Steve_B

My MY97 has developed an intermittant fault resulting in the operation of the boost control solenoid when the vehicle is at idle, it also seems to effect the rate of RPM decay when changing gear - the revs hold for a second or so before decaying when the fault is present. (it does not appear to be air temperature related, happening equally in the warmth of the summer and on these cooler days).

It is however reset when a new driving cycle is initiated. (if the fault is present, switching off and then restarting removes the problem)

The dealer has had the car on several occasions but has said "No-Fault-Found", I have even driven it down there when the fault is present and connected it to the SELECT , and everything is said to be "Normal" by the techy.

I want to know what sensors other than those required to read the boost map (load, RPM) apply trims to the boost map values.
i.e. knock, MAF, throttle position sensor (TPS).

AlexM

I maybe about to say something dumb, but I thought the boost solenoid always pulsed at idle?.

Maybe if it only does intermittently, then the solenoid IS faulty. Has your dealer tried substituting it for a new one?.

Rgds,

Alex

Bob Rawle

Boost solenoid starts to pulse as soon as the throttle opens, at idle its not pulsed. Don't think that your problems are related to the boost, map sensor only controls boost unless the car knocks badly and then the ecu reduces boost for safety. Sounds as though you may have a throttle position sensor fault or the ecu is just playing up.

Steve_B

Alex, i doubt it is the solenoid, it is obviously told to come on by some other ECU input...

Bob .. Yes I agree that the solenoid is normally disable at idle by the throttle position sensor.

You mention that the boost may be reduced due to a nock condition being detected, do you think that a correction would be applied to the whole of the boost map or selectively ?
If is is applied to the whole of the map surely the TPS at idle would overide any correction !

Bob Rawle

The knock condition will definately not affect idle ... just making the point that there a only limited influences on boost.

Bob