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Q: I have a rough idling problem and when I apply the brakes, it shakes. What's up? on 1994 Chevrolet Caprice

On cold starts, the car is fine in the idleing, or park position, but when I drive it before letting it heat up there is a knocking/grinding noise coming from the rear of the car. The more I drive it, it stops but then I start having shakeing when applying the brakes and rough idling.
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Diagnosing the rough idle when warm from an armchair is hard. I can tell you that you have (at least) 2 seperate problems. Rough idling when hot is engine related, and grinding/shaking in the body during braking are not connected. Where does it shake when you apply the brakes? Front end wobble or like the whole vehicle vibrates? To figure out if it is front or rear brakes, apply the brake pedal at about 45 mph and see if you notice the steering wheel shake/move side to side. If it is front end wobble, you should have the rotors checked for runout, the wheel bearings repacked and the steering and front suspension checked for slop/play. If the wheel does not shake and or move, but you feel it in the "seat of your pants", then try applying the parking brake (carefully) at 40-45 mph without touching the brake pedal. To do this, keep the park brake release handle pulled out and push reasonably hard on the park brake pedal with your foot to apply them. If it is in the rear brakes, the vibration will be there without the front brakes applied. If it's rear, have the drums checked for out-of-round problems, and the rear shoes and hardware checked for wear and or loose/missing hardware. May also have a rear differential issue.
Thanks for your reply! The whole vehicle vibrates. The brakes aren't the issue, I believe I need to have a tune-up, which is way over due, and then check back to see if any of those problems have been fixed. I just had service done, I believe they changed out the ignition coil and ignition module and the car starts fine. But the shakeing still happens. After the tune-up I'll see what happens next. Sounds like it could be a number of things. Much appreciated. I know nothing about cars so anything helps.
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