Engine stalling when brakes applied. Faulty brake booster?
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    1. #1

      Engine stalling when brakes applied. Faulty brake booster?

      I have a '93 Volvo 240 Wagon. 145K miles.

      This issue started earlier this winter. When I start the car up, if I press the brake pedal with a medium/firm foot, the engine rpms will fall and jump. If I take my foot off the brake pedal or just barely touch the brake pedal, the idle smooths out. After the car fully warms up this becomes less of an issue.

      I do hear a rattling/patter/putting sound from under the dash when the car is cold. It goes away or fluctuates when I apply the brakes.

      When I step on the brake pedal with firmness, I hear a whooping (air escaping) sound from under the dash.

      The brakes perform very well. I don't feel any loss of braking power.

      After the engine is off and the car sits for a few hours, the pedal is very firm until I turn the engine back on.

      I've replaced the vacuum valve on the front of the brake booster.
      I've replaced the vacuum line on the front of the brake booster going to the intake manifold.
      I don't have any other leaks.
      I've checked/swapped both my ICV and AMM.

      Do I have a faulty brake booster?

      Thanks,

      Mike

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    3. #2
      Senior Member
      Join Date
      Aug 2004
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      Temple, Texas, USA
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      Quote Originally Posted by mike.volvo.240 View Post
      I have a '93 Volvo 240 Wagon. 145K miles.

      This issue started earlier this winter. When I start the car up, if I press the brake pedal with a medium/firm foot, the engine rpms will fall and jump. If I take my foot off the brake pedal or just barely touch the brake pedal, the idle smooths out. After the car fully warms up this becomes less of an issue.

      I do hear a rattling/patter/putting sound from under the dash when the car is cold. It goes away or fluctuates when I apply the brakes.

      When I step on the brake pedal with firmness, I hear a whooping (air escaping) sound from under the dash.

      The brakes perform very well. I don't feel any loss of braking power.

      After the engine is off and the car sits for a few hours, the pedal is very firm until I turn the engine back on.

      I've replaced the vacuum valve on the front of the brake booster.
      I've replaced the vacuum line on the front of the brake booster going to the intake manifold.
      I don't have any other leaks.
      I've checked/swapped both my ICV and AMM.

      Do I have a faulty brake booster?

      Thanks,

      Mike
      Welcome to Swedespeed, Mike.

      If the brake fluid level is stable and you are positive of no vacuum leaks anywhere it is possible the booster has internal problems causing a rapid vacuum change which affects engine idle.

      Is the OBD clean?

      George Dill

    4. #3
      Hi George,

      Brake fluid level is constant. I'm fairly confident there aren't any other vacuum leaks. I've replaced all of the vacuum lines as well as intake manifold, TB, and injector seals/gaskets.

      No check engine lights.

      - Mike

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    6. #4
      Junior Member
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      Nov 2013
      Location
      Halifax, Nova Scotia, CA
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      I had a similar issue with my Ranger a few years back: I could hear a hissing sound from under the dash every time I pressed on the brake pedal. Like you, I didn't notice a loss in braking power, but without the MAF it didn't severely affect the engine speed.

      Turns out that the gasket around the plunger going into the brake booster from the pedal had degraded and crumbled. It was damn annoying, so my solution was to cap off the vacuum line going to the booster and to tough it out until finally salvaging another booster from an Aerostar.

      So I'd suggest getting under the dash and looking around with a flashlight (and maybe a mirror). Can you pinpoint the source of the air noise with your head in the foot well?

    7. #5
      Member
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      Mar 2008
      Location
      Sarsfield, ON
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      Quote Originally Posted by mike.volvo.240 View Post
      Hi George,

      Brake fluid level is constant. I'm fairly confident there aren't any other vacuum leaks. I've replaced all of the vacuum lines as well as intake manifold, TB, and injector seals/gaskets.

      No check engine lights.

      - Mike
      George's note means have you done all of the OBD1 tests: i.e codes (fuel/intake and ignition) and ECU input and output tests. I f you have a Bentley, go to 241-6 to 241-8 and 280-3 to 280-4. If you don't have Bentley, I strongly suggest you get one. In the mean time I'll try to find the tests somewhere in my bookmarks.
      '88 244 auto (parts car), '89 244 5 spd. (daily driver), '92 245 5 spd. (my car) '80 Holiday Rambler/Ford E350 (tow vehicle and track crash pad), '95 GMC K2500 (local hauler/back-up tow vehicle), '83 Mazda RX7 (race car when I have the funds), '99 Miska 20' car hauler.

      The man's prayer: "I'm a man, but I can change, ... if I have to, ... I guess."

    8. #6
      Member
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      Mar 2008
      Location
      Sarsfield, ON
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      3,126
      Quote Originally Posted by John2x240 View Post
      George's note means have you done all of the OBD1 tests: i.e codes (fuel/intake and ignition) and ECU input and output tests. I f you have a Bentley, go to 241-6 to 241-8 and 280-3 to 280-4. If you don't have Bentley, I strongly suggest you get one. In the mean time I'll try to find the tests somewhere in my bookmarks.
      OK, here's the on-line tests: http://www.swedishbricks.net/700900F...nostic%20Codes Although it's mainly for 700/900 cars, most of the 240 information is in there too.
      '88 244 auto (parts car), '89 244 5 spd. (daily driver), '92 245 5 spd. (my car) '80 Holiday Rambler/Ford E350 (tow vehicle and track crash pad), '95 GMC K2500 (local hauler/back-up tow vehicle), '83 Mazda RX7 (race car when I have the funds), '99 Miska 20' car hauler.

      The man's prayer: "I'm a man, but I can change, ... if I have to, ... I guess."

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