2001 GSR, recently the car died on me randomly, no spark at all, so my local shop diagnosed it was the ICM and replaced it.
Upon driving the car home, it had a CEL [P1607 Engine/Powertrain Control Module Internal Circuit Malfunction] which I cleared.
The CEL never came back, but I immediately noticed a lack of low end power and VTEC was much less pronounced or noticeable at the 4400 RPM crossover.
It's had a buddy club spec 2 catback for almost 10 years, so the change in power / sound is extremely apparent. VTEC used to hit nicely at the crossover, now it's almost completely inaudible and there is no real power until the butterfly runners open at 5800 rpm (which I can now hear since the exhaust is so much quieter - before the exhaust would be louder than the intake in VTEC).
I tested a p28 ECU w/ a stock GSR basemap on it to see if the ECU was the issue, but it runs the same as the stock p72 ECU.
I'm thinking my ignition timing changed when they took my dizzy apart to replace the ICM? I'm struggling to understand how just replacing the ICM would have such an effect on the engine.
Any ideas/insight would be much appreciated. Cheers