My gas pedal shakes on my C280
 

I've been trying to figure out why my gas pedal shakes on my C280. I've gone through 2 sets of motor mounts in 9 months, as that was thought to be the culprit. Also my steering wheel shakes along with the gas pedal. I've been through hi speed alignments at the dealership, front suspension basically rebuilt, but got this shaking problem. It's intermitent and isn't associated with a particular speed. Control arm bushings, the whole shabang is new underneath. Any thoughts gents? Also I have a new set of Michelins - no change.

Geoff

It is important that you tell us the year and mileage of your car. There are two very different C280 automobiles. There is the M104 engined 1994-1996 cars with inline six and four speed automatic. There is the 1997 models with M104 engine (inline engine) and five speed transmission. There are the 1998-2000 cars with M112 V-6 engine and five speed tranny.

Some of the cars are OBD-I and others OBD-II. I think some have conventional throttle actuation, and others have drive-by-wire.

Some thoughts include a possible misfire or fuel problem. Does the car suffer any other kind of symptom other than a shake through the pedal?

Sorry - I have a '98 C280 with about 55k on it. Like I said, 2 sets of motor mounts and also I forgot to mention that I've bee through 2 sets of control arm bushings on the front end. Thanks for your help everybody!

Geoff

Does the vibration appear related to road speed or engine speed? If road speed, the intermittant nature speaks of something related to wheels/tires/brakes. As you turn, go over bumps, etc, the dynamic relationship between the front wheels changes. If the imbalance phase angle between the wheels is low, you will get little oscillation in the wheel. As one wheel travels further than the other, the phase angle will increase, allowing oscillation to occur.

This could happen with very little imbalance though, if the root of the instability is elsewhere, e.g. improper wheel/tire combos, looseness in steering components, etc.

Steve

I think it's steering related - my steering wheel goes "sloppy" a lot if that makes sense. And it feels like I wander all over the road at highway speeds (accompanied by the shaking gas pedal, steering wheel, etc.) It usually starts around 60mph and continues through about 90mph. But as I decelerate, it continues through about 45-50mph. My mechanic is baffled.

Thanks for your responses

Geoff

I'd go through the steering components pretty carefully, starting with the inexpensive steering damper. Doesn't sound like the culprit, but since it's well under a hundred bucks, it's a good place to start. Tie rod ends, etc. Sounds like something is seriously amiss.

Two sets of engine mounts? Why? There is a way of measuring the clearance, and worn mounts are pretty easy to diagnose. Sounds like you might have a "parts tosser" working on your car. You'll need proper diangnostic work, ASAP.

Actually, i did have the steering damper replaced about 3000k ago - no help. I've taken the car to 2 dealerships and an independent shop, and they keep telling me I need I high speed balancing, which I've had at least 3 of. New tires already, no bent rims, etc.

Geoff

Wait a minute. Maybe the sloppy stering and pedal shake aren't related. Your car has drive by wire. I don't know much about the drive by wire, but I wonder if it's acting up somehow...

hhhhmmm

Sorry to hear about all this trouble. Most w202 owners I know have found their cars reliable. Me included...

Another note - going up slight hills and stuff the vibration seems to subside, then coasting down the other side it gets a lot worse. Does this help at all?

Thanks

Geoff Martin