low boost, ?? about TPS resistance values

Kenneth Keith auditude at gmail.com
Fri Jun 3 13:15:55 EDT 2005


My 200q20v has been having giving me only 10psi instead of the
previously demonstrated 14.7psi on the same setup.  I just chased down
some vacuum hose leaks and got to drive it around on full boost for a
bit before the weather got hot (90-112f) and performance somewhat
expectedly went down.

I thought it was the ecu backing off boost due to the outside temp,
but it doesn't get over 10psi even in the cooler mornings.  It seemed
to point to the TPS, since just before it got the point it is now,
part throttle gave more power than full throttle, as if the WOT
section of the TPS was wore out or something.

I tested the TPS on the car, and another one I have.  I got 2600 ohms
on one, and 2800 ohms on the other.  Bentley says that the value
should be a maximum of 3600 ohms (from memory), but doesn't clearly
state what the minimum value should be at WOT.

My thinking is that if the TPS increases in resistance as the throttle
is opened, and it isn't increasing the resistance high enough, that my
ecu would not detect WOT and therefore not try to produce the previous
14.7 psi that is mapped for WOT.

So, does anyone know if a value of 2600-2800 ohms is typical for a
TPS, across terminals 2 and 3?

I had two friends test their TPS' that were not known defective and
they got similar values of 2500 ohms and 2900 ohms, IIRC.

I don't hear any leaks and don't yet have a setup to pressurize the
intake after the turbo.  If I had a leak, would it max out at 10psi
like that?  It is so consistent that it seems like it's related to the
boost control system.  I have the stock WG spring in place, but I
think 10psi indicates some assistance by the WGFV, which I have
replaced not long ago.

I have yet to run the output tests, but I look forward to doing that
and confirming that my somewhat recently replaced WGFV is still
working.  I suppose I could check the intercooler o-ring too, but it's
not acting like a leak as far as I know.  I have Samcos at all
pressurized joints, and the stock bypass valve passed the vacuum test.

I haven't seen the check engine light come on, and have yet to pull
codes.  Actually, I installed a momentary contact switch for pulling
codes, and it doesn't seem to be working correctly.  I need to dig
into that as well.  I'm mostly curious about the TPS resistance value
question, in case anyone happens to know.



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