IAC tuning. Am I crazy? (Solved!)

Ballistic · Post by **Ballistic** » Sun Jun 04, 2006 12:19 pm

grippo wrote: I looked at the data log, msq and don't see anything fishy. It does seem the idle should be the same if the steps are the same. The only thing I see is that the IACStart steps is 355 but in the table the steps only go up to 290 at the highest temperature. The way this is meant to operate is that the last entry in the table should be the same as the IACStart value and the pintle should be fully closed. By making the max value a little larger than it needs to be you make up for any missed steps and can guarantee the pintle is fully closed. Then the idle is set by cracking the throttle plate.

I arrived at the 355 number by manually over extending the pintle and then pushing the IAC into the throttle body so that the pintle is bottomed out when the IAC mounting flange is tight to the housing. I then would turn the key on and then check if the pintle had fully retracted or not. I thus determined that a start value of 355 was required to fully retract the pintle when it had been fully extended.

If you set the last table entry to 355 instead of 290 will you get a repeatable idle from cold and hot restarts ?

MT does not allow a setting larger than 300.

Also, I assume you have jumpered the large 1 Ohm resistors on the bottom of the board ?

Yes.

As far as why the steps do not prove repeatable - I'm not sure at this point. We have verfied that the new software puts out proper steps on a scope, and it is showing the correct commanded steps in the data log. The only other thing I can think that might be a problem is the step velocity (step time). This definitely has an effect on motors which I have seen many times in work. I believe you tried 2.5 to 4.0 ms steps. Did it make any difference ? If not, did you try 1.5 ms ?

I set up a dial indicator on the pintle tip, and with a start value of 300 steps, I got a retraction of 0.295" +/- 0.003" varying the step time from 1.5 to 7.5 ms. Step time doesn't seem to make any difference.

At this point I'm reverting to the 2.35x2 code as that seemed to come the closest to working. As is, 2.36 causes an engine stall on warmup.

Post by **grippo** » Wed Jun 07, 2006 8:18 am

You have verified the motor + software works well under retraction. If you repeated one of your tests and then drove the motor forward with a simulated warmup you should arrive at 290 steps, which should give about .241 in ((290/355)*.295).

An easier thing to try is to up the limit for the table data in your .ini file. Then you will be able to change the table value from 290 to 355 and see if that helps. This is done by finding the variable in the ini file and there you will see numbers that specify the scaling of the variable and the upper and lower limits. Just change the 300 to 400. If you don't know how to do this let me know and I will give you more details.

Meanwhile I will keep looking.

Another question - On the restart, if you let it run another few minutes does the idle eventually go down ?

Ballistic · Post by **Ballistic** » Wed Jun 07, 2006 1:31 pm

grippo wrote:You have verified the motor + software works well under retraction. If you repeated one of your tests and then drove the motor forward with a simulated warmup you should arrive at 290 steps, which should give about .241 in ((290/355)*.295).

I'll do more investigation as I'm able.

An easier thing to try is to up the limit for the table data in your .ini file. Then you will be able to change the table value from 290 to 355 and see if that helps. This is done by finding the variable in the ini file and there you will see numbers that specify the scaling of the variable and the upper and lower limits. Just change the 300 to 400. If you don't know how to do this let me know and I will give you more details.

Shouldn't be a problem.

Meanwhile I will keep looking.

Another question - On the restart, if you let it run another few minutes does the idle eventually go down ?

No, the idle is completely stable.

The hot restart behaviour didn't change between code versions. That is to say, it is consistant and OK.

I have an extra IAC motor. I'm thinking that perhaps I can put it in place as a dummy to hold a relatively consistant idle and then monitor IAC behaviour with the original IAC removed from the TB but hooked up.

Philip Lochner · Post by **Philip Lochner** » Thu Jun 08, 2006 3:40 am

[quote="Philip Lochner"] Tried 2.36 this morning. Seemed to work well. Certainly did not have the IAC "stuck" on wide open on the first start and did not have to restart. /quote]

Afraid I have to contradict my earlier report. On several cold starts (certainly not all cold starts) since that report IAC stuck wide open. Last night it only started closing properly (I don't seem to have the WUE issues others have) after the 3rd restart. (Still seems like something needs to warm up... its now "winter" here +- 5degC at night/early morning) Once it works it seems to work fine (as it did even with 2.35). My R's are shorted. Using "15min IAC".

Post by **grippo** » Thu Jun 08, 2006 10:40 am

Ballistic,

In thinking about this problem, I came up with some questions that might help narrow down the problem:

1. if you repeat your pintle extension measurements, can you duplicate what is happening in the car in the sense that if you set the stim so the temperature is say 50 deg and slowly (say over a minute or 2) move the temperature up to 168, vs restart with the temp left at 168 does the pintle end up in the same place assuming the step positions are the same, as they should be for the same temperature ? If so, that is the pintle ends up in different places as it does in the car, this takes starting temperature out of the problem and means either the electronics don't work right with your motor when it moves in small steps vs large steps, or we may need to factor in acceleration in the software to make it work right. I know velocity doesn't matter in your case, but acceleration is a different factor and can make a difference at least in bigger motors.

2. If the pintle ends up in the same place whether cold start or hot restart, then can you put the motor in the refrigerator for a few hours and then repeat the test ?

3. The only other factor I can think of is maybe mounting stresses on the motor which relax after the engine is warmed up.

ae1969 · Post by **ae1969** » Fri Jun 09, 2006 6:22 pm

MY experience: IAC now WORKS as described.

I had my jeep IAC all wired up and it seemed to be working but very erratic as everyone has described. I confirmed and re-confirmed the settings on the Jeep IAC and I would get the IAC repositioning itself, going the wrong way, vibrating etc..et.c.... going NUTS

So I tried the 'jumper on the resistors' NO GO.

SO I bit the bullet bought another Jeep IAC and a GM IAC. The jeep IAC has 50 ohm coils and the GM one had 60 ohm coils.

I alternated the wiring in all combinations for each IAC. The two JEEP IAC would work erraticly. THe GM one worked fine.

The GM one worked at a step size of 10 (~ 14 mm) 200 (~25 mm)

I am starting to wonder if there are subtle differences in the IAC's that work with different settings?????

hippled · Post by **hippled** » Fri Jun 09, 2006 7:35 pm

I am having the same problem with the jeep IAC. Going to buy a GM one and try that out. Seams like a quick and easy fix. I am running MSII on a V2.2 Board with 2.36 code and using MT2.25 for software.

Dave

P.S. I like the custom IAC mount ae1969. Much easier then machening one.

Philip Lochner · Post by **Philip Lochner** » Sat Jun 10, 2006 6:48 am

I have "Retired" my IAC. With 2.35, everything worked fine except I had to restart every now and then. With 2.36 things just seem much more inconsistent to the extent that it frustrates me so much that I've decided to switch if off. If/when rpm based IAC control is available I'll try again.