[200q20v] Throttle Switch/Potentionmeter failure and High Boost

C1J1Miller at aol.com C1J1Miller at aol.com
Fri Nov 17 10:11:21 EST 2000

In a message dated Fri, 17 Nov 2000 10:03:55 AM Eastern Standard Time, 
"Forhan, Thomas" <Thomas.Forhan at mail.house.gov> writes:

<< Thanks Chris, I'll look at peeling back the boot Saturday and redo Scotts
voltage test, and recheck the breather and control valve.

Re the high boost indications, I got the car with an unknown chip already
installed. No indications on the outside of the ECU.  Of the two prior
owners, one denied doing anything to the car, the other did not respond to

Because the in-dash guage can read 2.4, my presumption is that this is a
replacement instrument. Seems like a chipping that paid attention to
details, so I might presume they included a higher rated pressure transducer
as well.

With the failure, for whatever reason, of the potentiometer, max boost is
indicated is 1.9 bar. The Bentley says with a pot failure the wastegate
spring serves as a mechanical default.  Does the 1.9 imply that the
wastegate spring was replaced as well?


Tom F.

Tom, it could be a replacement computer from a '92 S4 (that reads to 2.5 
bar), assuming our ECU could output the correct info, and assuming it was 
properly rescaled.

I assume engine off shows 1.0 bar on the computer?  Perhaps the computer 
reads higher than actual boost.  Only way to tell is to install an analog 
boost gauge and see what you're really seeing for boost.  A nice gauge is 
around $40; best is one showing boost to 25psi, plus vacuum; however, 
remember that they are still not adjusted for altitude (unless you get a 
fancy and expensive airplane gauge, for example).  At sea level or 
thereabouts, they're accurate, though.

If the wastegate frequency valve doesn't work or is unplugged, you get boost 
based on the spring tension minus intake manifold boost pressure.  Stock, 
that's about 1.4 bar; stiffer spring would get up to around 1.8 or so.

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