I have an 83 trans am with the crossfire TBI 305. Can anyone please explain how this works? How do they work at cold start. My rear tb is open at cold start while my front tb won't move from being closed. My car won't start and I was thinking that this could be why. Any information is greatly appreciated.

 

Q: My rear tb is open at cold start while my front tb won't move from being closed.

I will asume you are refering to the IAC's and not the buterflies. Sounds like one of the IAC's is defective. But my car always started on one of two open just idled lower RPM when cold on coolant. You could try cleaning it but odds are it is shot.

 

If you mean the IACs they are wired in parallel and should both be in the same position at all times.

 

You can cycle the IAC's with engine off to check their operation while looking down the TB. Dont know offhand which ALDL terminal to jump to ground. A search should find it.

I believe it is A and B. The two that are upper far right

 

My front butterfly is closed while my rear is about half way open. Where can I see if I have a faulty IAC?

 

OK. something very wrong. I cant imagine being that far out. Way out of adjustment or linkage defective. IAC is not your problem. The IAC attaches to TB unitand is a "stepper" motor. It retracts a pindle to allow a controlled VAC leak allowing a change in RPM. you can see it by looking down the bore into an area that is cast into TB unit. Appears black and is tapered as a cone like "pindle".

 

Yes, putting it in field service mode will cycle the IACs

But you mean the throttle blades themselves, what happened is someone messed with the synchro screw. It's the screw on the center linkage, OEM it has a collar over it that is brazed to prevent tampering. The brazing must have been broken, maybe the entire collar is missing.

The synchro screw works by moving one blade in respect to the other by lengthening/shortening the center link. How you do it is all relative, what matters is one blade's idle stop screw (on back of TB behind a little plug if not tampered with yet) and the other is adjusted off that.

Do a search on synchronizing CFI TBs. You'll need to build a small water manometer or do it with a feeler gauge (manometer = better). Too much to quickly type down here.

What you can do is turn the screw so that both TBs are open by about the same amount, at leas it should be sort of drivable as it is now the fuel delivery across the cyls is all out of whack.

 

Okay, changed the plugs and the car is running. It seems like it is idling really high though. Could that be because of the cold start or something else. Reads to be idle at about the 20 mark and seems to idle higher as it continues to run. Man what is up with this?

 

check vacuum leak?