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740 rough idle (only when in gear and brake applied)

Volvo Thief

New member
Joined
Aug 3, 2006
Location
Garden City, Michigan
I have a persistant rough idle. Its only when I'm at a light stopped and in gear. In neutral its fine and while normal driving its fine. I've replaced the knock sensor but the problem persists. Could this be fuel delivery related or a vacume leak somewhere? What things can I check? This is a non regina car.
 
Check the brake booster. Plug the vacuum line to the brake booster, start the car, apply brakes and check for rough idle. Sounds like your brake booster is leaking vacuum.
 
First step is to make sure your throttle body and idle motors are clean and adjusted properly. :)
 
Does the RPM drop?

The RPM's do not drop much if at all. The engine just gets terribly violent and shakes and rattles the whole inside of the car! This has been going on since I got the car 2 years ago, It happens when its cold, when its warm, when it rains, when it snows, and when its hot. So pretty much all the time. But only when in gear and brake applied. Best example would be as I said at a traffic light. Still runs great otherwise :) I'm just now finally fed up with it.

In the meantime I will check the brake booster and throttle body.
 
Most likely vacuum leak having to do with the brakes.

Might be something electrical too, disconnect the brake light switch wire at the pedal to verify that.
 
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