'7427 IAC problems

I've got a '7427 system that is running on a IH345 - I've got good fuel and timing adjustments. I've been through 3 PCMs (All '7427 $0D) now and I still can't figure out my high idle/oscillating problem.

The best I can tell I have a wandering IAC. From a cold start it works reasonably well. If you stop then start the engine and it will high idle. I'm assuming the cause is the IAC being too open and more fuel being called for to richen it. The TPS is around 0.55v (+/- .01v), but the TP Dash throttle reads about 10%. I've set the target idle speed to all engine temperatures to 650. So it should never reach over 700. But it'll idle 1100-1400! I have the manual flag set.

Without a P/N switch, how does someone adjust the throttle plate? I've never got the shorting of the pin trick to close the IAC to work.

This is creating a safety issue since I have an auto trans (727) I have to brake harder to overcome the added power to the torque converter.

TPS volts sounds right, but % should read 0. The '7427 has a section of code to automatically set the 0% throttle position. What counts do you show for IAC? Make a datalog recording of what it is doing so we can look at ALL the info.

Yeah if you can get a short log of this along with the bin file we could probably find the issue. Something is wrong if your showing 10% TPS after a restart? Maybe your adx file? It should reset to 0% at restart each time. May as well post the data log, bin and adx file.

I forget what I did with the kids 16197427 345 IH to get IAC closed? Your right the crossing of A and B does not work like on 1227747. Maybe someone knows correct procedure for 16197427, if not his truck will be in shop Wednesday and I will figure it out again and document it. But we did get throttle blades/min air set and have about 21 IAC count when warm.

We are running $0E in a 16197427 and manual trans, in $0E there is an idle table and an adder idle table so this may be why your not getting your target idle. Oscilating is usually a vacuum leak but from what your saying this does not happen first cold start, just after restart? Idle will go higher on restart from another table but should settle down after a bit.

So it's an auto trans, no P/N switch, checked for manual trans... do you have a VSS? Any error codes?

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Originally Posted by EagleMark

I forget what I did with the kids 16197427 345 IH to get IAC closed? Your right the crossing of A and B does not work like on 1227747. Maybe someone knows correct procedure for 16197427, if not his truck will be in shop Wednesday and I will figure it out again and document it. But we did get throttle blades/min air set and have about 21 IAC count when warm.

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When I swapped in my mpfi, I needed to set the min idle, as my idle iac counts were crazy high, I needed to open the throttle some. What I did was plug in a spare tps thats not attached to the tb, then started the engine, let it come to idle, then watched on my laptop screen and started slowly adjusting the throttle stop, the iac counts slowly started dropping untill I got it to a reasonable level. I shut it off, slotted the tps holes, then re set it to where it needed to go, and all is well.

I've managed to get something to work, but it's loud... If you pull the IAC out with the engine running, the PCM will tell it to extend (slowly) until the pintle extends enough, then unplug it and screw it in, you'll be able to shut off the IAC port, then set the idle. However, I do not know what/if/how the PCM has the correct numeric value. I figure it would drive it closed, then reset the value on every start. But I don't think that is happening.