1990 GXL automatic, NA, 76000 mi., wont idle, replaced BAC, ohmed BAC-ok, 6 volts @ BAC connector w/10kohm resister - ok, TPS's ohm good, set for one light, engine drops 200 rpm w/brakes, drops 200 w/steering, drops 500 w/AC, drops 700 in drive. Will idle @ 1000 smooth, rev it and it comes back to 1400 and surges @ 1000 to 1400, but sometimes it goes back to 1000, sometimes it just slows and dies? Also when duct from ThrotBody to AirFilt is removed engine starts, goes up to 1000 rpm then dies. Will not run w/duct removed - this seems very peculiar to me? Any help appreciated. Thanks

 

Dies with air duct removed because your removing the air flow meter from the mix—your just allowing unmetered air into the engine.

The idle dying with accessories on could be a dead transistor in the ECU. See https://www.rx7club.com/forum/showth...hlight=bac+fix

 

Checked output to BAC w/10k resistor, its putting out 6.1 volts AC. Hooked old BAC to connector and the solenoid is vibrating back and forth. The adusting screw on the old BAC appeared to be locked with a blue sealer, I broke it free to look inside, theres a metering needle. I have the feeling these are factory set and really shouldnt be adjusted. Anything else I can check. What does the screw at the back of the ThrotBody do, its under a red cap. Appears to affect idle, I turned it back to where it was.

 

Nothing wrong with adjusting that air bypass screw in the bac (if we're talking the same screw, its recessed in a tower). There's minimal adjustment that can be done with it. IF I remember right, from all the way in, if you screw out a full three turns, thats about as much as you can get out of it. You can turn a lot more out but it does not help. After three turns approx the bypass hole is full open. Blow into your old one while turning the screw and you'll see.

How about this. Put your meter on the bac wire that goes to the ECU (the one thats not black/white) and see what the voltage is at idle with all things off except the engine. I believe you'll see approx nine volts. Now turn the a/c on. How big a voltage drop did you get??????

Do you know of the FREE download of the factory service manual at http://www.fc3s.org ?????? Download the Fuel section for the 89 model. Close enough.

Is there anything strange about your engine that we should know about??? Street port? 87 throttle body on a 90??? You know, anything not stock??

 

I put the red teminal of ohm meter on green wire (not white/black) and black terminal to ground, got senseless # checking AC or DC volts, Tried connecting to both wires on terminal, same nonsense. Put the 10k ohm resister back in - 6.2 v AC with Air Cond off, 7.2 v AC with Air Cond on. Everything on car is stock except new BAC, plugs, and air filter. Car is for daughters birthday today. Needless to say its not going well. Thanks

 

Re-adjusted TPS as per Hailers, sits about 0.98 volts at 900 rpm. Some more info - Major problem is I have to hold down gas pedal for 2300 rpm to drop into Drive and hold 900 rpm without stalling. Help.

 

Oh. I see a important figure. That 900rpm. There's a thing about the bac. If idling above 750 you'll hardly notice anything if the bac plug is taken off. From what I read on your pm, I'd say your bac circuit is ok to some degree. When you were talking about the rpm dropping 200 when steering , 500 when a/c is on......is that from 900 rpm??

Be careful and don't short the bac wires while working with it. Attached is jpg of a relationship chart out of the 89 manual thats online. I've gotta go weld some rack in the garage. I'm running out of weekend fast.

And on the tps. Thats just fine. It can vary from 0.9 to 1.05 and the car will never show any difference. Beware that as the car cools off , as in the morning, the tps will change in output but will come back to your setting as the engine fully warms up. You probably know that but I thought I'd just throw that in

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