Check very carefully for vacuum leaks.

Check/adjust the idle switch at the throttle plate.

Put an oscilloscope on the signal from the Hall sensor at the distributor to
check that the pulses are regular and uniform.

Use an oscilloscope or digital voltmeter to watch the signal from the O2
sensor when the engine is warmed up.  If it doesn't bounce up and down very
well between one or two tenths of a volt and around nine tenths, it may
indicate that the mixture is wrong because of vacuum or exhaust leaks, etc.
(assuming the O2 sensor is OK)

HTH
Larry A.

On Jan 2, 2008 1:37 AM, Zoltan Kuthy <zolo@foxinternet.net> wrote:

> Hi guys,
> I hope, you all had a great New Year eve and slept well after.
> Now, back to the puzzle.
>
> I have a friend with a '87 Vanagon bus.  He says, he has changed almost
> everything; Temp II sensor, Oxygen sensor, computer, distributor, cap,
> rotor, cables, plugs, new injectors, AFM, ICU, idle control valve, cleaned
> all the grounds or put new connectors on, etc.
>
> Now, he says, the car is running shabby, and when he takes off any of the
> cables, the engine does not seem to change running any different.
> This guy is probably the best equipped mechanic in the country with all
> the imaginable testers and the best Snap-on everything you can dream of.  He
> works on Mercedes, BMW, Porsche, Audi, VW,
> But he loves to drive his Vanagon and this is the only car that gives him
> the most trouble of all, he says.
> He is totally baffled, confused and embarrassed.  He asked me if I would
> send this message to the list, in hope there is an idea he did not think of.
>  He is puzzled, shaking his head and can't believe it.
> But, he says, evey now and then the car coughs a little and then it runs
> great for awhile.
> I could not help him.
> Anyone?
> Many thanks for all the help I got from the Grand List so far.
> With the best regards,
> Zoltan
>