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.