Ok, here's the thing. I have an LS1 supercharged & intercooled setup. It is running very badly with a 2.5-bar MAP sensor & custom OS. I have followed the Custom OS Tutorial & applied all the relevant mods (including the MAP sensor calibration, which reads correct against a barometer - we are approx sea level here in the UK).

It idles ok & pulls away fine but when I floor the accelerator pedal, it coughs & jerks until I back off the throttle . I can accelerate fairly smothly if I go easy on the pedal.

It is pulling timing when the problem occurs (as far as I could see with ScanTool).

I am going to try a few things tomorrow (having read some of the threads in this forum). I have added the GM.DYNCYLAIR_DMA & GM.CYLAIR_DMA PIDS to the dashboard for logging & will do a run before making any mods to the tune file.

Has anyone got any pointers or suggestions (or even had a simialr experience)? Any help gratefully received.

Ta!