1990 200 TQA..ISV WOT WGFV.. When and why

[Nate Stuart]

Quoting Nicholas  Lawrence <nick at beol.net>:

>     I suspect my ISV is sticking, I've tried cleaning numerous times to
> no
> avail. Idle is erratic high and will go down if I unplug ISV.

Then why is it sticking? If it were sticking wouldn't you expect the idle to 
stay high no matter what the electrical input?

>     Question:  when does the ISV work and why not leave it unplugged?
> runs
> OK in that mode.

Go ahead, you can leave it unplugged if you want. Just don't expect the car to 
idle too well in the colder weather, or when the AC comes on. I'd check your 
idle switch to ensure that it is making a good solid connection. Also check you 
WGFV vac/boost routing that you mentioned below. Could lead to a small vac 
leak, I suppose. Can't recall what was causing this same symptom on my 5ktq at 
the moment... If I do I'll get back to ya.

>     The WOT is open at full throttle (no continuity) and as I understand
> it
> has to function in order for boost to be controlled by ECU. 

It tells the ECU what to do with the boost map, as well as fuel enrichment.

> With analog
> gauge I get only 4psi and bypassing the WGFV brings 12 plus and fuel cut
> off
> so it is capable of boost.

What do you mean by bypassing? Applying straight manifold pressure to the top 
of the WG?!

>     Question:  Is there a reason for not "making" the switch full time
> and
> letting the ECU handle boost?

How do you think the ECU handles the boost?? It uses the WGFV! Sounds like your 
boost/ambient lines are reversed. Try swapping the two lines that don't go into 
the WG cap and see what happens.

Audi does have a habit of putting most of these parts on the cars for a reason 
ya know!? :-)

-Nate
'89 90q
'87 5ktq (donor)