I've been fighting a similar issue for a while but mine misfires only on a light load, right before lockup. Engine light flashes, random misfire code and no lockup. Can't trace it down.

 

Warmed up would be closed loop(running off the O2 sensors). Have you done any logging for your tuner so he can see what is going on? Any change to the idle if you unplug the MAF?

 

My opinion, given that I had the same issue for quite a while until I had someone really take time with it - its in the tune. Need to step up the timing just a tick when the throttle is getting feathered. I had my issue at 50-55mph when I just barely applied the throttle - couldn't get it to go away with plugs, vacuum checks, fuel addatives...Alvin @ PCM of NC solved it. Runs like a beast...

 

changed the pcv and seem to solve the idle problem for the most part. the missfires dont seem to be reading at idle anymore. did my tank of 93 an 89 and its still pulling timing. im gonna plug in my stock pcm and see if it still does

 

but at idle it still will shake/kinda missfire feel but no codes or missfires on the data log.

 

Do you have a cam? Anymore aftermarket goodies other than a tune?

 

negative. flowmasters and tune. the rough idle is kinda intermittently. sometimes it idles smooth, then it will have that missfire feel.

 

So it is misfiring or just has the feel/sound like its misfiring? I would say certainly check the tune.

 

Have you checked your coils? I had one that was intermittently missing. It would cause rough idle and part throttle problems but WOT was fine. I used an infrared temp gun on the exhaust primaries and found one a lot lower temp then the rest. That was the bad one. Been fine now for 3 years.

 

gonna check put the stock pcm back in this week and check. not a bad idea ill see if i can get a way to do that