I've fought with this for awhile with the help of Aaron over in the newbie forum. The car has a large Pineapple Racing! Street port. Stock turbo, stock intercooler, Apexi blow off valve, a hard pipe for the TID, FCD, Walboro 255, stock injectors, all emissions removed, OMP deleted with the oil injectors deleted as well, 3" racing beat turbo back to racing beat y pipe and mufflers. TPS is set to 1v at operating temp, the cold start system for the thermowax is adjusted properly.

As of now, there are no vacuum leaks. At temps of 70*F indoor start the car and let it idle and the idle with be about 750-800rpms with afrs between 12.5-11.4. I physically can not get the idle any higher with the BAC screw. I have completely removed the BAC and decarb it, checked and made sure that the BAC activated by applying 12v to it.

Outside in temps around 35*-45*F or colder the idle will hang around 11-1300rpms once warm and coming to a stop at a stop light. AFRs will be in the mid 11s, however, if sitting at a stop light long enough the idle will drop to where its supposed to be, but then the afrs are in the 10s. Letting the car slow down in gear at about 1500rpms you hear what sounds like an air valve activating and struggling, if you let the car drop below 1k RPMs doing this the idle will be at 800rpms but in the 10s for AFRs.

My question, what will cause this? I need to go standalone anyways, but would love to fix this issue now before going to that point and compounding a problem. If its caused by a sensor I need to delete when I go stand alone anyways, hey, that will suite me just fine.

 

Maybe you have a problem with the harness wiring going to the BAC. BUT... if it's idling steady at 750-800rpm, the BAC really isn't needed.

As far as cold weather driving and the idle being a little high, is the car up to max operating temps? If so, it could just be a slightly sticky throttle. AFR's in the 10's is rich for a normal idle though.

But here's the thing... You could still have a vacuum leak.

I had a HUGE leak on the back of my LIM. But I never noticed because my car always had good vacuum at idle and driving, drove well, made power, started well...

I only discovered it because the entire time my boost level was always dropping off at higher rpms. It should have held 10psi no problem, but was always less than 5 at redline. I sort of just accepted this. I wound up looking at something else and noticing a giant nipple with no hose/cap on it. Voila!

How the car pulled 17" vacuum at 900 or so idle and drove normally with a huge vacuum leak I have no idea. But it did!

So... you never know!

I say pressure/vacuum check your entire intake system.

 

I haven't pressure tested it since I went through it this morning/today and smoked it and installed the oil injector block offs. The car is is quiet as a lamb under the hood so there is no evident vacuum leak. (Well as quiet as a street ported motor can be). I've found little vacuum leaks easily enough at work by listening and spraying carb cleaner. I'll pressure check it next week at work.

As for the throttle, I cleaned all the plates last week and checked them again today, also checked the return, throttle returns quick and snappy. No sign of any drag at all.


As for the BAC, the connector had broken on the harness side and I replaced it with a new connector and matched the wiring correctly to where it was on the factory harness. Though it still doesn't mean that the ECU isn't trying to command the BAC


Thanks for the input.

 

One more thing...
The stock ECU 25 years ago was good for one thing... a stock engine. You start pulling things off, street porting(!), free flowing exhaust, ice-man intake whatever... something will go wrong. It may be subtle, but things will start having a mind of their own.

This is what we get. This car really is gimmicky and we're lucky we got it in the first place.

 

Yah, that and diagnostics on the stock ecu are next to nothing lol. Makes me glad I am a tech in the modern age, those older guys hate the new cars and I have issues with the older ones. I know I need to go on to stand alone, just making sure all the issues from the previous owner are taken care of before I advance on to the next part.