[Gmecm] '7730 Stumbles at cruise

[Cowen]

Hello folks,

It has indeed been quiet, so here's a question to generate some discussion.

I've got a stock '730 ECM from a 3.1 running, a 3.4, with injection parts from a Fiero 2.8, with DIS.  This setup has been going almost flawlessly for about 2 1/2 years now, and I love the power, mileage, low emissions, and year-round easy starting compared to the carb it replaced.

Unfortunately, it has picked up two small issues in the last 6 months or so.  First, it stumbles a bit at very light cruise. I have no VSS yet, so I'm pulling a code for that, but nothing else.  I have the (digital) EGR vacuum plugged too, but I don't think it enables without VSS anyway.

Secondly, when the engine is cold, the there's a bog coming off idle unless it's revved up.  This feels like the IAC is closing in response to throttle input.  I had this problem when I first got things going, because the throttle plate was adjusted for a 2.8 and the IAC had to overcompensate for the air in a 3.4, so properly adjusting the throttle body completely cured it, until now.  I've tried increasing the throttle at idle slightly (reducing IAC counts required), but it hasn't affected the mild bog.

I know my setup isn't perfect with no VSS (I'll be transplanting the whole shebang again into an MGA next year anyway), but the thing is it didn't have this stumble for more than a year of operation.  I've done a quick check for loose connections at the TPS and IAC and they look good.  I can't find any vacuum leaks and it still runs wonderfully otherwise.  

Any suggestions on what I should focus on?

Thanks!


       
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