Idle RPMs Increases as Engine Warms Up

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ironwill11
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Idle RPMs Increases as Engine Warms Up

Post by ironwill11 »

Here's my issue- My engine idles steadily and starts reliably, however, the idle starts at 1500 rpm and increases to 1900 rpm as the coolant temp goes up.

I am not sure why this is happening or what could be causing the rpm increase. My msq & datalog is below.
2016-07-13_20.04.08.msq
2016-07-13_21.00.27_IDLE INCREASE.msl
Background:
4.3 TBI with MSII version 3.0
TunerstudioMS 3.0
GM HEI 8 pin module
DIYAutoTune 10' wire harness
IAC - GM IAC, 4 wire (square plug)
IAC is wired properly according to the diagram and markings on wires in harness (have verified correct wiring about 87 times now and pulled the IAC and watch it fully retract when key is turned to run). The only issue I see is that it fully retracts when the key is turned on and then goes back to its normal position without turning the key off.
I have read through all relating manuals several times, and researched other articles on the subject. Ready to go bald and pull out my hair. :shock:

Would appreciate any suggestions, insight, help- anything!- that might point me in the right direction.

Will
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Matt Cramer
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Re: Idle RPMs Increases as Engine Warms Up

Post by Matt Cramer »

Adjust the IAC position curve to close the IAC more as it warms up.
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ironwill11
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Re: Idle RPMs Increases as Engine Warms Up

Post by ironwill11 »

Thanks Matt,

Even at fully warm 160 degrees (as in TS) it is still idling high. I have it fully closed at 160 steps as the manual suggests.
Any suggestions

Will
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ironwill11
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Re: Idle RPMs Increases as Engine Warms Up

Post by ironwill11 »

Tried adjusted the IAC so it closes more. Seems to have no affect.
Also changed the accel enrich to trigger off of the MAP instead of the TPS encase that 5% fluctuation makes a difference. This did not seem to help either.

It still idles around 1500rpms. Tonight I shut it off and restarted so it was hot and then it would idle around 1150 rpm but the afr was reading 7.5. I datalogged tonight's test; however, it will not let me post it on here as it says it is too big at 1.7mb. It is pretty much the same as the last one anyway.

I have read through the manuals (yes all of them), everything I can find online.
Anyone have any suggestions at all???

Will
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Matt Cramer
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Re: Idle RPMs Increases as Engine Warms Up

Post by Matt Cramer »

Make sure you have the homing steps correctly set.
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kjones6039
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Re: Idle RPMs Increases as Engine Warms Up

Post by kjones6039 »

You might also try setting it to always on. My experience has been that moving only doesn't work very consistently.
Just a suggestion though.

Ken
1979 Corvette - 383 CID SBC w/ Holley Pro-Jection 900 CFM TBI, 4-85 lb lo-z injectors & Walbro 255 pump
MS2 v3 w/ms2extra 3.4.0 Release
36-1, Delphi LS2/7 coils in wasted spark, driven by v2.0 logic board from JBPerformance
Spartan Lambda Sensor from 14point7
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ironwill11
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Re: Idle RPMs Increases as Engine Warms Up

Post by ironwill11 »

Thanks for the replies. I actually did get it to work once. Found out that the distributor was loose and moved and the advance is holding my RPMs up. However, I have been adjusting the distributor (timing light broke - getting a new one). I can adjust it to the point it idles around 800rpm but any lower and it will not start. Also when it is cold at it will not start and stay running when the distributor was adjusted for that.

Question: the 4.3tbi only has timing marks for TDC and no advance as what GM does. Should I have mine set at TDC and have the advance manipulated solely with MS II?

Will
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Matt Cramer
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Re: Idle RPMs Increases as Engine Warms Up

Post by Matt Cramer »

ironwill11 wrote:
Question: the 4.3tbi only has timing marks for TDC and no advance as what GM does. Should I have mine set at TDC and have the advance manipulated solely with MS II?

Will
Yes. Best to have the ECU running timing.
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