The car: 1995 FIrebird Trans-Am, 5.7L LT1. Engine is from 1996 Caprice. Rest of car is stock.
What's happening:
When cold: seems to idle well enough and can push the pedal and get power that one should expect with this car. Drives and accelerates well in all gears. Will go sideways if not careful
. While cool/cold, it rarely stumbles or misses
until car is warm, temp gauge starts moving to normal operating temps.
When warmed up: car will stumble from 0-35 or so and may miss if given too much pedal. On the highway, typically bogs down when accelerating from low RPMs - like 55 MPH and need to get to 60-65 MPH it's almost mandatory to downshift and achieve higher RPMs in order to have the requisite power to accelerate properly. The longer the car driven the worse the performance, it seems, though it's a pretty consistent level of suck when car is fully warm. Does not overheat. Fans kick on as they should.
What's been done:
2010, last 3 months: Pontiac dealer diagnosed DOA alternator, leak in cooling system. Fixed. Asked them to diagnose the tuning/stumbling problem and they said do the distributor/optispark/cap/rotor stuff. Not for eleventy-million dollars at their shop, no. Also should be noted that most or all of those spark-related things were done in a shop in 2007 (see below). Coolant-system flush, Oil-change.
2010, in the last 6 months (car sat for 2 years or so): new plugs, wires, PCV, EGR valve, EVAP purge control solenoid, Alternator, Battery, ECU/PCM, Oil Pressure sensor.
2008-2010: car sat after needing trans work (lost 3rd gear).
Mid-2007 a shop did: Plugs, Air duct assembly 25147186, Hose 9807, Seal assembly 10217886, Seal35072, TPS Sensor 2-19072, Dist & ign kit RR218 (Note: RR = Refurbished? I hope not but maybe so! Grrr). Drove okay but problem persisted - the shop tech could never solve the low-RPM stumbling issue.
Early-2007: Removed stock 1995 Firebird LT1, installed 1996 LT1 from Caprice. Fuel pump (used) was replaced at engine swap time, Starter.
Technology: It was suggested that I get the cable and software to connect to my car through a laptop. Have cable (AKM Electronics), DataMaster software, and being somewhat of a computer guy the Laptop was the easy part. I've recorded some data including a.) cold start to warm idle, b.) various closed loop driving conditions - backroads, highways, interstates and c.) stopped to redline-RPMs in 1st gear. I've also looked around at the Dyno (where is the horsepower?) and tried to assimilate the info using a great read by InjuneerZZ here:
Scanner readings article .
In Summary: Through all that I'm stumped and though I have several friends that are mechanics and work on my car - this is also beyond their experience and understanding. If anyone who I'm not already talking with would like to review the logs/recordings I'd be happy to send them. I also have data exported to excel spreadsheets available. Basically in the area I live, my resources have been mostly exhausted. Mechanics/Shops in the area can't solve this or diagnose with accuracy. This ongoing issue has be very frustrating. Help is greatly appreciated. I really want to get this car where it should be performance-wise. To the store and back; great. Any significant distance and we have 'bog-city'.
'95 Firebird LT1 Runs Like Jekyll, Hyde
