P0300 Chevrolet -and two other coders--how do I find the exact problems?

Question

1997 3.8 liter shows 3 codes p0300, p1870, p 0420 engine idels a bit rough and mileage seems poor. Otherwise no problems, accellerates well. Check Engine soon light on. Chevy wants $250 to begin to isolate exact problems. 132,000 miles on it

Answer 1

P0300 Random misfire

P1870 Transmission componenet slipping

P0420 Catalytic below efficiency

With P0300 random misfire and P0420  Catalytic below threshold, you have a lean misfire, this can be from false air such as a vacuum leak that will cause this misfre to a EGR that is slightly stuck open, to the intake manifold. As for P1870 transmission component slipping, the TCC (torque convertor clutch circuit) may be the problem that if you experience the slip at 45-55 mph.

Comments

Thank you---how do I find a vacuum leak? Is the EGR easy to check or replace? ALso, I dont experience any tran slippage. Fluid isnt low---I read 1997 trans can have a problem w some valve? COuld it be that or just something simple? I dont want to have to have the trans rebuilt.Thanks!