diagnose the problem and replace only whats needed. I was going to replace the opti wiring harness first and check those connections. But cannot figure why I cannot talk to the PCM. Any help would be appreciated.


tia

Andy Schuck