I didn't know where to post this so I hope I'm in the right place. First off, I have a 85 Z28 w/LG69 engine, dynomax exhaust, MSD Distributor, Holley 600 carb w/e-choke, no ECM, no smog, replaced tranny w/ rebuilt 700r-4 w/b&m shift kit. My engine usually idles around 750(600 in gear). Lately, after I have driven around a little, my idle speed is about 4-500 in park! I lopes quite a bit and it seems to have lost some power. Fuel economy is also down. Any idea as to what could cause it?

 

my old 83 Z with an l69 did some what the same thing but it would stall out most the time if i let off the gas... any way i put 93 octane gas in it and it didnt stal any more and ran great i found out later my timeing was off... so if i were you get ahold of a timeing light and see if its off thats what id check first... also another thing to check that ive had happen also is a burnt plug wire or two wil make your car do that.

 

Yeah, it's possible your distributor has slipped and retarded the ignition timing if the retaining clamp that holds it in place wasn't firmly tightened down, making sure that both "arms" of the clamp are actually on the hold-down area, not slipped off to the side.