Power Loss after Freeway Drive

cjoenck · 09:56 AM

It's about 8F outside and my '91 C2 starts fine, runs well, no issue. I take it on the freeway for about 30 minutes of uninterrupted 60 mph drive. After getting off, the car starts to stall with no power, no response to accelerator. The "Check Engine" light comes on - never a good sign. So I limp along for maybe 5 minutes and suddenly everything is back to normal. The "Check Engine" light goes off and all is good again.

I am thinking in this order:
- Idle control valve stuck due to extremely cold air - any moving parts in there?
- Engine temp sensor going bad
- MAF sensor - good point below, just hope it's not this one since replacement is expensive....
- Distributor belt - unlikely since it is an intermittent problem

The roads were dry so water causing electrical problems is a more distant posibility.

Since I am not looking forward to working this issue while it's freezing outside - my garage is not heated - any insight is most welcome. Thanks

AM993 · 01-23-2008, 08:10 AM

Maybe you want to add "MAF sensor" to your list of potential issues.

Atlantic07 · 01-23-2008, 01:38 PM

Yes, the Idle Control Valve has moving parts (I just cleaned mine - very easy - check the DIY here)!

I don't know too much about the tech details (despite the fact that I own a 91 C2

, but it sounds to me like a fuel supply problem. I had such problems on other cars and it showed the same symptoms. What happens if you suddenly accelerate on the freeway - loss of power would confirm my suspicion?

Good luck!

cjoenck · 01-23-2008, 02:11 PM

Thought of that - car is fine accelerating on the freeway, no issue, no loss of power. I guess it could be a blocked fuel filter. I was thinking ISV because it sits pretty expose at the top of the engine so it gets blasted with extremely cold air. After 5 minutes the engine heat has "thawed" the valve and it snaps back.... Not sure that makes sense. I guess the same applies for the AMF sensor as well.

DW SD · 03:23 PM

Can you more accurately describe the symptoms when it loses power? Does it still stay running, but just at idle? will it rev up in neutral? Does it stumble, miss, shake, OR?

I was thinking possibly your fuel pressure regulator stuck open (reducing fuel pressure, though I've never actually experienced something like this).

I'd rule out the distributor belt, probably the fuel filter, neither are intermittent and would be most acute under load. The idle air controller seems unlikely. Even stuck wide open, it should have decent power at the top end. It just wouldn't drop to low idle.

Doug

cjoenck · 01-24-2008, 06:13 AM

Hmm, good point. I guess it could be fuel. When I come to a stop at a red light after getting off the freeway, idle rpm just drop through the floor and the car dies. However, it does come right back when starting. I can prevent the car from stalling by shifting to Neutral and riding the gas pedal. Trying to accelerate away from the light, it feels like the car is not responding at all, really just limping along. The "Check Engine" light is on at this time. The best way to describe it is trying to accelerate from a stop in forth gear.... Engine is completely unresponsive. After 5 minutes, everything is back to normal. This only happens after some time on the freeway. Just city driving - even in subzero temperature has not brought on the problem yet. It's strange but your standard "does not start / idle when cold scenario" does not a apply here. The car starts and idles fine in the morning after 24 hours a 14F garage.

DW SD · 01-24-2008, 07:28 AM

It almost sounds like the engine is going into some sort of limp home mode. If it is not shaking violenty (as if several cylinders are out) then I would venture to guess some electrical component is failing, as in a sensor. I think if the fuel pressure dropped, it would run extremely lean, but would miss shake, etc, as well.

I may guess: hall sensor in the distributor, MAF, possibly crank position sensor (though it seems like it wouldn't run at all, if that crapped out). ALSO: I wonder what would happen if the idle switch remained engaged (as if throttle is at idle), even though you were wanting to accelerate away from stop? If it happens again I might check this first with a continuity meter.

I think the computer stores the codes, since it ignited the check engine light, can you pull the codes? I think you need a BOSCH Hammer or similar to interface w/ the computer.

Doug

DW SD · 01-24-2008, 10:09 AM

check out the 964 throttle switch picture on this thread:

Throttle-valve switch: how to check

cjoenck · 01-27-2008, 08:14 AM

As a first step I pulled the ICV yesterday morning and it was dripping with oil on the inside - not a good sign. So I cleaned it with carb cleaner and let it dry. While I was at it, I also cleaned out the muffler attached to the ICV. It had a lot of oil in it too. I am pretty sure the oil caused the idle problem after freeway driving in cold weather.
The very cold air made the oil residue in the ICV more "sticky" preventing proper operation. Once the engine had heated the oil again in city traffic, everything went back to normal.

Of course I face a bigger problem now with oil probably in the entire intake system. I hope I can leave that for a warmer day. Will I damage anything if I leave that service until it is a bit warmer in my garage?

Thanks!

DW SD · 01-28-2008, 12:56 PM

Well, that was simple. It must have been stuck shut. You may want to adjust base idle, too.

Sounds like your oil level is too high.
Buy some Air Flow sensor cleaner to clean out your MAF and use brake cleaner or the same fluid for other components. Any that has sensors, use the Air Flow sensor cleaner. It is safe for electrical components.

I would clean up when you can. I know oil film will ruin the later 993 (hotwire-type) intake air flow sensors.

Doug

cjoenck · 01-29-2008, 03:56 PM

The story continues. I just pulled the error codes and I get a "21 - Hot Film MAF" from the DME and a "21-RPM Signal" from the Tiptronic. I guess the Tip signal could be secondary fault but the DME code is an issue. I will pull the MAF and clean. Hopefully that is enough - I am not looking forward to a new $1300 part....
Thank you for all the insight and help.

aigel · aigel's Garage

I was going to say to pull the codes before you do anything. Glad you did. How does the MAF on the 964 work? Make sure you clean it properly ... and as others have mentioned, overfilling is likely the only reason why you'd have oil in the intake.

George