Weird Bucking issue

[monkeyodeath]

Noticing an odd phenomenon with my 325i.

When i'm in a low gear, moving slowly, and let off the gas entirely, the car starts bucking back and forth pretty hard.

When I hit the brakes, the clutch, or give it some gas, the bucking stops.

Also seems to buck backwards pretty noticeably when shifting gears. Push the clutch in, and it lurches forward. Let it out, and it lurches backward.

RPM doesn't seem to rise or fall appreciably when it's doing this - i.e. the needle doesn't bounce with the car, stays steady. So I can't tell if it's the engine or something else.

Is this a suspension issue? Something with the transmission? You can definitely hear a whirring sound when you're in neutral with the clutch out that disappears when you push the clutch in. Diff issue maybe? I know my diff is a bit noisy.

[discopete]

i have a similar lurching motion with my 325i...any insight would be appreciated!

[bmwguy325is]

Well if its noisy in neutral its input sahft or lay shaft. You may have a bad tranny. Dose it leak at all? Or maybe you have bad u joints and they are binding.

[discopete]

Mine is not noisy in neutral and doesnt leak. Tranny feels pretty good so i would be more inclined to move towards u joint problems. These hard to fix/expensive?

[monkeyodeath]

The tranny doesn't leak. It's pretty whiney in 1-3 gears - sounds like you're in reverse, the way it whines. And I know that the diff bearings are on their way out, slowly.

Still, the clunk comes from below the car, either in the driveshaft or diff area.

I'm thinking either driveshaft issues or that the tranny/diff has a ton of lash in it.

[gtdragon980]

If the rpm's drop too low while in gear, the car will buck. It's because the rpm's may be going below the idle rpm's so the computers natural counteract is to send more fuel and keep the engine moving. I'm not sure if this is exactly what you mean, but it sounds like you are just going tooo slow for the gear and the car is doing exactly what it would do. my car does the same..

[b*saint]

ROFL its normal people. Youre in FIRST GEAR. I'd like to see you try and go 30 mph in first gear on an RC51. It bucks so hard, you practically get thrown off.

[Mr. Tasty]

Such a worthless thread
Lol

[bastianshaw]

No. Hella good thread my car does it too, in first it's a real mechanical issue that ONE OF my cars has and the other doesn't.

[b*saint]

No. Hella good thread my car does it too, in first it's a real mechanical issue that ONE OF my cars has and the other doesn't.

All the same cars?

[Bimmerista]

Throttle position sensor

[monkeyodeath]

I'll have to check out the TPS.

I think some people are misunderstanding what I'm talking about - I know all cars buck a lot with throttle in first gear, I'm not stupid and I've driven plenty of manual transmission cars before.

The thing that mine is doing is bucking in first gear at low speeds, when I'm completely off the gas.

For example, say I'm in traffic and I'm creeping forward. My car will start bucking unless I add some gas. Driving through parking lots slowly - same thing.

I've never had a car that does that - and I've owned some pretty torqueless vehicles. It seems odd to me, especially considering that first gear on this car is pretty low and the engine is pretty torquey.

[b*saint]

Ive had cars that do this, so I guess my cars were broken and I figured it was normal. :?

[walktheboard]

what is your car idling at?
sounds pretty normal...

[cabriodster87]

My car will do it, i can even make it happen in second gear. I think it has to do with how much play you have in your drive-train. Seems like a Doppler effect on the components as it loads and unloads torque at a certain frequency.