1989 260E has always stalled. What needs replacing?

Anyone familiar with the 1989 260E engine? We've had the car since new. Only has 65k. Anything it ever needed was done pretty much on time, even the 10-year makeover. But it's had a problem from day 1
which two dealers can't identify, and we're told there's never been a service bulletin about this.
When the outdoor temperature is in the 60s or 70s, and you take your foot off the gas in the 30 to 40 mph range, the engine occasionally stalls immediately. The tach goes right to zero. Something that is supposed to prevent stalling by kicking-in for idling occasionally sticks. Happens two or three times a month. Prior to this year you could restart immediately. This year we must let it sit for 20 to 30 seconds or it won't re-start. Whatever is sticking is now sticking a bit worse, and takes 20 to 30 seconds to un-stick.
We'd like to fix it, as sitting immobile for 30 seconds in a busy intersection is bad form. It's also not a great idea to negotiate turns with no power steering, even if it's only at 25 mph.
It doesn't happen often enough to be able to isolate the bad part, but we're not in position to replace each little temperature sensitive fuel and vacuum gizmo under the hood that affects the idle.
If this was your car, which gizmos would you replace, and in what order? IOW which are the most likely parts in the fuel and vacuum circuits to stick a few times a month and affect the idle?
Much appreciate your ideas. FWIW the brand of gasoline is immaterial. We usually burn Amoco premium but it happens regardless of what's in the tank.
Rey Barry Charlottesville VA snipped-for-privacy@cstone.net
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Certainly you don't want to pay for "let's try this and if it doesn't work we'll try that"
I've read your post several times and had a different suggestion with each reading. I disclaim any intimate knowledge with 2.6L engines but do understand how engines work and have a bit of knowledge of some reasons for their failures.
1. If this were a carburated engine and the ambient temperatures at which failure occurred were in the 50s I'd say carburetor icing - or lack of preheated intake air - were the cause. Discount this.
2. The electric fuel pump is powered by a relay that acts like an intelligent switch for the fuel pump. These relays get intermittent with age and cause similar failures. But their failure is usually quite random, your car's is quite related to specific events. Discount this.
3. There's also an "overload protection relay" that sometimes causes odd behavior but the same discounting as in #2 applies.
I don't believe the problem is vacuum related - vacuum leaks are constant. I don't believe the problem is fuel system related - there would be other occurrences. The problem may be electrical but it occurs with too much certainty as to environment, discount the usual electrical - coil distributor etc..
4. BUT, the system / device that controls the idle speed is highly suspect. An on-line catalog shows an idle control valve. As it appears to be a mechanical device perhaps the original valve could be checked and cleaned and its input sources checked to ensure they are viable. Of course one can always buy a new valve - $188, Bosch.
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A mechanical valve problem is the best of all answers. Since it's been doing this since the car was new and has been no worse, no better through 15 years, we may be looking at a valve with a very minor fault, perhaps something a little careful filing can fix.
I'll check the on-line catalog and the CD.
Thanks, Rey
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You need the air/fuel messuring position sensor. I'm certain about this cause I'm sure the odle speed cylinoid was probably replaced once or twice in an effort to fix the problem but it didn't, am I right so far?. I'm sure you've seen your engine with the air filter off, well right underneath it is the big round 3inch diameter plate, as you excelorate the vacuum created draws down that plate which opposite end is connected to the fuel distribitor, the two are connected by a piviting arm. Tp make a long story short cause I'm sure you don't care all that much about the details. The piviting has it's own sensor, the cars computer wants to know at any given time hwta position that plate is in. When you let off the gas pedal the idle speed system is suppossed to kick, and you and the dealer both assume it isn't, well the problem is it is kicked in, allowing too much air at the moment that you let off the gas pedal, the sensor is not letting the computer know that the car is at idle. If you disconnect your idle speed cylinoid for a month you will notice that car is not cutting off anymore. To fix this you need to replace the entire housing that mounts the fuel distruibitor, the housing includes that plate in question, this is quite expensive, I think $ 700 in ports, Bill correct me if this figure is wrong!!. 3 years ago my parts supplier carried just the sensor, it was a bit tricky to install it, but only $50.00. you can go out and get some other opinions, but nothing will fix it but the sensor, good luck and keep us posted. Martin. Autobahn Auto
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snipped-for-privacy@aol.com (Bnzmn600) wrote in message

That seems reasonable but it's actually all original. Nothing has been replaced. Since the problem was with the car from the beginning and the fault happens so rarely, the mechanics can't tie this scenario to a particular part. There's no wear or aging involved, and the idle system operates correctly 99.x% of the time.
I was hoping that the fact that in the 15th year the sticking, while no more frequent, now persists for 30 seconds instead of releasing faster, might hold a clue to the errant part. "Something" has got to have that specific capability.

The question is, can this happen only 0.x% of the time? Given the infrequency, why is the sensor more likely to be sending a rare bad signal than the computer mis-reading a good one? The latency of the sticking in year 15 does suggest mechanical origins. Is the sensor mechanical?

Much appreciated, Martin.
Rey
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