74 Bus w/ 78 FI stalls at idle when warm

There may be two separate problems: the idle and the jerking.

Concentrating on the idle, my inclination is that there is a small vacuum leak. The aux air valve may be compensating for this until it decides that the engine has warmed up.

You might try this: Adjust idle up (or put brick on pedal) so that the thing will idle at some speed after warmup. Then go around to every stinking hose and fitting with a solvent spray. Any change in RPM will show up a leak. Don't overlook the Decel valve in this.

Less likely, but worth checking, is fuel pressure. Put a 60 psi gauge on the fuel ring tap and see if the regulator is functioning per the book.

I don't see anything that suggests a dbl relay failure.

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Speedy Jim

Clearly either fuel pressure or a vacuum leak....my 80 Vanagon has relatively the same motor....and the 02 sensor corrects mixture from the fuel injection, but on yours, I assume you are carb running

Defenetly vacuum leak. same exact simptoms on my bug. probably the same problem/solution.

Distributor ignition advance components? Sticking shaft for the mechanical advance or sticking plate for the vacuum advance or a bad vacuum advance unit. Weak spark from the ign. coil? Bad or non-Bosch Ignition Rotor?

How is the idle when the engine is cold? Higher than normal? If you increase the warm idle how does that affect the cold idle?

Maybe it is running too rich when the throttle closes and the engine is flooding out? How did you adjust the CO with the Air Flow Box? Is the flap inside the AF Box sticking?

A large vacuum leak should be hissing at you, and a little carb cleaner sprayed here and there should help locate any small ones! ;-) Don't forget about the FI seals too!

Just throwing out some ideas but I know very little about the FI on the Busses. In article

Thanks for the replies.

OK, I checked and found a (small) vacuum leak near the decel valve, which I repaired. Took it out on a test drive, and I still got the same problem. It ran absolutely beautifully, and then POW -- stall when coming to a red light. I kept driving a bit more, and then the crap really hit the fan. Cruising along at 55 MPH, suddenly the engine started losing RPMs, even with the throttle open. I had to keep downshifting to keep the engine alive, until it finally stalled out.

Of course, the starter solenoid (which has been going bad) chose this exact moment to give up. I was able to compression start it sometime later, and it did start up again.

Does this sound like it could be an ignition/coil problem? The weird thing is that it stalls when warm, but doesn't ALWAYS stall when warm. The points and rotor looked OK last time I looked at them. Neither are worn or pitted and the dwell is spot on.

When it rains, it pours.

I have had that symptom on a brand x with a bad coil

MD

I had similar symptoms with another brand of car as well, turned out I got a load of gas that had a large amount of particulate matter that was plugging the pickup screen in the fuel tank. Car would run fine for a while, then lose power as the screen got plugged and the fuel flow dwindled. Stop the car for a while, the junk fell off the screen, and it would run fine until it plugged again.

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I know that you said you replaced the #3 temperature sensor, but I would double-check that to make sure that you have a REALLY good connection. It may also be possible that you have a defective sensor.

The reason I'm saying this is that on my previous 1979 Bus I had exactly these same symptoms and that temperature sensor was the problem. The symptoms would start with a little high-speed hesitation, followed by bucking, then nearly total loss of power, and finally the inability to keep the engine alive. When the sensor was replaced, the problem went away and never returned.

--- Robert Winters