I have an LS2 in a 56 Chevy with a 4L65E automatic transmision. I noticed that from a stop I will give it enough gas to stay in first gear and before it goes into second, i will let off the pedal and just coast the car. When I do this the engine begins to surge up/down, up/down until the car comes to a stop, then the engine idles fine again. I have tried manualy swithing to second when the engine is surging and then it will idle fine. It seems it only does it when coasting in first gear. other than this glitch, the motor runs great. What could be causing the surge when I coast the car in first gear?

 

How was it tuned ? Sounds like the idle IAC values need tweaked. Or a possible vacuum leak, but if it does not do it in other gears, prolly no vac leak?

 

I have a set up from Painless Wiring that runs one ECM for both engine and trans. They use an LS1 ECM for this. The ECM was flashed by them and I haven't done any fine tuning yet. Someone told me to try a hotter plug in the engine, that it would help out a lot. Has any one heard of that? Thinking of maybe getting the software from HPtuners to help me tune the engine.
Thanks.

 

Tune it.