Hard shuddering at above 65 when easing off the throttle.

[Shimmy]

Hey there, I'm new to the forums so there may be a thread already and I'll look but I figured I'd start by posting a thread. I recently had my timing and serpentine belts replaced on my 2000 es 2.4 as well as my exhaust patched. After that it seemed like it was running great until I took it on the highway. Now when I'm going 65+ the car jerks back and forth when I am applying very little gas. If I accelerate harder it stops, if I take my foot completely off the gas it stops and if I go into neutral it stops. It is more violent when I am going downhill but noticeable on flat ground. The only code I ever got from the car was about a year ago for an o2 sensor but that went away and never came back. It is ever so jerky at slower speeds enough that passengers wouldn't notice but you really notice it on the highway. Oh and when I mash the gas at higher rpm I feel a noticeable vibration in the gas pedal that was not there before either. She's got 182000 but has always been trusty. Thanks for reading ,any feedback helps.

[tamim13]

Did you notice your idle higher than before you did the timing belt? Like around 2K? Also, do you notice that your power in your car comes only after you've reached around 3K RPM, until then the power seems less? I had a similar issue when I got my timing belt replaced, there were so much vibration, I knew something was wrong. The balance shaft tensioner was not lined up, if I remember right. I'm trying to find the article where I read, that you have to use a screw driver to line it up and if it goes in only quarter of the way, it's not right, it had to go in at least half or something like that. If someone else remembers this or can post information on this, that'll be great.

[Shimmy]

Actually no. I still idle at about 500 rpm, but I do notice that the idle is shaky. I notice when I look under the hood that my battery and coolant overflow tank are shaking quite noticeably. The power is still there on acceleration but once I hit above 4k I feel the vibration in the pedal. It's possible that it could be the same problem with different symptoms. I should look into it. Thank you for your reply.

[tamim13]

I think this video has some information on what was wrong in mine.

https://www.youtube.com/watch?v=UtTcRru-C-U