"Chugging" in 1st and 2nd gears

[mgwatson48]

Hey guys,

I recently BADLY grinded a 1 -> 2 shift (ordered RE mounts that night..). It might just be in my head, but I'm now noticing that at low speeds in 1st and 2nd gear, the car seems to be "chugging" when I apply the throttle slightly.

Anyone experience this?

Thanks!

[Walkurie]

It should be like a fine watch in 1st or 2nd. Mine will go below 5 mph, say 800-900 rpm, and not buck. Stock gears.

[mgwatson48]

Interesting. Good to know. Thanks.

[mgwatson48]

Bump. Car is still doing this. I notice that it's more pronounced when the car is cold and I'm in second gear holding steadying around 3000-4000rpms. Any ideas.

[StickMon]

There are a couple of speed/gear combinations where my car will go into oscillation.
2nd gear just under 4000 is one of them. Reminds me of a headstrong horse I once owned.
Have to either give it some gas or lift. Not sure if that's what you have.

[beta]

Read codes on your car, even if you don't get a CEL you might have stored codes that can point you in the right direction.

[mgwatson48]

Interesting stickmon, that does sound like what's happening with my car. I wonder why it does it?

Beta, good idea, I'll see if I can get a reader on it this weekend.

Cheers

[StickMon]

I've scanned it with DIS a few times and, while I found some wacky things, nothing in the engine management. Car stores lots of codes on the ABS, DSC, wheel speed sensors after being smogged.

I just figured it's an artifact of the fly-by-wire throttle control system. At certain combinations it has, as we say in the Engineering biz, insufficient phase-gain margin. Loop has too much gain and too much lag, so it keeps over correcting and goes into oscillation. Kinda like when you over correct the steering input in a slide, and have a "tank slapper".

[beta]

The reason I suggested codes is that a few people have had throttle position sensors go bad; there's 3 parts to it: the pedal itself, a relay at the front of the engine (you can see it without removing anything) and another switch that goes inside the manifold.

If you did have a throttle position code, you could take out the throttle pedal and test it with a multimeter. There's a similar thread here.

[mgwatson48]

Thanks for the input guys. The car is at the dealership for warranty work right now (glovebox). So when I go to pick it up I am going to take the foreman for a test drive so he can first-hand see what I'm talking about. Ill keep you guys posted!

[Westersund]

I get this on my M to, but only when cold. And only if I accelerate slowly.