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car shakes when stopped at light and brake is held please help

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Project98GT

New member
Ok here is what I have been trying to figure out for some time now. When I'm driving and I come up to a stop light/sign and stop my car shakes just while the brake is held. Here are some of the things I have done to try to get rid of this problem. I changed the plugs, wires, LIM, UIM, new air filter, looked at the vacuum lines and fixed the one's that looked like they could be leaking. And the problem is still there so I would like some help with trying to fix this problem. I don't know if this could have anything to do with this or not but some times my tranny shifts hard and sometimes it doesn't. Any help with this would be grateful.
 


year, make, model, engine, miles, mods and so on please.

does sound like a vac leak.

get some carb cleaner and spray the vac lines while the car is idling, if the idle jumps up while spraying the lines, the last place you sprayed is leaking.

spray any sensors the vac lines lead to as well.

hows your tranny fluid level? and color of fluid?
 
my intrigue did the same thing. I never did figure out what it was. If its the same shake that I'm thinking of it felt like worn engine mounts or something similar. maybe drive shafts were sloppy I don't know. Can you feel it through the steering wheel? Mine did. Outter tie rods were changed and inners were still tight. I changed the torque strut mounts and the passenger side drive axle with no difference.
 
its a 1998 Grand Prix GT with around 265k or so. Im not 100% on the mileage due to the previous owner changed out the odometer. Some one on here ran my vin and found out it had like 250k ish like a year ago. I can feel it in the steering wheel I should of said its like a shave/vibration. I just changed my tranny fluid in the past 9 months and a axle seal due to it leaking. Ill try the carb cleaner on the vac lines to see if I messed a leak.
 


if your upstream O2 sensor has more than 50k on it replace it.

the O2 is a "trusted" sensor, if it gets old/damaged/skewed it throws everything off...

the other thing is that these idle rough just from the inherent design
 
Do the rpm's fluctuate while this happens, or do they stay pretty stable? If they aren't fluctuating, it's probably just a motor or transmission mount.
 


Just saw this thread, and my 2001 GP is doing something similar. At a stop, in drive, i can feel the engine vibrations in the floor. idles ok, shifts ok. going to check all mounts.
 
Sorry, to me this screams a leak in the brake booster vaccum line. If he's having more trouble specifically at a light when the peddle is depressed, I would check or just go ahead and replace the vaccum line at the brake booster and the check valve too. Either of those should be checked and with mileage should just be replaced outright.
 


hey, on our 2007 GP, i've had this problem since we got the car second hand, lately its been worse, and no one else seems to really notice it. It vibrates the interior now and I've always noticed, by looking at a scanner, a ~100rpm drop when the brake is pressed. I thought maybe voltage, alternator, as its cyclical vibration. I do remember looking at the brake booster hose as suggested, you think just changing it and seeing if it would work is a good idea? I have noticed more thumps in shifting, I guess mounts too?
 
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