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Thread: Bucking/jerking at freeway speeds

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  1. #1

    Bucking/jerking at freeway speeds

    Okay so I bought this car (01 4 cyl soc es model) The car has 200,400 miles when I got it 300 miles ago it vibrated like crazy, I know now that this is because it has bad engine mounts, but before I knew that I read it could be a variety of issues. So I started by changing the spark plugs, the car still had the vibrations, so I moved to the next easiest/cheapest thing which was cleaning the IAC valve and throttle body, and this is where the hell started.

    I cleaned the IAC and put it back in, naking sure all the solvent was dried. I started the car and it ran fine. The next day I went to start the car and it wouldn't run unless my foot was on the gas, so I looked up the issue and somebody somewhere said the idle set screw needed to be adjusted, so I unplugged the iac and set the screw to where the idle was around 900 rpm. It ran fine after that, but sometimes it idles high and sometimes it idles low, but it always runs.

    There is however a recent developement that seems more serious. When I get the car on the highway at 65 mph it starts bucking/jerking randomly. there is no change in engine rpm when this occurs. it happens with cruise control on or off. the transmission shifts smoothly in every gear. and at low cruising speed the buck does not occur. I'm wondering if a idle set screw set wrongly could cause this issue? Or maybe there is a bad wheel bearing? Can a wheel bearing cause a bucking sensation?

    I've checked thoroughly for a vacuum leak as well and have had a mechanic friend check with his equipment.

  2. #2
    Update: I've been trying to diagnose the problem further, and so I put it in neutral with the parking brake on. I revved the car slowly up and found something odd. The "bucking" is a surge that only happens between 2.5k and 3k rpm. 2.5k, no surge, 3.2k, no surge, anywhere between and I get a massive surge.

    Could this be the EGR valve? Could it still be the IAC or idle set screw? Camshaft sensor? I'm at a loss.

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