Admittedly, I'm coming onto this thread late in the process. Nevertheless, I'd like to offer some opinions.
1) One post said the car made 380 at the wheels. That is about 464 at the flywheel–which is not bad for a 2-bolt motor which has cams, no headwork and headers. If this car is running as bad as suggested in posts by the OP, those dyno numbers are a bit suspect. The OP stated the "mechanic" said the engine was lean then rich in PE (secondaries enabled). Does this guy have any information more specific than just saying it's "lean" or "rich". If so, post the air-fuel ratio data he recorded during the dyno session. Actually, ask him for all the data from the dyno session and post it here.
2) The very first post states clearly that the engine runs ok after cold start and during early warm-up but once the ECT comes up, the idle stability goes away. Without seeing some serial data, I'm guessing, but I'll bet this engine's fuel trims are whacked when it's at idle/part-throttle in closed loop. It's possible that's because of the cal but, considering the cams are said by others here to not be too radical and it's got one of Haibeck's chips, at this point, I don't think that's probable because, as long as the engine specs, as communitated to Marc, were correct, his cals are usually pretty close.
3) The OP talks about the service engine light coming on. Why hasn't the mechanic involved connected a scan tester to the engine and read any current or history codes in the ECM?
4) I'd be looking at various engine controls components, like oxygen sensors, MAP sensor, vacuum hoses etc.
5)
Quote:
Originally Posted by DRM500RUBYZR-1
(snip)With utmost respect to your current mechanic, I would suggest holding off a bit and going back to check out all of the basics before trying to fix a basic performance problem with an advanced dyno-tune.
Everything that you indicate as a problem, all seem to be simple misfire issues. Fuel or ignition are usually the culprit absent a mechanical problem, which is less probable, as you say it only happens at low RPM.
Look first for simple causes, perhaps multiple simple causes before investing thousands elsewhere.
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"DRM500RUBYZR-1 gets the weekend "Beacon of Reality Award". Please consider his suggestions
6) Run the fuel pressure tests in the Factory Service Manual and post the results.