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Car Dies When Letting Off Hard Throttle

gilber33

New member
Joined
Jul 7, 2009
Location
Milwaukee
Driving a 1993 940 Turbo.

When I am under hard throttle and let off the gas quickly, the car dies. Most notably as I accelerate from a stop sign and need to stop quicky, the car dies. It always restarts right away.

My only idea is a cluster I just put in reads rpms really wonky. The needle fluctuates. Sometimes at a stop it will read zero. I know the ecu gets some readings from the cluster, so maybe that's messing with it. This never happened before I did a series of repairs one of which included putting this cluster in because the previous one had a bad speedo. Nothing else I did would have affected this. Strong vacuum, new intake gaskets, etc.

Any input would be appreciated.
 
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Does the cluster theory sound plausible to anyone? I also put in a used IAC at the time. Maybe it's not 100% working and not opening fast enough?
 
Audibly the TPS is set correctly. But maybe it needs to be played with as well as the linkage. That's the most common time it dies; letting off the gas after a burn out.
 
Your rev needle fluctuates and your car dies on hard deceleration, right?
That could be a cracked Crank Position Sensor giving up when flexed forward under deceleration.

My only other idea is a dead recirc valve ontop of the turbo, which is easy to check by removing it. Three bolts.
 
My '92 945 turbo did exactly this with a cruddy IAC valve. I just cleaned it with carbon dissolver and the problem went away.
 
Audibly the TPS is set correctly. But maybe it needs to be played with as well as the linkage. That's the most common time it dies; letting off the gas after a burn out.

Base idle is off

To set it correctly:
1 car idling, clamp hose to IAC (assuming IAC valve is not full of ****).
(1.1 car will stall)
2 adjust throttle stop screw (not the linkage) to get a solid 450-550 rpm. Better lean to the high side
3. adjust throttle position sensor
4. profit
5. remove clamp from IAC hose and idle should return to what the ecu is set to (700-900+ depending on coolant temp)

Sometimes you need to go through steps 2-3-5 two times to get it right.

Worked on my B230F+T, it would stall after boosting (so basically al the time)
 
Your rev needle fluctuates and your car dies on hard deceleration, right?
That could be a cracked Crank Position Sensor giving up when flexed forward under deceleration.

My only other idea is a dead recirc valve ontop of the turbo, which is easy to check by removing it. Three bolts.

It does fluctuate a little bit, but not always. How does the cps flex forward under decel?

And as stated earlier, I'm running a K24 that had a good recirc valve and now the car has a new Turbosmart recirc valve and the issue is the same.

My '92 945 turbo did exactly this with a cruddy IAC valve. I just cleaned it with carbon dissolver and the problem went away.

The IAC is a new used unit that was very clean internally. I got a can of carb cleaner to clean it out just in case.

Base idle is off

To set it correctly:
1 car idling, clamp hose to IAC (assuming IAC valve is not full of ****).
(1.1 car will stall)
2 adjust throttle stop screw (not the linkage) to get a solid 450-550 rpm. Better lean to the high side
3. adjust throttle position sensor
4. profit
5. remove clamp from IAC hose and idle should return to what the ecu is set to (700-900+ depending on coolant temp)

Sometimes you need to go through steps 2-3-5 two times to get it right.

Worked on my B230F+T, it would stall after boosting (so basically al the time)

The more I've been thinking about it, I think you're right. This all started after I did the new TPS and IAC and messed around with the throttle plate and linkage a ton and I think I set it so the plate would be fully closed with the foot off the gas. Which, is wrong and the car I think is idling at 400ish. During this time the car ended up being my DD so I couldn't really mess with it and I was busy dealing with other crap and then I pulled the engine to deal with an oil leak and then it was winter and then I moved. So I'm finally getting back to looking at it.

. I will do this process.
 
Got the car warmed up and idle was about 500, so too low. I will adjust the throttle plate to get the rpms up.
 
It does fluctuate a little bit, but not always. How does the cps flex forward under decel?
It is a wire joining the top of the bellhousing to some connector up on the loom.
If it is craccked the natural flexing from left, right, braking can make it fail at wierd times.
I had one like that.
New one solved the problem permanently.
 
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