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IAC and SEPST

5K views 19 replies 9 participants last post by  Louis 
#1 ·
Bike shows all the signs of a dirty IAC. Stalls when hot. If it doesn't quite stall, after a bit the idle picks up and goes back to normal. I really want to finish some other stuff first before I take it off to clean / replace it. In the meantime I just saw a reference to an IAC setting in a tuner (TMAX as it happens - don't have one, don't want one). This stuff started when I switched from my PCIII to a SEPST. Are there any settings in the SEPST map that affect the IAC other than idle speed and fuel?

I'd guess not, but just checking.
 
#2 ·
Before you do that, replace your "System Relay". It's much easier and cheaper (especially if you break the fragile IAC screws that are bonded with Loctite).

Mine was doing the same thing, I thought the same thing. I removed, cleaned, and replaced my IAC with no joy (thank God that I did not break the screws).

I eventually replaced the System Relay to fix it.
 
#13 ·
My '05 B is having those issues,erratic idle..stalls sometimes..cleaned the IAC,and DID break a screw but was able to drill it out and retap with no problems..so System Relay? is there one on a 05?
 
#3 ·
Hmm. Yes, I had better blitz the electrics.

Still leaves the same question though - I have unwisely used someone else's map as a base. Could they have done anything to mess up the idle other than change the fuel loading or desired idle speed?

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#4 ·
It there a IAC initial calibration after uploading a map needed while using SEPST?
(Ignition on, run-switch 5s on, 5s off, 5s on, 5s off, ignition off)
 
#6 ·
I have, and use, the Daytona Twinscan.

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#7 ·
IAC initial calibration? Not heard of it. I can try that..

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#10 ·
Just do as karzza said (Ignition on, run-switch 5s on, 5s off, 5s on, 5s off, ignition off)
before you start engine. cycle switch and look down tb and see if you can see iac go in and out. I have sprayed with carb cleaner from top. Not sure it ever did anything but thought it could not hurt if it was dirty. maybe more fuel at low rpm? I'll try to look I think there is something to adjust just can not remember what. what is tps at idle?
 
#11 ·
OK, it's easy enough! I'll do it! But I'd love to know where it is in the bloody manual, because if I have missed this rather vital sounding step, what heck else have I missed?!

Will do it tomorrow and report back.
 
#18 ·
I have calibrated IAC for production so this is not a guess.
Most IAC motors WEAR OUT. They get sloppy and add or loose counts when running. As your problem happens both cold and warm It indeed could be calibration. First Idle position (TPS) must be within a range for proper IAC function. Anything done that changes TPS ZERO will effect IAC!
Secondly, those "warm up" stes are not intuitive on HOW they work! You are not "adding" any step in that TABLE. What that table does is modify the "IAC base learned position" vs. warm up steps.
A simply explaination is say at a given warm up temperature the "expected ERPM" is 1400. At "IDLE" the expected RPM is say 1100. The base learned IAC value at 1100 fully warm idle is ~15 counts.( for arguement sake) So if the IAC position at 1400 rpm vs. temp. and at that "warm up" point the IAC is at 26 counts, the "value in WARM UP counts" would be 11. If for instance you had only 5 counts in the warm up table at that point, the BASE LEARNED IAC posistion would go UP to 21 counts.
So if you rode down the road from a given temp/warm up table ERPM, when returning to IDLE the "fully learned Base IAC (Base IAC position is learned and changes slightly ever time). But in the above "senerio" your idle would hang high as the base IAC counts learn back to what is needed for 1100 rpm! However, IF you have too many "warm IAC" counts in THAT table, say 26 counts, where the actual counts are also 26, the base learned IAC counts would be moved to ZERO, so if you ride off and warm the temp. to normal, when you return to IDLE the "BASE LEARNED position" would need to LEARN UP form ZERO.

Warm up table values are SUBTRACTED from "current IAC" posistion vs Desired RPM(at a given temp)
Base learned IAC -warm up counts=current IAC base learn.

Those counts (warm up table) are there to help NOT change the "Normal" IAC base learn. So if your fully warmed up RPM needs 15 counts, you add the OFFSET (the number of counts for each increase in RPM vs TEMP) and then at whatever Desired RPM is when you ride off, and return to IDLE at FULLY warm desired IDLE the counts will be close and not droops or sags.
Many folks think they are "ADDING" counts in the warm up IAC table, but what that table does is a subtraction from "current warm up RPM vs temp." from BASE LEARNED position!!

So yes, that too can screw up fully warm IAC position if you had too many counts in the table and also IF that table is NOT ZERO at normal IAC fully warm desired speed!!

All that said, when you turn the key on/off/on/off,
all you are doing is resetting the IAC position!

The IAC does not have a sensor for POSITION! It ONLY "knows" where it is at key off/on reset. There is a table that drives the IAC into the seat then BACKS it OUT a calibratied amount of counts.
"Park Position" When you start up, the IAC motor assumes those "park position" counts as BASE position. As you ride down the road the IAC motor continually moves in and out vs. throttle! as well as desired RPM! As "slop" develops over time in the nylon threads of the IAC motor, the pintle can and does loose track of position as a function of counts.
So when you return to IDLE the actual pintle position can be very different than what the ECM thinks is IAC position..IAC motors are a large reason cars have gone to Drive by wire!
As you maybe can tell! I hate IAC motors as they caused me no end of trouble in my career!

It was always the calibration engineers fault when
 
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