A bit crazy sometimes

[nine-fiver]

Some advice required please. Her '0-2 9-5 has developed a gremlin that needs investigation.

It goes like this. Every now and then it goes a bit psycho and boost levels are too high too quick. Suddenly the car feels like the sport button has been pressed and the front wheels scramble to bite the bitumen. Way too much power and fuel consumption jumps a lot. The temp gauge has been lower than usual lately and the air con then switches itself off because of it. I think these are related to some degree, as this is also intermittent. It has cut out in traffic a few times, but always restarts as if nothing has happened.
I replaced the CPS as it was a bit out of range, and that has made hot restarts better, but not great.

Suggestions most welcome...

[Steve440]

Throttle body?

If its not under proper control of the ECU it can do odd things.

Steve

[nine-fiver]

Give it a proper clean? It has been a while since I last did it.

[ScarbSaab]

Boost pressure control valve? I'm not sure how it is set up, but even if it is designed to fail dumping all boost it might just be sticking, so the dump valve doesn't operate.

[nine-fiver]

Would that explain the madness under acceleration?

[ScarbSaab]

Would that explain the madness under acceleration?

Presume you are asking about my suggestion? If it is not limiting the boost, then it could overboost (though I think it should throw a CEL if that happens) which might give it more than intended power. I recall someone else having a similar temporary issue when they came off a roundabout onto a dual carriageway, accelerated and it tried to shred the tyres. But it's purely a guess. I've no idea what effect the unregulated boost would have. I'm guessing it might behave like a lunatic chipped car.

[nine-fiver]

The car is 'hooting' every now and then. I will put on another unit shortly. 

[Audax]

hooting is a sign of the dump valve failing.

[nine-fiver]

Would that explain the boosting issue?

[Audax]

It could maybe explain the boosting issue but the failure mode is to lower boost although if something odd was happening maybe the car attempts to overcompensate. Given the ease of testing a dump valve (check it springs open/shut, isn't split etc.) and checking the vacuum hoses I'd do that as first step. Other possibility is that you have 2 problems related to boost at the same time if so fixing one will make finding the other easier so again, given the ease of checking this even though it doesn't really match the symptoms makes it an obvious thing to do.