engine misfire

[tomm]

My 92 SHO (mtx) with 215k miles is misfiring. The CEL light came on after less that 2 miles of driving yesterday. The idle drops to 600rpm and the AC shuts off while the CEL is on. The other day I drove for about 60 minutes before the CEL came on yesterday it was on in less than 10 minutes. The tach swings erratically if I accelerate past 3K rpm. Performance seems to improve when the secondary intake runners open up ( I can't detect the miss but a higher rpm that might be difficult if only one cylinder is involved) but the CEL is still on. Sometimes at idle the CEL will go out and then come back on when I touch the accelerator. The last tune up (plug change and plug wires) was at 191K. Recently I had the AC Compressor and AC lines replaced. Any thoughts, Help! I don't want to get in over my head again like I did on the AC.

 

[93rev2sev]

When was the last time the MAF sensor was cleaned?

If your Tach is going haywire, check for a bad ground; from the DIS to the firewall, especially

 

[tomm]

Thanks,

appreciate your response. The cel and misfires only occur when the engine starts to warm up i.e. after being driven 6 to 8 minutes. I have never cleaned the MAF sensor properly, I have cleaned the intake of the throttle body but nothing more.
I went to Advance Auto today to pull the error codes but their code reader failed to function with my SHO, it would not start the analysis to read the codes. So I am at a loss.