MS2 4G63 Idle Control Problem

[wishihadatalon]

Hi guys,

After many issues getting my car running with megasquirt, I am starting to get my car dialed in and am having a few issues with getting the car to idle correctly. I have the fueling and timing to be what I consider stable, but for some reason, I still have some hunting for idle target. The car will idle great for a few seconds and then it will drop 200ish rpms, over shoot target, and then come back down. I for the life of me can not figure out why this is happening.

One thing I believe I may have to address mechanically is the factory fast idle air valve which uses a spring loaded plunger that closes as coolant temp rises. This system should be extremely consistent so I don't believe it is a problem, but I'm still going to block it off.

Also one final issue. Sometimes when I do small throttle blips in a backing the car out of a parking spot situation, when I let off, the valve opens way up and hangs the idle until it enters closed loop idle.

Can anyone provide a direction for me to investigate? MSQ and small log attached.

Thanks for any help,

TJ

[kjones6039]

the factory fast idle air valve which uses a spring loaded plunger that closes as coolant temp rises.

From the msq you posted it appears that you have idle control set to use a 4/6 wire stepper motor................ That isn't going to work with the IAC you described above!

or....... did I read that wrong?

Ken

[CRSTune]

No, he means the thermal fast idle valve, which adds additional air when cold. It's a separate mechanical air bypass valve. The 4G63 does use a stepper IAC valve.

[wishihadatalon]

No, he means the thermal fast idle valve, which adds additional air when cold. It's a separate mechanical air bypass valve. The 4G63 does use a stepper IAC valve.

That is correct.

On my drive to work this morning there was more/worse hunting and hanging after letting off of the throttle. I may take the throttle body off tonight to close the fast idle valve and swap the stepper motor with the one I used for bench testing.

[kjones6039]

No, he means the thermal fast idle valve, which adds additional air when cold. It's a separate mechanical air bypass valve. The 4G63 does use a stepper IAC valve.

Got it! must be my dementia kicking in!

Sorry to intrude.........

Ken

[turbo conversion]

From what I can see in the data log you need to achieve a stable idle with warm up only first.

Once you do that then you can start tuning idle with closed loop.

Trying to tune closed loop before achieving a stable idle with warm up only just compounds the unstable idle.

Also you said you were going to block off the fast idle air valve, I would recommend that as well.

David

[rukavina]

While you have it apart do some testing on step direction and step count. It's a lot easier to do when you can see and touch the pintle

[wishihadatalon]

While you have it apart do some testing on step direction and step count. It's a lot easier to do when you can see and touch the pintle

That's what I did with an extra stepper motor, but the one in the car didn't seem to be working the same way as the one I used for bench testing. For most consistency, I'll bench test whatever one goes in the car.

Thanks,

TJ

[wishihadatalon]

Hey guys, I got the car put back together tonight after eliminating the factory mechanical fast idle valve. I was able to get it to idle at a pretty consistent rpm, but I found the method to be quite weird. I set the idle control to open loop and when it got up to temp with the target step count at 30 steps, I set the idle to 950rpm with my idle adjustment screw(higher than I want but I can live with it). I had to turn on the idle advance setting and had to double the timing values from my target idle to 700rpm and then an additional 5 degrees lower than 700rpm. With this, the idle will fluctuate +/- 40 rpm which I am fine with. This also produced a steady AFR value which I've struggled with. Does this make sense to anyone? Having such a large timing change in such a short period of time seems wrong to me as it isn't consistent with my previous experience. BTW, I'm beginning to wonder if the cam shafts in the motor have some weird overlap issue. They were with the car when I got it so sadly I don't know what their specs are.

[rickb794]

You are not trying to idle it at 14.7, are you?

[wishihadatalon]

You are not trying to idle it at 14.7, are you?

I was, but have come to the realization that I am not using sequential injection. I have since got it to idle rock solid though it required what I mentioned above. Now I'm just fighting through random idle hangs when the car is in warm up mode and getting the rpms to not dip when I let the rpms fall from cruising to idle. I've played with the idle valve closed feature and have found it to be very inconsistent on my car. I'm not sure if the valve is too slow or I don't have a setting right but sometimes the idle would come down nice and controlled while other times it would slam down and barely catch itself. For now I am driving with the valve never closing and dealing with the slight hang during gear shifts.

[turbo conversion]

Try changing Power Between Steps to Always On instead of Moving Only.

Also set Idle Valve Closed Steps to 60 instead of 0 as the log shows idle steps to be around 70.

David

[wishihadatalon]

I just wanted to give an update. After having to deal with a clutch master failure, I had the car in the garage and decided to start from scratch on this. What I ended up finding was that I had 250 steps to home the valve and also 250 to open the valve. This was way too high for the valve. I learned (again) that the open step count for the DSM stepper is 140 steps. After adjusting the open and closed steps, it was much better. Ultimately this was causing inconsistent recovery steps when the valve would close while driving or shifting.

As a final measure, I figured out that I had the Idle Ignition Advance set to turn on before the idle reached up to temp target idle. This was causing the idle timing to be severely retarded and the motor was trying to compensate. After figuring this out and setting the valve back to moving only, the car seems to be rock solid.

Thank you for all of the help guys,

TJ