I just replaced my throttle body with a 58MM BBK and I can't get my idle to drop down below 1100-1200 rpm. It seems like the air leak is from the lower front of the throttle body. If I put my finger over the hole the idle goes down and all seems good. Any ideas?

The engine is a 1989 L98 with speed density conversion, everything was fine before the change.

Is there a difference in throttle bodies between 85-88 and 89-91 other than the throttle linkage.

 

heave you adjusted the minimum air speed by jumping the aldl and adjusting the idle speed screw ?

 

Yes I have and have set TPS voltage with scan tool.

 

sounds like the iac is stuck if you commanded it in and set the min adjustment.

 

I just pulled off the bottom plate to make sure the iac was seating. With the jumper in place the iac is seated but when removed it backs out a little ways.

 

did you have the iac out when you swapped it over to the new throttle body ?

 

No, i left it in the bottom plate

 

Just curious, but is your throttle body new or used. I had a used holley that had a bad vacuum leak around the butter fly shaft, I had to buy a rebuild kit to fix the problem. Sometimes used is not so good, except for the price. Any ways, just a thought.

 

This was a unit that had been mounted but not used. So it was not new but not used . It cam in the original box with all gaskets and mounting bolts and looked brand new.

I put my jumper in and seated the IAC and unplugged it, started it up and it idled great. Since then I have plugged the IAC back in a seems to be good, I'm not real sure why it was backing out so much. After diving I notice that the return spring setup on this throttle body is very stiff and I have a manual, is there a way to lighten this up?

 

bbk's do have a tight return spring no way to weaken the tension on it.

 

Sorry to be the old thread resurrect-or but i'm having the same issue with the same part. Will do another iac reset. I have a scan tool that i use to put into service mode but maybe i'll try the jumper instead