Just curious if anyone else has had this problem. Please excuse my lack of car knowledge if I get any of this wrong..

I have an impala (2000).

Car is jerking/tugging intermittently at highway speeds, but sometimes at lower speeds (usually around 20-25mph and sometimes 40mph). When cruise control is set around 60-70 the car almost always shakes. For some reason, the shaking isn’t as bad at 75+ MPH.

Immediately after I let off on the accelerator (on the highway) the car shakes and hesitates a little. When EGR valve is unplugged almost all tugging and shaking goes away.

My car has been doing this for about a year now - on and off. I’ve left the EGR valve unplugged for months at a time. Had the spark plugs and coils (I think?) replaced in march of ’08.

 

if you've unplugged the egr valve and the shaking/tugging went away then i think you just answered your own question. replace the egr valve. either that or get your catalytic converter checked. the converters on the impalas have a tendency to go bad.

 

I've read similar symtoms related to the throttle position sensor. When it starts to go, it doesn't know what you are doing with the gas petal. You might consider that.

 

Clogged cat? I agree with milwaukee

 

is the check engine light on? if cat convertors are bad, check engine light will come on and throw code p0430.

 

A stopped up converter does not throw a code. However, you won't go very fast very far if it is stopped up so that doesn't sound like the problem.

 

Go to a salvage yard an buy a used EGR, clean it and try it. If that is it (which it probably is) either use the junk unit or go buy a new one. Sometimes ya just gotta use common sense and not depend strictly on computers to do your thinkin' for you. (LOL) Hell, mechanician can be fun!!