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idle change when braking vacuum cant find the problem


blue65vw

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Do you have power brakes? Power brakes use the vacuum from the engine. The vacuum booster (the big canister behind the brake master cylinder) might have a leak somewhere. Hate to say it but you might have to replace it and unfortunately you have to replace the master cylinder also as that's the only way they are sold.

If you can get your hands on a vacuum gauge attaching it to the intake manifold can give you some answers. I think it would be normal for the vacuum to change when the peddle is first pressed but should return to normal right away. If it does not return then that is a bad sign. Normal vacuum at idle I think is 19 to 22 inches but I might be wrong on those numbers. Vacuum gauges can be used for other engine diagnosis also so it is a good tool to have.

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