I am beyond confused right now. I have been chasing a cylinder 1 misfire for about 3 months now. I have replaced the EGR, cleaned the throttle body and maf, swapped all plugs and boots, put a whole new plug and coil pack on cylinder 1, switched injectors with 1/2 multiple times with no change, and swapped the entire engine wiring harness. I have all but given up recently as I am out of Ideas and I think y'all have been as well after the last two posts I've made. I was about to take it to a reputable shop in San Antonio but while saving up the funding for that (on broke college kid budget) my A/C went out. I went ahead and swapped out the compressor, accumulator, and orifice, and today got it charged. Now when the compressor is on it runs as smooth as a top, I mean you could play jenga on the hood. But as soon as you turn off the a/c it idles rough again. What in the world? At this point I have no DTC's and all tests are done that would display DTC's. What is the deal?

 

I can't offer much help, but it sounds to me as if there may be a mechanical problem in that cylinder. Such as maybe a valve problem. It may not be seating properly and causing compression loss in the cylinder. May need to do a compression test.

 

If this were the case, it would do it with the A/C on as well.

The PCM/ECU bumps the idle up a notch when the A/C is turned on. I think it does this by opening the throttle body plate.

So, could it be that the throttle body is dirty? Have you cleaned it recently?

 

That is true. Thanks.

My truck kind of does this too. Not so much a rough idle, but a bit of a shake when the A/C is off. Smoothes completely under load of the A/C.

 

yes I have, spring break (mid march) when all of my problems started

 

I would suggest getting a tuner and bumping the idle up 50-75rpms. Before tuning my truck idled at at 525rpms and always had a shake. With the tune, the idle is at 600rpms with AC off and 640 with AC on. No shake and runs great.

 

I'll definitely look into that! sounds exactly like my truck. I see you have an sct tuner, how do you like it?

 

I have only used the SCT with the custom tunes from 5star. Mike wrote the custom idle speed into his 87 perf/tow tune at my request. Very happy with his tunes.

 

This is puzzling to me; while a tuner can be used to adjust the idle, it is being used as a band-aid to compensate for the cylinder 1 misfire. This I believe is the cause for the rough or low idle.

 

that's a good point. Help me out bucko! you seem to have answers for problems!