[Gmecm] Re: [Diy_efi] 4.3L TBI Timing Issues.

[Cowen]

In case you've run out of ideas for your timing
issues, here's what came to mind:

I know you've identified the problem as timing, but I
had similar driveability problems when I put FI from a
2.8l onto a 3.4l.  I hadn't reset the idle adjustment
screw on the throttle, and there wasn't enough airflow
for the increase in displacement.  It ran fine because
the ECM opened the IAC a few stops to compensate, but
when you applied light throttle, the ECM counteracted
that by closing the IAC!  Result - it felt like it had
no torque off idle, stumbling a bit.  After setting
the idle stop properly, it idles with the IAC closed
and runs fine coming off idle.

Another idea: on Toyotas with EST, you can't set base
ignition timing unless the TPS is perfectly adjusted -
it thinks you're off idle and won't go into timing
mode.  Now I know we're talking apples and oranges
here, but from what I've read on this site, GM has
done a few counterintuitive things too... so is it
possible the TPS is adjustable on your model of
throttle body (some were)?  If so, is it reading
correctly at idle?  

Does it idle at the right idle speed (for
thatparticular BIN) +/- 50 RPM, or is the ECM
compensating with IAC?
Just some ideas from someone who's learning too!  Good luck.

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