Is this cause for a rougher than normal idle? The car (92Z LB9, stock w/ K&N's and Edelbrock cat-back) started this when the alternator was on its way out, and replacing that didn't cure this. It also was slightly surging on the highway, but that seems to have corrected itself.

Just got datalogging, so not sure if it was at this level before. From what I have read online, this reading should be under 35. Higher is closer to atmosphere, so maybe I have a vacuum leak? I have looked and listened under the hood but haven't found anything.

Thanks,
Jeff

 

A vaccum leak will show its ugly head under conditions of high vaccum(i.e. low kPA). Cruise and idle will suffer with a vac. leak, so it sounds like a good chance you have one.

 

Yeah, I must have one, but damned if I can find it. Did some more looking today, including soapy water and propane but nothing showed up.

Now it is running so rich (O2 mv's in the 800's) it can barely idle or cruise, and the surge is back. Wierd because it had been fine for 2 days...

 

Its possible when you changed the alternator you put a hole in the plastic/rubber line leading from the throttle body, under the alternator, to the charcoal canister.

 

I should clarify, the symptoms first started when the alternator failed, not when I replaced it. Using DataMaster, it tracks up as high as the 50's at idle. I'm pretty sure this is part of my high HC problem because the fuel trim is in cell 4 instead of cell 1 at idle.

I'm also chasing a ridiculously rich condition (O2 above 800mv) that I can't put my finger on. I drove the car two days and it was fine, now its back to driving like garbage and will barely idle. I just changed the plugs again, and the air filter, fuel filter, wires, cap, rotor, and O2 sensor are only 8,000 miles (and 2 yrs) old. I'm stumped!