My suggestion is the two relays - fuel pump and  current supply relay.  Bentley 24.48.  I've replaced both relays twice in my 12 years of ownership on my '90 Westy.   First occurence was probably around '96 on a tri  Experience was van would run fine and then just stop as if not getting any fuel.   Wait awhile and then it would run fine for a while.  Not much rhyme or reason.  Bought two of the relays(along with a spare fuel pump & filter) after changing the relays NO PROBLEMS.  Then about a year and a half ago the engine began to just start stalling while driving for a second or two and then start again while on the freeway.  At stop lights a couple of times it would cut out but then restart OK.  Again I changed the two relays (they are cheap about $7.00 I think)  again NO PROBLEMS.  In my '90 it seems thatthose relays have a life of about 6-8 years.  I just keep a pair in the van.

Russ

> 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