Hi All,

After much testing and head scratching, I continue to be stumped by
this vexing problem on my 90 syncro. It is getting much worse
(frequent) but the engine always works fine until warmed up (enters
closed loop?).

Symptoms: Starts and runs fine until warmed up and then comes a sudden
loss of power, bucking, and sometimes dies when clutch is in.
Restarting used to cure the problem for a while, but no longer does.
Unplugging the O2 sensor cured the problem for 200 miles, but no longer
does. Holding the throttle above idle produces on-off surging from 2000
rpm to 4000 rpm. Will not stay at any given rpm except idle. If temp
sensor is unplugged, idle goes up and rpm's rise normally when upping
the throttle.

Here's what I've done so far:

Tested the following components with a good digital meter:
AFM-OK before and after cleaning with electronic cleaner, re-tracking
wiper arm, installing capacitor (no effect)
temp sensor-OK, but engine runs fine when unplugged, although with a
fast idle
ECU contacts/wiring-OK
O2 sensor-OK (new)
throttle valve switch-OK but I do not have a feeler gauge that small to
check the gap
idle stabilizer-vibrates
timing-OK, changing to either more adv or ret only makes the engine run
worse

Swapped these parts out of a working vanagon:
AFM- no change!!!
ECU-no change!!!

The following parts were checked, adjusted, cleaned as necessary:
distrib. cap & rotor (new 15k mi. ago), cleaned carbon deposits
  plugs (new 15k mi. ago) regapped and cleaned
ignition wires (new 15k mi. ago) appear OK
grounds to engine, tranny, ECU, etc .appear OK
Vac hoses show no obvious leaks using LP gas, visual, but have not
tested with meter

Not yet fully tested:
Fuel pump (original? no records from PO) makes normal buzzing
Fuel pump relay
Fuel pressure reg
injectors
PS pressure switch
Idle stabilizer control unit
control supply relay
Some vac lines and the vac tank
Fuel filter (new 15k mi. ago)

Any thoughts, ideas, shoulders to cry on?

Thanks

Keith Ovregaard
84 Westy "Brownie" Solar Charged Camper FOR SALE!
90 Westy Syncro