Could an ISV fault cause a stall at highway speeds?
 

Hi Everyone,

Well, I am here in Chicago, transitioning from the working world to the life of a grad student (ie, no more salary).

If you remember, about a month back I had an issue where my S4 was stalling about every two minutes at highway speed (after being on the highway for about 40 minutes or so). In the city, no problems at all -- it was strictly at speeds above 50mph or so.

Well, for the past month, the car has not stalled once. Granted, it has been mostly city driving, with a few highway trips thrown in -- but less than 20 min each.

This past weekend, I drove from Chicago to Iowa for a wedding, and the dreaded stalling returned. This time, I was at the wheel instead of my Dad, so I was able to experience it firsthand. Basically, after 40 min into the drive with no problems, the CEL came on and the car stalled immediately. After coasting for 30 seconds, the car started back up. It then repeated the problem about every two minutes: stall, coast for 30 seconds, start again.

I started experimenting with a few techniques. What turned out to be succesful was this. Every minute and a half, I would take it out of gear, let the engine go down to idle, then put it back in gear and go on my way. I was able to drive for an hour this way with no stalls, until I forgot to put the clutch in, and two minutes later...stall.

The last time this happened (a month ago), I was unable to get my VAGCOM to work, so this time, I jumped the connections to flash the codes on the CEL.

I got the following: 2231, ISV fault.

Could an ISV issue cause this particular symptom?, particularly as it only happens at highway speeds? What does letting the engine go down to idle do that would cause this to not stall?

Of course, the other thing is that a month ago, I had replaced the coils with the 034 conversion right before the drive. I have not swapped them out yet. I may do that tonight and go on an extended drive tomorrow to see if it might be the coils.

It's weird. Any thoughts would be appreciated.

Thanks,

Adam

I would say unlikely
 

seems that it would represent too small an addition of air to the intake charge to cause a stall....but If you are at 2000rpm, maybe it is enough air. Just some food for thought.

What you have done to diagnose since last time?
 

Did you replace the fuel pump?

Since last time...
 

...I have done the following:

1) Gone through three tanks of gas. This likely rules out that it was a bad tank caused by the 12-year old can of Lubro-Moly Ventil-Sauber.

2) Had the Viper alarm installation checked by Best Buy for any wiring errors -- they found none.

3) Checked the ignition switch for damage -- it is good.

I have not replaced the fuel pump, which has 50K miles on it. Today I am taking out the 034 coils and swapping the OEM coils back in and going for a long drive. Will report back later.

Thanks,

Adam

ISV just bypasses the throttle. It doesn't add unmetered air
 

But if you get off-throttle at highway cruising, the ISV should crack open some. Does it always happen when you lift off-throttle at highway speeds? Or does it happen on throttle or partial throttle at highway speeds?

Typically, the ISV won't matter as even the slight crack in the throttle body is enough to prevent stalling when off-throttle so I don't think its the ISV either.

My guess its an ignition or timing reference issue.
Without the factory coils in there, will the ECU throw proper ignition codes?

you let Worst Buy touch your car? eh...lol