[Gmecm] Closed loop and stalls

[Michael Kaczmar]

I had this problem on an LT1 I did. Motor was modded with a Hot Cam,
lots of port work, and a 52 mm TB. Once we got the A/F issues figured
out (LS1 MAF installed with LT1 MAF values make the motor over fuel by
about 30%...) We still had a closed loop idle issue, which sounds very
similar to your issue. I also thought it was either the IAC or the TP
sensor. I watched the TP sensor with a DVM, and saw the value fluctuate
start at a voltage, go down, and then go back up again through the
first parts of the throttle opening. I also saw the IAC going nuts.
Turns out his T-body had a min throttle angle stop that was turned out
too far, and the throttle leakage area was too low. I opened that up,
more than I thought it would need, but I saw the TPS start to function
right, and the IAC settled down. I figure either the TPS was causing an
issue, or that the throttle blades needed a little more leak by at
idle, and the IAC had to max out/open too far to compensate. It did it
by gut reaction and by ear, but it seems the greater throttle leakage
let the IAC run within its window instead of maxing/min'ing it out. 

So:

1 - try cracking the throttle open a bit more than you have it. I do
not remember TPI's as well as I would like, but I think you can set the
min throttle a bit. Perhaps your motor pulls more air at idle than it
used to, and you may need to let it breathe some more. An old carb
tuners trick was to drill the throttle blade for a little more air, but
I would try to adjust the min throttle angle first to see if that
solves your problem. 

2- If you can, see if the TPS can be adjusted. Older ones could be
adjusted, but on LT1's it is non-adjustable, I assume the ECM learns
the limits. 

3 - Erratic idle can also be caused by a gummed up IAC. Pull it, check
the pintle, and make sure the seat is clean and in good shape. 

4- I know with a Tech-II you can reset the IAC sometimes the IAC
offests go too wide, and never get back to normal, if you adjust the
throttle reset the ECM to see if it learns in any different. 

HTH, all friendly and flame free. This should be a learning site, and
if anybody thinks somebody is acting like a d!ck, remember, it's hard
to read emotions in print, so somebody might have just phrased
something a little off, and not meant anything by it. I have been on
email digests for 10 years and see this all the time. Now, <group
hug>... ;-)



Michael Kaczmar
Creator 77/94/95/96 Caprice a.k.a. Frankenstein LT1/MN6
2004 Impulse Blue GTO, LS1/M12
53 F-100 5.0/T5, Mustang II, T-bird IRS.....
see http://www.geocities.com/abbynrml94 for project pics!!


		
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