Date:         Mon, 6 Jun 94 10:40:40 CDT
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         smitht@jupiter.sun.csd.unb.ca (Tim Smith)
Subject:      Re: engine surge at 1100rpm

>  i am still battling an engine surge 1100-2000 back and forth in my
>'85. it doesnt fit the pattern of the one for which the auxiliary wiring
>

This problem happened to me when my '85 vanagon was still under warranty, VW 
couuldn't fix it either. It turned out not to be one component of the FI 
ssystem, but three. The idle sensor was out to lunch, the O2 sensor 
likewise, and the airbox (throttle flap). The regular repair  procedures are 
to pull each
component, replace it with a KNOWN good one, then try again. This won't work 
if more than one component is causing the problem. VW replaced these and the 
 main FCU on my van etc. etc. individually, and eventually told me 'all vans 
drive like this, get out'. this after a six month period, during which my 
van spent 27
days in their shop! The FCU has default settings if you disconnect the O2 
sensor, but it can't  correct for a deranged one, so pull the lead to 
isolate that component, then swap the idle stabilizer for a fresh unit. 
DON'T TAMPER with the airbox settings, a small screw  hidden under a blue 
cap on top of the box. This is a factory calibration unique to the airbox, 
not to your car! Make sure the flap moves freely, any backfires can damage 
this by driving the flap against the stops. You can verify the electrical 
resistance reading on the flap as it moves, they should change smoothly as 
it is moved. Check the idle switch, near the throttle body/cable. Bently 
manuual is very useful, and $$.
Be prepared to spend some time on this. You need to try components when the 
engine is completely cold and then throughout the  warmup/ normal region. 
Dying electronics are more temperature sensitive than normal (or dead) ones, 
and elusive to track down. 
My surging deteriorated to no power off idle, I had to rev high, slip the 
clutch to get moving. If it started to die even then, it was terminal, coast 
to the roadside, turn it off, wait a minute, restart and repeat. Didn't work 
well in the big city! Eventually it would die while in motion, 45mph 3rd 
gear, a real blast when heading up a freeway on ramp. good luck, tjs