Hi Matt

I was glad to see that you found an air leak coming out of the oil separator.
That should help the mileage a "teeny" bit as the ECU will have better information coming in.
The AMM was out of the loop (air amount off) and the signal from the O2 sensor was conflicting the program, of a set amount, when looking at the amount of air supposedly that was coming in through the AMM.

I'm thinking the ECU could trust the O2 sensor more since these things are suppose to watch emissions very closely. Rich and lean codes pop up all the time and very very often before anything else turns on the CEL's.
I would suggest putting a fast responding meter on the O2 sensor to verify that it is hovering in the mid range of 0.5 DC volts of the one volt range a majority of the time on a completely WARMED up engine. I agree they are expensive!

Make sure the thermostat is a 87C or above and working properly, if you seriously want better mileage! I recommend Walher as being the most sensitive and not opening prematurely.

Now I wonder, what is the deal with the ECU having a resistor issue, if the circuit in question, was only for a shift up indicator light? I gather these black boxes are tricky, if other circuits are powered off another.


As far as the over idle speed at start up, it should do that, all in one fell swoop if the IAC is working properly with the ECU. It could be stickingfron gunk or worn depending on its age in service.

Check to see that he throttle plate is not hanging open or set to high.
Check the cable for slack on the drum. Check for a completely closed throttle plate with the stop screw just up against the lever to STOP the lever not hold up anything.

Check its vacuum hose for gasoline residue wetness or smells.
I agree it can be an issue if you had wet plugs beforehand!
Put a piece of fresh hose on to rule that out in the interim. The rubber can absorb the vapors that can linger about in the manifold over time.

It appears that you are on the downhill side of fixing this thing!
Phil