It threw a code too (I think 43?) saying there was an IAC issue. I swapped in another IAC I had from another TBI I have for parts. Didn't help at all! I am thinking the IAC is fluctuating like it is trying to account for the vacuum change resulting from possible leak(s?). It seems like maybe there may be a vac leak from under my TBI. It is a 50mm bored unit so there isn't much aluminum on the gasket (TBI body got pretty darn thin from the boring). Also, I tried the carb cleaner trick for testing for leaks and it DID smooth the idle surge a bit, but this method has been inaccurate for me in the past so I am not sure what to do at this point. Should I rip the intake back off and replace my intake manifold and TBI gaskets? I just want to make sure I am barking up the right tree before I tear in...Again!

BUMP! C'mon guys! No ideas!? Ok, then new question...How can I tell if my intake does indeed have a vac leak (btw intake and head)?

Whats your datalogger telling you? Is your IAC zero'ed out but your idle is still fluctuating? Usually a bad IAC will cause a rpm "hang", quick idle surging is usually the result of a bad fuel mix or timing problem. The IAC actually moves rather slow and will cause a slow rolling rpm change.

What is the rest of your combo? What bin file did you start with? These kinds of things help us help you.

Unfortunately I didn't even burn may own chip- TBI Chips did. I have a 96 vortec 350 block and heads with a summit carb intake (no egr) and a holley adapter plate mounting my 50mm xtreme efi TBI unit. I have 55lb injectors running at 18psi. I have an LT1 stock cam and roller tip rockers. I think thats about it...? And YES, it is a fast surge, not really slow and rolling.

Well I just called Brian and it looks like I will need to get some datalogging equipment anyways. This is definitely uncharted territory for me! I have no clue how to proceed. I've read through the DIY sections on here and always come away completely lost! I have the 8192 baud computer because my truck is a 94 so that rules out the "cop car" mask right? Otherwise, I guess my engine is kind of close to what the cop car would have been.

You just need a 350 bin to start with, you'll be changing just about every parameter by the time you are done tuning.

You most likely have the PCM that is so popular on these boards. The PCM is so much more advanced then the older TBI ecm's that most of us are running. Get your ecm number and do some searching on here and see what comes up. Go ahead and read the "free tune" thread as a lot will still pertain to your ECM, the basic tuning theory discussed will help you make sense of it all.

If you choose to go with the log and mail routine with Brian be prepared to spend a LOT of time getting it even in the ball park. Even if you get it drivable you'll be leaving a lot on the table.

whats your idle 600rpm base (bypass) inital timing at? 10°BTDC?
did you use the felpro 1255 intake manifold gasket or th compostite
style gaskets?

airdeano

You've probably got the throttle blades open too far and the IAC is all the way shut and the PCM is resorting to pulling timing to keep the idle within range. Mine did the same thing.

Ok guys. I think I found a first step to take. I had to change out the throttle shaft because my linkage was different than the stuff that came on the TBI. I used a dremel and widened the throttle blade mounting surface. I called Vic Morse from Morse Machining (a company that bores TBIs) and he said it sounded like the plates might be binding up a bit from my dremel work. Looks like I need to swap the old shaft back in and see if it improves anything. I know for a fact the tune is way off too. The thing wreaks of richness. I ordered my ALDL cable last night. I'll be doing some datalogging when I get a chance.
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As for gaskets...They are Victor Reinz and are plastic with the rubber/silicone surrounding the ports. IDK base timing yet. I set it as close to zero degrees as I could with the shitty vortec timing cover (no #s just a slotted mark at zero)