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The fact that pulling the fuse to the APC makes no difference says that the APC is not doing its job of increasing the boost level when you need it. Base boost is set mechanically and the APC is there to provide higher-than-base boost.
There are many possible causes. The APC relies on sensors and switches to tell it when it's OK to raise the boost and also on the boost control solenoid valve to raise the boost.
I believe there is a Frequently-asked Questions section on this site about base-boost troubleshooting. However, here are some suggestions:
1. Vaccuum line broken, cracked or disconnected. These are the thin black rubber pipes running around the engine.
2. Boost control solenoid valve not working or disconnected (or broken wire to it). This is on top of the radiator and has three rubber hoses coming from it. Best way to check is to borrow a known good one one (they are a bit pricey) and see if that fixes it. Be careful not to get the hoses mixed up, though.
3. Clutch or brake pedal switches not working. Above the clutch pedal (if a manual) and brake pedal are two switches - one for each pedal. These are connected to the APC and tell it when you press either pedal. The APC will not supply boost if either pedal is pressed. Often, these switches go out of adjustment and the APC thinks the pedal is pressed all the time. They can be adjusted.
Note that the brake pedal switch I mention is not the one that works the brake lights, so don't assume all is OK if the brake lights work. On a left-hand drive car (which I am assuming yours is), both switches will be above the brake pedal. On my UK-spec car, the brake light switch is on the left, while the pedal switch is on the pedal (on the right).
Try lifting the pedal (pedals, if it's a manual) with your left foot while driving to see whether the boost comes back. If not, this doesn't mean the switches aren't faulty, it's just inconclusive.
Can't think of anything else at the moment.
posted by 161.71.171...
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