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Discussion Starter · #1 ·
Alright, so last weekend I put about 150 miles on the Volvo and she ran ok for her age. Go to start her today and she idles ok until I apply the brake. When I do she struggles hard to run and will stall unless I let up off the brake pedal. I can also hear what sounds like air leaking when I apply the brake, from under the dash it seems. I checked my vacuum lines with a propane torch and no change in idle so I'm not sure exactly what the issue is. Could I have a faulty brake booster?
 

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Absolutely yes.
 

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The D jet on the 142E is a speed x manifold pressure based FI system. Any leak that admits air to the intake manifold looks like a partially open throttle plate to the D jet and as a result the idle speed will increase. Any air leak through the booster should result in elevated idle speed. If you have a sustained air leak through the booster and you adjusted the idle speed down to compensate for the sustained air leak, then when you press down on the brake pedal and close off that little orifice in the booster which results in the pressure differential across the booster diaphragm, this may be blocking off the air leak reducing the air supply into the manifold and dropping the idle speed to the point where the engine won't run.

If you own or have access to one of those held hand vacuum pumps (minivacs), connect it up to the brake booster and see if you can draw a vacuum. It may take a bit of pumping because of the small size of the minivac. No vacuum indicates a leak. The other way to test this is to clamp off the hose from the booster to the intake manifold. If the engine speed drops, then the booster is leaking air into the intake manifold.
 

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Discussion Starter · #4 · (Edited)
I cannot say if the previous owner made such adjustments to the idle speed. I can say that up until now she has idled fine (ok, a bit rough but she needs a tune up, etc) and still does to a certain extent as long as I don't apply the brakes. I did notice that she does raise idle when I do introduce a vacuum leak.

As to the brake booster test. When I disconnect the vacuum hose from the booster and plug it the idle drops, plug it back up and the idle raises slightly.

The D jet on the 142E is a speed x manifold pressure based FI system. Any leak that admits air to the intake manifold looks like a partially open throttle plate to the D jet and as a result the idle speed will increase. Any air leak through the booster should result in elevated idle speed. If you have a sustained air leak through the booster and you adjusted the idle speed down to compensate for the sustained air leak, then when you press down on the brake pedal and close off that little orifice in the booster which results in the pressure differential across the booster diaphragm, this may be blocking off the air leak reducing the air supply into the manifold and dropping the idle speed to the point where the engine won't run.

If you own or have access to one of those held hand vacuum pumps (minivacs), connect it up to the brake booster and see if you can draw a vacuum. It may take a bit of pumping because of the small size of the minivac. No vacuum indicates a leak. The other way to test this is to clamp off the hose from the booster to the intake manifold. If the engine speed drops, then the booster is leaking air into the intake manifold.
 

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As to the brake booster test. When I disconnect the vacuum hose from the booster and plug it the idle drops, plug it back up and the idle raises slightly.
I think that this confirms that your brake booster is leaking air into the manifold. You could do a temporary fix for the engine dying when you hit the brakes by setting the idle speed with the line to the brake booster plugged / clamped. This will give you a pretty high idle speed under normal conditions; but, should prevent the engine from dying when you hit the brakes. Ultimately, you will have to replace the booster. I also have a 1971 142E and had to deal with booster replacement (due to complete lack of any servo assist). The booster on my car was part # 1387640 and at the time (15 months ago), VP Autoparts had the best price on the replacement part.

Check the part # carefully because there seems to be a couple of different boosters that ended up on the 1971 140s.
 

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Discussion Starter · #6 ·
Ok, went ahead and adjusted the idle (under the accordion looking intake hose) and it now feel less likely to die when I apply brakes. I checked out the part on VP but have a question. When you said to check the part # did you mean to compare it to a number that should be on my old booster or against something else?

I think that this confirms that your brake booster is leaking air into the manifold. You could do a temporary fix for the engine dying when you hit the brakes by setting the idle speed with the line to the brake booster plugged / clamped. This will give you a pretty high idle speed under normal conditions; but, should prevent the engine from dying when you hit the brakes. Ultimately, you will have to replace the booster. I also have a 1971 142E and had to deal with booster replacement (due to complete lack of any servo assist). The booster on my car was part # 1387640 and at the time (15 months ago), VP Autoparts had the best price on the replacement part.

Check the part # carefully because there seems to be a couple of different boosters that ended up on the 1971 140s.
 

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According to the parts manual, the 142 got booster part # 676256 up to chassis number ending in 178959 and all chassis from 178690 onward got part # 1212405. If you check out the first photo in post #15 in this thread:

http://forums.swedespeed.com/showthread.php?201780-What!-Another-142-Project-Car

you can see what the original 1212405 booster looks like in my car. I can't remember whether the part # was stamped on the booster. It might be worthwhile to see if it is; however, if your chassis # is after 178959, you likely have the 1212405 booster. From what I was able to determine, the 1212405 booster is no longer in production and has been replaced with the 1387640 part number. I don't know whether 1387640 is also a suitable replacement for the 676256 booster.

If you go to post #110 in the above thread, the first photo shows what the replacement 1387640 booster looks like. It is pretty much a drop in replacement for the 1212405 booster. The primary difference is that on the original booster the check valve is located at 12:00 o'clock on the booster body and the 1387640 booster has the check valve located about 60 deg clockwise so the original vacuum line from the intake manifold may be too short. An additional 'field spotting' guide is that (based upon the parts manual drawing) the earlier 676256 booster seems to have the check valve located about 20 deg counter- clockwise from the 12:00 o'clock position.
 
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