Subaru wrx version 5 idle sticking

[bdearnley]

I asked this question on Ray Hall's old forum and got some helpful advice, but I still can't completely eliminate the following problem. ECU is PnP.

When the car has just been started and I drive away within a few seconds, the next time I come to a stop the idle is high, by 100 or so rpm when hot, and more when cold. I can correct this by forcing the revs down by letting the clutch out a little with my foot on the brake until the revs are just below the correct idle speed, then pushing the clutch back in.

I believe this is something to do with the Subaru stepper motor not being able to give feedback to the ecu as to exactly where it is, or some other problem of the ecu controlling the stepper motor. I also seem to recall someone mentioning this is caused by anti-lag cooldown idle settings or something like that. I don't have antilag enabled. Correct me if there is some other cause.

I have reduced the problem slightly by reducing the control range of the IAC, which was Ray's advice, but this is the only irritating problem I still have. Otherwise the car drives as smoothly as factory, and I'd like to get this aspect just as perfect.

My IAC settings are:

Control range: 2600
Adaption Rate: 1000
Dynamic Comp: 30
Stall Saver: 1
Reset Engine speed: 4500 (What is this?)
Fuel Compensation: 12.0
TPS Limit: 1.0
RPM Limit: 0

Idle ign timing:

750rpm: 20
850rpm: 10
950 rpm: 5
2000rpm: 25
2500rpm: 30

Idle speed is 875 at all battery voltages, with idle valve open 5% - 10%
AFR at idle is 13.8
Idle is smooth and stable.

If I wait about 30 seconds before driving off then the problem doesn't occur. I thought it might be the P-S Fastidle Timeout, but reducing this to 0 doesn't help. Is it something to do with the P-S Fastidle inc or Timeout?

If anyone has any tips I would greatly appreciate it.

[Ian]

I think this could be related to the Stepper motor settings. Could you post them also please so we can check them.

[bdearnley]

Ah, didn't think of that. Here is my Stepper setup:

Stepper motor: Enabled
Set direction: Reversed
Preferred-dir re-cal: Fully closed
Power up re-cal mode: Preferred-dir
Stepper travel: 220 steps
Smart re-cal count: 20 steps

[Ian]

The stepper settings are good. Without seeing what the IAC position parameter is doing after the starts I would make the following observations;

The idle control function in an SMC / SM2 is significantly simplified compared to an SM4 (with far less ways of really making a mess up of things) but this means there are limitations also. But in all cases the Idle control is frozen when the TPS limit value is exceeded, and it maintains this position until the TPS drops below the TPS limit value.

I think perhaps the IDLE timing ramp (between 950 & 2000 rpm) in combination with a bit of unsettled IAC valve position being held after drive away is responsible for what you are seeing.

Can you get a PC log (set to F8 Manual control) from before start to the problem occuring, including your clutch action to rectify the idle. You should record IAC Setpoint, IAC Valve position & Stepper position in addition to the normal parameters. You might be able to replicate without driving by keeping the throttle open for about the time you would drive before the first stop where you see the problem.

[bdearnley]

Hi Ian. I noticed in the Subaru cal file posted on this forum that the Smart re-cal count in the stepper setup was 25, whereas mine was 20. I have changed mine to 25 and since then (2 days) I have not experienced the problem I described in my first post. This doesn't necessarily mean I have found a cure, but I won't be able to log it unless I can replicate the problem. If it happens again I will log the parameters you mentioned and post it. It's interesting what you say about the idle control being frozen after the TPS value is exceeded - this goes some way to explaining why this problem sometimes occurs. I might also bring down my idle timing at 2000 and 2500rpm.

[Gert]

I believe this is something to do with the Subaru stepper motor not being able to give feedback to the ecu as to exactly where it is, or some other problem of the ecu controlling the stepper motor. I also seem to recall someone mentioning this is caused by anti-lag cooldown idle settings or something like that. I don't have antilag enabled. Correct me if there is some other cause.

If anyone has any tips I would greatly appreciate it.

No tips, just sharing.

I have exact the same problems. This is with an SMC with Bosch 2 wire valve.
Like you said, if you start driving immediately, idle stays too high.
I can drive for about 30 minutes, and if I stop somewhere, traffic light or so, and the throttle isn't touched long enough, idle comes back to normal.
Shutting down the engine, and immediately starting again, solves it too.

To me, it looks like some timer problem.

