New to TBI, HELP! High idle problem has me pulling my hair out

[Mrcar1955]

These forums have been very helpful so far, so I thought I'd post a question in hopes that someone might have a good tip.
1989 R2500 Suburban, 7.4l TBI purchased a couple weeks ago.

-no check engine light on and it seems to be working
-had a high idle when purchased
-should have checked these forums earlier, but replaced the. Coolant temp sensor, IAC, and the vacuum lines- problems continued
-the forums led me to check for base gasket vacuum leak and, sure enough, found a good sized leak at the base gasket.
-pulled TBI off and rebuilt it using a rebuild kit from Napa.
- re-installed the unit with hopes that I had solved all the issues - no luck

Now:
- high idle remains (1000 rpm)
- very LOUD squeal coming from throttle body that only goes away when throttle is beyond 1/2 open. Hard to tell, but may be leaking air around the shaft of the throttle body. Idle lowers when I spray around the shaft area and throttle return spring.
- I checked the shaft for slop when it was off the truck and it didn't seem sloppy enough to let that much air through.
- oh, I did ensure the IAC seat was clean and I had it fully extended then disconnected it when conducting all the idle checks. I thought that it should barely run with the IAC port blocked. So, where is that much air coming from?

I'd like to stick with the TBI instead of throwing a carb on it.

Any other thoughts before I spend big bucks on an entire reman unit?

Any one done business with throttlebodyinjection.com? They sell a reman unit for about $350 which may be my next stop.

Sorry for the long post, but this thing is driving me nuts! Thanks in advance for the help

 

[Georgeb]

You might double check that the gasket is ok around there.

 

[Mrcar1955]

Yep, I've had it off three times now. Gasket is flat and both surfaces are clean.

 

[Georgeb]

Perhaps somthing here will help
http://www.gmsquarebody.com/forum/showthread.php?t=13089

 

[rich weyand]

You still have a vacuum leak, such as from a bad vac can or brake booster. So, lots of air getting in and the TBI is adding fuel to make the mixture come out right.

Remove all the vacuum lines and cap off the ports and see what you have. If that solves it, add them back one at a time, and fix whatever makes the problem return.