Just got a dyno tune but still having this issue. It was getting late and my mechanic already had 6 hours in on it yesterday. It's understandable that he wants to visit this issue later but I'm hoping someone here can help.
LS1 conversion into 89 GTA, Performabuilt lvl 2 4l60e with Edge 3,600 stall, Torquer v2, Prc 5.3 stage 2.5 heads, Hawk's 1 and 3/4 headers into 3" collectors, LS6 intake 60 lb injectors, 340 fp, pulley, p/p throttle body. Speed density tune. Made 425 rwhp and 382 tq, converter locked, pulls hard to 6,700 rpm (see dyno sheet), and runs great EXCEPT surges then stalls out if revved in N or park and then suddenly off throttle. Seems to do ok when throttle transitions are slow. Sucks to turn a corner, touch gas lightly then off to come to stop or sudden turn and then have it die. Idles great at about 850 unless you rev it lightly and then let off. That results in surging and stall out also. Mechanic says readings don't make sense and he wonders if the person that ported the tb didn't mess something up.
Originally he suspected it was the maf when it was still on a maf tune. I bought a new maf and it seemed to be better for a day or so. It is now on a speed density tune and the problem is unchanged.
He wanted to rule out a vacuum issue so blocked off the vac to the fp regulator and has the computer relying on intake manifold pressure (map?). No change.
It is the only major issue remaining. If anyone has a clue please chime in. Can't take it to the track yet because I know it will die after a burn out and then probably load up on the line.
One more thing. I built the car for my Dad who now owns the car for the third time. He had it in stand still traffic one day that it was about 85 degrees. After several minutes standing it dies and took nearly 2 minutes to restart. It repeated this behavior on him later the same day under nearly identical circumstances.
It would bother me less if it was happening to me.

 

1. A 425rwhp build with a TQ v2 doesn't need a SD tune or 60 lb injectors.
2. Without seeing the tune or a data log how could anyone know what the issue is?
3.Yes if the TB was overported and the IACs are at 0, that could be the problem,but then again without a data log showing the IAC value, who knows.

 

The 340 fuel pump, fuel pressure regulator, and 60 lb injectors were done in anticipation of a supercharger in the near future. Tracey usually can get more out a SD tune and the issue exists regardless of speed density or maf tune.
I can check with him and see if he will post up the data log.