I've noticed some interesting (at best) behavior on my 2002 Grand Am SE,
2.2L ECOTEC 4-cyl engine when coasting in neutral.
I recently moved into a house in a semi-ruralish, not-yet-developed (and
hope it stays that way) area with extremely little traffic, at the
bottom of a hill. Driving home, I get off the main highway, which runs
along the top of this hill. I discovered that if I put the car in
neutral, I can just coast this way with the momentum keeping me at about
35 MPH (which happens to be the speed limit), having only to apply the
brakes lightly at the end when it's time to pull in and park.
However, I noticed that frequently, but not all the time, the car will
slow down smoothly as I apply the brake, only to LURCH forward HARD
right at the moment the speed of the car drops below 10 MPH. It feels a
lot like a 100-pound weight or so has suddenly shifted forward in the
engine compartment and hit the front of the frame, stopping hard.
However the car will never do this if I leave the gear in Drive and
similarly coast (though I then find that I have to tap the brake on
occasion to keep me at or below 35 MPH).
I had thought it might be something peculiar with the car, perhaps
faulty engine mounts, but lo and behold, I discovered that my 2004 Chevy
Cavalier, with the same 2.2L Ecotec engine (but I don't think it's the
same transmission, not sure) exhibits the EXACT same behavior.
Also I recently had the opportunity to rent a 2005 Chevy Trailblazer,
and for grins, I tried the coast with it. It did NOT lurch when I
coasted in neutral. It has the Vortec 4200 Inline 6 engine, though, and
is signifcantly heavier.
Anyone know what's causing the lurch? The cars don't seem to be any
worse for wear, but I've stopped doing the Neutral coast, just in case.
E-mail fudged to thwart spammers.
Transpose the c's and a's in my e-mail address to reply.
Click to see the full signature.