Gert

[sl1000]

Hi,

This is a more common problem with the PnP impreza ecu's.
I have done an enormous amount of logging's checks etc.. to find out the problem.
This is my conclusion so far:
The Idle control regulation within the ECU only works IF

- throttle is below setting:TPS limit and
- Anti-lag timer is 0

this Anti-lag timer is set to 100sec when throttle is above TPS limit and reset to zero when engine RPM is equal or lower than current idle target. Also it starts counting backwards when throttle is below TPS-limit.

what happens is when the engine is just started cold. The idle target is increased let's say 1200 rpm.
Due to this and also the cold engine the stepper needs to be set fairly open (for example 50%)
Then you drive off and during this drive the engine warms up, Also the ecu remembers the last stepper setting and doesn't change it while the engine is not idling (above conditions).
Then you need to stop at a stoplight or something, and the target is reduced in the mean time to for example 800 rpm due to the warmed up engine. The stepper is still at 50% although the TPS is below the setting the idle is not close enough to its target thus the timer is not reset and the ecu just doesn't regulate the idle. At this point the timer has started to count to 0. only when the counter hits 0 then the idle control start regulating and normal idle is resumed.
If you force the engine down in rpm with the clutch then rpm of the engine gets close enough to its target and counter is reset and normal regulation start.

Problem is the timer is hard coded into the ecu. and little can be done about that. ( you can see the value with monitor all)
The solution Ray suggested only marginally works. but some settings can make it better or less common.
by example reduce the fast idle settings as much as possible
also reduce the regulation speed dramatically down. (set adaption rate to 100).
also make certain that stepper is near 0% when engine is idling completely hot by manipulating throttle plate stop. (remember to calibrate TPS-sensor).this will prevent the engine from stalling.
set TPS-limit not to low. > 1%

And who said only Microsoft had bugs in their software.........:(. I wish autronic would do something about this bug, because its bugging me...........

so there is nothing wrong with your idle stepper it's just the ECU. but by some tweeking of the parameters you can make the problem less.

hope this is of some use

Bart

[bdearnley]

Thanks Bart.

I had the problem again yesterday so opened the laptop to attempt to log it, but then could not replicate the problem! So it is intermittent. I admit it is not bad, but I think the general consensus is that it is something to do with the antilag timer. Can't believe this can't be changed to 0 in the software... oh well. I will try changing the IAC adaption rate down to 100 like you said, and play with lower fast idle values. My stepper hovers between 0% and 10% when hot, so I think that's OK.

[sl1000]

O one other thing. if you wish to reproduce the problem to see if the settings are better try this.

with the car idling. load the engine just a bit with the clutch and watch the stepper opening. The ecu will react with higher stepper to get the idle back on target. now without unloading the engine increase the rpm by giving it some throttle (above TPS-limit). Watch the ALS-timer it now is unequal to zero.now let go of the clutch and reduce the throttle gently back to zero. If the problem exists the stepper opening is still high throttle is close to zero. and the ALS-timer is counting backwards. rpm will be above normal idle. leave it untill the timer is zero. than rpm will fall back to normal target.

[bdearnley]

This sounds like I will need 3 feet to do this! Or maybe just some heel/toe-ing...

Or maybe just use the handbrake ;)

[Ian]

Anti lag timer !!! Something is wrong with a setting / s in the calibration. Can you send me your calibration please Bart.

mailto:customer@autronic.com.au (customer@autronic.com.au)

Regards. Ian

[sl1000]

Ian,

Cal file has been send.

bdearnley : yep just use the handbrake and or put it into high gear, or park the car against a wall :D

It is best to try with laptop connected and displaying all parameters. then you can see for your self what's going on...

Bart

[Wroom]

Well, i have seen this problem and reported it a long time ago. Since it is not fixed on the SMD's the problem may not be so easily curable i guess?

It is related to stepper idle motors only.
The problem does not exist with the SM4. Only the SMD PNP's.

Countermeasures:

Stepper engine must be in excellent condition.

Set TPS Limit to 5%.

Be sure to have a good battery in the car, since low voltage over the stepper causes this.

Use "smart recal" with a setting of about 30.

Use a low PWM rate.

Use an aggressive idle ignition ramp.

Unturn the idle air screw so that the idle stepper goes to close when engine is warm.

If you have HI/LO cooling fans then get hold of a fan controller to smooth start the fans. The inrush current to these fans can cause the stepper to "miss a step or two" and when it does, the ISC will think the stepper motor is at a different position than it really is.

Make sure the ground wiring to the ECU is good. Cars like the Mitsubishi EVO6, that have wiring "optimized" for low weight suffer the most for with this problem. While the EVO4 that has fatter ground wires to the ECU seem not to have the problem.

Best fix for this problem is to go for the SM4.

[bdearnley]

Just reporting a quick update regarding this issue. Since I changed the IAC adaption rate from 1000 to 100 two months ago I have not had this problem, even slightly. So I believe this is the cure.