IAC stepper is fried, alternative doesn't work either

[Arthur]

Hello

I hope you guys can help me. I'm just starting to write my maps. I started the engine in a jig in my shed weeks ago. I have a self made carbon manifold, which needs an extra layer of epoxy. It leaks a bit so my rpm was minimum 2000. I put it on spark cut base idle and then it run the desired rpm, but sounded a bit like a fuel race engine because of the spark cut based idle. Sound legit right. It ran good enough to put the engine in the car.

Now in the car, it is different. Idle totally changed. Checked my stepper and it does nothing. I think I fried my stepper chip. Switching the fuel relay with stepper also didn't work, so the chip must be gone.

But when I remove the stepper and go for spark cut idle, still no change. More - less advance, also no change in idle roughness. It sound like it runs on 2 cylinders or like it has an 300+ cam, very rough. And with the stepper removed and 100% bypass air, it should go to 4000 rpm IMO.

When i give it some rmp on the throttle, it sound good. Only back on idle it sounds very rough. Vacuum is only about 80 kpa.

A bit obvious that you have bad vacuum, when the manifold leaks. But I have got it down to only 600 rpm as it is, with good lambda, but still very rough and only 80 kpa.

This puts me off. If it was only due to the (small) leaks in the manifold, I would have trouble getting low rpm, right. Could it be that I miss something else that makes idling very rough? Now in vemstune it only runs when I set the idle control to stepper, but when i set it on spark cut based, it doesn't even run. What idle control should you choose, when you use spark cut based idle? You can choose stepper, on-off and pwm, but you use non of them with spark cut based idle, right?

I need to order a new stepper chip, but I would like to use spark cut idle for a while so I can at least start tuning the ve and rest. At the moment it's almost impossible to drive.

[Kamuto]

Hello

I hope you guys can help me. I'm just starting to write my maps. I started the engine in a jig in my shed weeks ago. I have a self made carbon manifold, which needs an extra layer of epoxy. It leaks a bit so my rpm was minimum 2000. I put it on spark cut base idle and then it run the desired rpm, but sounded a bit like a fuel race engine because of the spark cut based idle. Sound legit right. It ran good enough to put the engine in the car.

Now in the car, it is different. Idle totally changed. Checked my stepper and it does nothing. I think I fried my stepper chip. Switching the fuel relay with stepper also didn't work, so the chip must be gone.

But when I remove the stepper and go for spark cut idle, still no change. More - less advance, also no change in idle roughness. It sound like it runs on 2 cylinders or like it has an 300+ cam, very rough. And with the stepper removed and 100% bypass air, it should go to 4000 rpm IMO.

When i give it some rmp on the throttle, it sound good. Only back on idle it sounds very rough. Vacuum is only about 80 kpa.

A bit obvious that you have bad vacuum, when the manifold leaks. But I have got it down to only 600 rpm as it is, with good lambda, but still very rough and only 80 kpa.

This puts me off. If it was only due to the (small) leaks in the manifold, I would have trouble getting low rpm, right. Could it be that I miss something else that makes idling very rough? Now in vemstune it only runs when I set the idle control to stepper, but when i set it on spark cut based, it doesn't even run. What idle control should you choose, when you use spark cut based idle? You can choose stepper, on-off and pwm, but you use non of them with spark cut based idle, right?

I need to order a new stepper chip, but I would like to use spark cut idle for a while so I can at least start tuning the ve and rest. At the moment it's almost impossible to drive.

spark cut idle control must be disabled use fuel cut for that.

[Arthur]

Oké

Yes I turned off fuelcut (by setting it on 5000 rpm). Strange that spark cut idle doesn't work. When due people use that than?

[Kamuto]

Oké

Yes I turned off fuelcut (by setting it on 5000 rpm). Strange that spark cut idle doesn't work. When due people use that than?

spark cut idle kills your spark plug in 10 minutes

[Arthur]

Aha

It turns out my stepper coils are A - D and B- C, so I swapped two wires and the stepper is alive now. Turn out the chips might not be freid.  Used some ducktape to make the vacuum better and I now reach 30 kpa. stepper stays on min steps allowed, but sometimes opens a bit, while the rpm is still too high, still at 1800 orso.

At least it makes a bit sence now. I have to solve the leaks first.

[Arthur]

Hello

Some time passed now and I'm back on this subject. It turns out my control valve was worn. I fitted a new one. Vacuum leaks are gone now, but still some issues.

I'm can't really get to fine tuning, because getting it to run drive-able is still a bit hard. It drives, but very rough. I do get stable idle sometimes, and I can see the idle drops down with rising temperature. Only when raise rpm and iac needs to pick up, it almost dies before the idle valve really works. I tried to quicken the valve and also set PID, using small value I. Max step close is "1" and this is really needed to close 100%. But several times i have seen idle rpm about 500 above setting with the valve on step 18 or 19. I assume that the valve should move closer to step 1 when the idle is high, but it doesn't. What can this be? I have a feeling that dying on low rpm is more due to mixture / accell enrichment then due to the speed (or lack of speed) from the valve.

Can someone tell me how accell enrichment works on idle valve?

[Arthur]

Hi

Is my question so hard or is my description so bad?

I have put a rubber shrink for electric wires on the idle valve seat. It turns out the idle valve didn't close very well on the seat what didn't help idle.

I still don't get how the idle valve control works though. On rich mixture it will run quite good and on 900 rpm as set in vemstune. To lean and it will stall. Idle valve cannot act fast enough to get the idle up when the mixture is lean. Mostly the valve is on step 7 or 8 and the minimum is 1. The engine seems to need very little idle air when warm. But sometimes the valve is on 17 to 20 all of the sudden. It looks like when the engine stalls, and you start it directly, the valve does not have time to set check fully closed position.

Does anyone know how the idle valve ref table really works? I can only get the engine to 900, when I set the ref table very low (1). But then it stalls often at red lights. But when I set the ref table higher, it doesn't stall, but idle is 1200 while the valve is also on step 7 or 8 like before.

I would think the ref table is a reference point only to start from when idle control starts. It seems to do much more then that though.