'94 (L) Volvo 940 turbo estate, 140K miles, cut out 9-10 times in the last few journeys, generally at low speeds and on braking. All dash lights come on, brakes and steering are almost lost but as it has always been at low speed I've been able to halt fairly safely and it restarts immediately. No relation to engine temperature, fuel level, weather, length of journey. All fluid levels seem ok, always uses a lot of oil and there's a small patch of oil underneath when it's parked, front brakes do need attention. Have had a fuel pump relay go on an older 740 but that wasn't related to braking. Daughter's VW Polo has a stepper motor/idle control fault, but that is constant and this is very intermittent. Any ideas would be appreciated.

http://www.brickboard.com/FAQ/700-900/EnginePerformanceSymptoms.htm#CarStallsWhenBrakesAppliedVacuumLeakorFIRelay

Please check the vacuum control valve close to the brake booster unit
Kind regards,
John

Thanks all for advice, now the holidays are over I'll get the car booked in. One more query: when it does stall, I step on the brake to stop asap because the steering isn't responding and sometimes I've been braking on a curve. It's an auto box - I've been worrying more about getting the brakes to work than shifting the auto gears, but is leaving it in 'D' correct? Would immediately shifting to 'P' work if it's already stalled? Too scared each time to think about it.

If you're asking if you should use "Park" as a means to stop the car while in motion, the answer is absolutely not. That will damage the tranny, and likely won't stop you unless you're moving quite slowly.

jp
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'93 945 Turbo (201K miles), '93 945 (140K miles/I maintain for a family member), '93 945 Turbo (sold w 145K miles), '92 Mercedes 190E (174K miles), '85 Jeep CJ-7 w/ Fisher plow (225K miles), '53 Willys Overland w/ Fisher plow (sold to a loving home)

The server seems to be reacting slow; I got no response so I sent it again!

How about a problem with your brake vacuum booster, or check valve? If your booster isn't maintaining a reserve vacuum, hitting the brakes may be affecting your engine function.

Some checks:

1) After the car has been parked for a few minutes, press down on the brake pedal several times. Each press should give a slightly higher and harder pedal.

2) When successive presses result in the same pedal height/firmness, hold the pedal in the depressed position, and start the engine. The pedal should drop about an inch.

A failure of the above tests could be a check valve problem or the booster itself. Since engaging the brakes triggers your problem, I don't think it's the hose; a hose problem would affect engine function constantly, and without an airtight connection to the booster, wouldn't allow the booster to affect the engine).

When my booster failed, the problem only occurred when it was very cold. Apparently the diaphragm in the booster wasn't supple enough to form a proper seal.

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David Armstrong - '86 240(350k km?), '93 940T(270k km), '89 240(parts source for others) near Toronto

1] Idle Air Control Valve/Throttle Body cleaned lately? Throttle Position Sensor reset? Standard maintenance item along with breather box/lines cleaning.

2] Check the wire coming off the RPM sensor. Typical failure item over time. Insulation will break down and wire will start to fray. 10 minute R&R w/standard tools.

Look in the FAQ's for details about these items. I suspect it is one of them (leaning toward #1).
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Bob K