BAC Valve idle adjust? + PICS
 

On my 88 Turbo, there is no screw for adjusting idle.

Could someone please show me a pic pointing to this seemingly absent screw? I'll go outside and take a pic of mine in a minute.

Also, another small problem: Car idles ok, at around 750-800rpm, but when i rev it, it catches at around 1200rpm, and idles there.. It doesn't return to 750.

Does the idle adjustment screw near the dashpot set start-up idle, while the BAC idle adjust screw set's driving idle (so to speak)?

Or am I way off :wallbash:

Thanks, Bryan

http://img90.imageshack.us/img90/729...0164lb6qw7.jpg

http://img90.imageshack.us/img90/240...0165te8df4.jpg

Where you trying to find the idle adjust screw on the BAC valve itself?

Yes? Are you saying its not on there?

ok....the bac adjust screw does not adjust idle. the idle adjust screw is located on the back of the throttle body towards the firewall. the BAC adjustment is for fine tuning the idle if you have AC and or power steering IIRC...

EDIT: I just looked at the pics again and realized that the BAC you have isn't the same as the USDM Bacs. The one you have, I believe, is the same as the Jspec BAC which has no adjustment screw.

So as far as your 1200 rpm idle is concerned, i'd remove and clean the injectors or check for a vaccum leak.

Oh ok, thanks for the reply.

Why do you say injectors? Because they could possibly be staying open after i release the throttle?

No Vac leaks that i can find, and BAC valve has been cleaned. TPS has been set.

Could be that they're clogging a bit.

I'd also check the vaccum line going to your fuel pressure regulator just on principle...you never know...

My car does(did) that alot, I think it had to do with the thermowax, we'll see if it was that when it is running again.

Your throttle body might just be getting stuck. See if your butterflys are dirty?.

First, the idle should be set @ 750 with the throttle screw, with the set coupler grounded, so as all electronic info is subdued. The ASpec BAC has an idle adjustment screw to fine tune the idle to allow more air to enter the manifold. You have a JSpec BAC that has no adjustment, so the idle should be set via throttle screw on the UIM. After the idle is set, check the TPS with a digital ohm meter to be certain it's functioning properly, then set it acording to the FSM, with the final adjustment with the light checker, but you can use the meter inplace of the service light. Check the function of the BAC by disconnecting the electrical connection, and or by applying 12 volts, but be careful as you don't want to short out the unit. Check the inner seal to be certain it's not leaking air, but from what you have stated, it seems as though the BAC is not causing the problem.


http://rx7.subbuteoclub.com/idlecontrol.shtml

First thing that should be checked mechanically is to see if the throttle lever is actually coming in contact with the idle speed screw. If it is being held away from the screw, either the dashpot is out of adjustment or binding or the thermowax unit is still engaged. Also check to see if the engine is reaching normal operating temp, if it is not (due to a weak or missing thermostat) the thermowax unit will not move off the fast idle position.

slightly off topic, but I didnt think it was worth a thread of its own.. are the BAC's from an S4 TII and an S4 NA the same?

im going to bring this back, since I have an S5 N/A and my idle is the same way, it will idle normal, tap the throttle it will bump to 1200 and stay there. If I start to turn on an electrical load ie: headlights and heat, it will pull the idle back down.

Adjust your TPS...that may help.

no the bac's on TII is diffrent than the one on a series 4 n/a. if ya put two side by side the hose possition for air intake is diffrent

mine does/did that high idle at normal operating temps. Usually if i just tap the gas it will sink back down to 750 rpm. I havent gotten a chance to pull open my throttle body and look at the butterflys but I wouldnt be suprised if that could be the problem. It kinda just makes sence in my mind that taping the gas may un-stick the butterflys if they are stuck.

its in spec... it seems to me like once the car is under a load, it isn't bumping it self back up.

Yeah same here, when I tap the brakes my guages actually flicker for a split sec. I was messing with a few BAC's today, I guess I have a Jspec one also, it doesn't have the adjustment screw, I think I saw a small screw in the whole though. I put a USDM one in and it started idling at 3 grand and never came back down. I tried adjusting it with the screw and it made no difference. The line for the vacuum hose wasn't angled up like the J spec one though, I guess it was a turbo one. I could've sworn I read somewhere that you could just route the hose differently and it would work. I just cleaned my old one with parts cleaner and set the idle with the screw on top of the TB with the rubber piece on it to a nice 800 rpm.

I also get the dash light flicker when tapping the brakes...so did cleaning the BAC out help?

The TPS can be "within spec" and still need adjustment. Or are you saying its adjusted properly?

Also, my BAC valve doesn't have the adjustment screw. S5 NA. In fact, all three of my S5 NA's don't/didn't have the screw. I was under the impression that S5's in general didn't have an adjustable BAC valve - where S4's did.

not really, idle smoothed out a bit I think but thats about it

Once again, have you checked to see if the throttle lever that touches the idle speed screw is actually touching it when your idle is high? If it isn't, then your thermowax unit may be holding it at fast idle. Your dashpot (if you haven't removed it) is designed to allow the throttle to close gradually to keep the engine from stalling when you take your foot off the gas. If it's binding it could be causing your intermittent high idle. Try removing it temporarily and see if that helps. Also, if the BAC is causing an occasional high idle, use a pair of needle nose pliers and pinch together the hose that goes from it to the air intake duct with the engine idling. If it returns to a normal idle (or even lower) then it could be the BAC. If not, it's elsewhere. Another thing to try if you have the factory BOV (bypass valve) is to pinch it's hoses off when you have a fast idle. If it comes down to a normal speed, it may be sticking open. The FSM has lots of useful info on all of this. It would be more helpful to know if your idle lever is against the screw, so report back on that.

1989-1991 FSM Under Fuel and Emissions Control Systems, Non-Turbo

Pages F1-15, F1-16

The FSM can be found on the FAQ for 2nd gen sticky on the top of this section.

yeah I have the same exact problem. Used to have a JDM Tii BAC now I have a Aspec BAC, the problem was not fixed. Sometimes, it randomly goes to its normal idle, but then as soon as you hit the gas it stays arround 1,4k rpm.

I’m dealing with a low idle and someone suggested it’s the BAC. I have a S5 NA. I tried swapping to another BAC(in hindsight the current one was still good) and got no change. Using the idle adjust screw, I am unable to bring it up to 750 as it stays at 400. Car is “drivable” but not happy. Any help is appreciated:)