I posted this last week and took the advise of making sure that there were no vacumn leaks and reset the timing. I am still experiencing my Audi 400 1987 stalling out - It starts up ok but will stall out after I drive a couple 100 feet to the corner and take my foot off the gas to brake - even after I have driven about 40 miles and come to a stop at the end of the exit ramp and the rpm's drop from 2800 to idle it will stall out - any suggestions are appreciated

 

Without diving in too deep, I suggest you do a fuel pressure test. Also hook up a simple tune up vacuum gauge (~$20-$50) so as to get a rough idea as to what is going on.

How to read engine performance using a vacuum gauge.

After you stall out can you restart right away or do you have sit and wait from a few seconds to minutes?

Here are several things that I have seen cause idling problems.
1. Stuck open intake or exhaust valve(s)
2. Clogged air bypass port or dirty throttle
3. Throttle position Microswitch defective
4. Defective Auxiliary Valve
5. Wrong system fuel pressure
6. Wrong timing
7. Vacuum leak
8. Bad Hall Sensor in the distributor
9. Dirty air filter
10. Dirty fuel filter
11. Sticking Mass air flow sensor
12. Defective Engine Temperature Sensor
13. Low system voltage
14. Corroded electrical contacts

 

Thanks - I have my work cut out for this week - By the way, after it stalls - and it doesn't do it all the time, it does start right up - If I am rolling when it stalls Ijust re engage the clutch and it pops over

 

Two more things I forgot to add was:
15 Injector seal(s)
16 Bad injector(s)

If it doesn't stall all the time and you manage to restart then I would say that it eliminates the "hall sensor." A defective Hall sensor will cut out at any speed and often fails to restart. Is it safe to say that the problem is more intermittent? After restart does the car idle OK? Does it happen only when cold, hot, etc?

 

it never really smooths out to a level "purr" when at idle - almost sounds as though there is a miss - I drive 40 miles on the freeway, I set the cruise at 65mph and it just trucks down the interstate smooth as a kitten with the rpm's holding steady at 31k in 5th gear, but when I get to the stop sign at the end of the off ramp, ya never know if it will stay lit or not. When I exit the rpm's are at 3100 - let up on the gas it drops to about 26k - put in the clutch and it drops almost immediately to 200 and then bounces back up to 750 - 900 - if it doesn't stall first

 

Check the dashpot on the throttle a.k.a. deceleration valve. When you rapidly slam the butterfly valve this device slows it down and delays full throttle closing by a few seconds. The factory service manual has a section for adjusting and testing this device. The only other thing that might also cause such a problem is the fuel cutoff which is controlled by the ECU. The fuel cutoff is actuated by the closed throttle (idle position) microswitch and engine RPM's. If the switch is closed and the RPM's are above ~1500 the ECU applies current to the differential pressure regulator effectively cutting off the fuel to the injectors, reducing emissions and increasing mileage.

 

I had an '84 4k non quattro with a similar problem. It would stall at random times. Sometimes it would start right back up and others not. Sometimes it would also run like a loaded up two stroke dirt bike. It ended up being a sensor. I cant for the life of me remember which one. I think there were about three or four close to each other near the knock sensor and it was one of them. Not much help I know, keep us posted, and good luck.

 

this is all great information and gives me a path to start on - although I will change the two fuel filters and clean the throttle body first. If this maintenance doesn't improve things, I will move into the sensors etc.

Thanks again for all the info - Keep those ideas coming, will let you know how things develop

 

I think the mystery is solved - I did change both the primary and secondary fuel filters - what a challenge to get the fittings free without breaking the lines - actually I cut one line and replaced it with high pressure hose/clamps.

Even with the new filters, rotor, cap and plugs I had the same problem - I cleaned the throttle body and reset the timing - no improvememt.

I then spotted a split rubber elbow on the large rubber intake boot - I replaced it with an extra from my "spare engine" - yes I have a spare 1.8 in the shop. That seemed to solve the problem almost - still not running 100% so I kept looking for vacuum leaks and I found a small crack on the large rubber intake boot! When I put my thumb over the crack the rpm's went from 800 to 950+, a little electrical take and were cooking - looks like a trip to the salvage yard next saturday to find a better one - Audi probably wants $150 for a new one.

Thanks for the help and suggestions

 

The intake bellows that runs from the mass air flow sensor to the intake manifold is a common and often overlooked part. Often I hear these have a tendency to crack on the side that you can’t easily see. You might want to check and replace the engine and transmission mounts. If the engine is rocking and pitching too much you will have a repeat.