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Braindump regarding warm-idle issue

Forg

Well-known member
Joined
Sep 17, 2003
Location
Retirement Village, Sydney
Project Big Red Car has a MAP-sensed MoTeC M84 running Bosch -363 injectors, KG2T, LS1 coils (custom crank wheel plus dizzy-mount sensor), and a static CR that's probably too low for the KG2T. IAC valve is a MotorCraft unit off an EEC-IV mid 80's Falcon, these should be large enough to feed a B23E+T.

Given the lack of low-revs manifold pressure, it's running open loop.

Now I drove it to work this morning (first time in 6 months) and once it got warm it became apparent there's an idle issue. It sits on the target ~900rpm for maybe 20secs at a set of lights, then ramps down to about 500rpm where it's struggling to keep going. I didn't bring the dongle with me so haven't bunged a PC on it yet, so I'm kinda brain-dumping in order to start looking at it ... also looking for suggestions.

I guess the first place to start would be checking that it's getting a correct RPM reading (should be or it wouldn't work at driving revs), and then look at what it's trying to do for idle-air, fuel & spark at those revs/load? I don't recall there being a massive number of options regarding how it tries to do stuff, it seems odd that it can keep struggling along at 500rpm but not hold at a much smoother & easier-to-maintain 900rpm though, unless the IAC isn't big enough & maybe it's adjusting timing &/or fuel once it drops a reasonable amount below ~900? So maybe there are parameters on how it deals when it struggles - would that make sense?
[Yeah the manual is online on the MoTeC site if I can't get to the back of the garage to drag it out - will look later]
 
Was it working fine before?

What frequency and PWM open/close limits do you have the valve set to?

Been working with a few of these lately with MS and their native applications. They seem to work only in a narrow operating range. Being that the valve uses engine vacuum to assist operation, if the valve is installed backwards it'll also cause erratic behavior.
 
So, do you want help or just answer the parts of the questions not directly relevant to addressing the issue?
 
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