Old Library

just going thru the VR6 service training manual,( just got it)
I noticed something interesting.
First those who have recently experienced this, are your
cars 98's and newer?
(95's we know can be the vacuum lines to the fuel pressure reg)
I noticed that one of the things changed in 98 on up was the
carbon canister frequency valve. this is the little valve
that clicks away on the pass shock tower right next to the
airbox kinda under the air mass sensor.
I have a 96.5 with the old style valve and never have an
idle problem. if its the newer cars could this be a culprit.

According to the manual " If power to the valve is
interrupted, the valve remains completely open. This could
lead to rough running at idle speed and during load acceleration."
The ecu can detect if there is an open or short. thats only
electrical. there could still be mechanical failure not
detected by the ECU.
Note also in a normal state when the engine is started it is
closed as well as when the motor is not running. under
"load" the valve is open at full throttle and completely
closed  during deceleration fuel shut off. maybe this also
has an effect on that 2nd gear " stumble ".
Just a coincidence to note on the change of that part in
conjunction with the newer cars having an idle problem.
The stumble effect is on all cars and could be a response
time to the valve in sync with the drivers right foot when
shifting.
Just points to ponder!
Doug
SPEED

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