Engine Vibration (ARGH!)

[TachyonS14]

Alright, heres the deal... I have a 97' 240 and I am getting an engine vibration. When I first start up the car, you can't feel the vibration because the idle is kicked up because it's cold, but once the engine gets warm the vibration becomes very noticeable and the steering wheel shakes violently. But, if I turn the a/c on, the vibration is slightly there, but very hard to tell. Same goes for driving with the a/c off, It's really only noticeable when sitting at a stop light. Once I get off the line it's hard to notice the vibration.

So, I've taken measures to get rid of this problem. I've changed my spark plugs, and plug wires (factory ones), left, and right motor mounts (factory), PCV valve, and cap and rotar. Whatever I do, I just can't seem to get rid of this problem. I've been told to clean my throttle body, haven't done that yet. Maybe a butterfly valve isnt opening? Also, this may give some insight to the problem... When the car is warmed up and I have the a/c on, if i turn it off while at idle my rpms with drop to around 300-400 almost stalling the car then it will jump back up to where it's supposed to be. Maybe have a valve job done? I've checked my timming and it's set at 20 degree's... Also I've been told to un-plug my TPS sensor and then adjust my timming accordingly... Can someone show me where the sensor is? My chiltons sucks.. Thanks for reading, any and all suggestions are welcomed.

[NISTECH]

the tps is mounted to the side of the throttle body has 2 connectors hooked to it one brown and one gray. When your car is idleing to the point you have the vibration does the engine visually appear to shaking or does it look smooth?(minimal shake is acceptable)

[TachyonS14]

It has minimal shake, but the vibration is 100% engine related.

[NISTECH]

then you got something hitting the body of the car from the power train. check exhaust, anything along the firewall and over the trans in the tunnel. I suspect your gonna find something hitting. check all your a/c and brake vaccum piping as well.

[TachyonS14]

I've had all 3 mounts replaced recently (left, right, transmission). I've looked under my car, nothing seems to be hitting. I will check for leaks though.

[TachyonS14]

Anyone else have any thoughs? PLEASE!

[Supafly]

i'm a little unclear on your description. do you mean the engine is just shaking as in your idle is so low it's chugging really bad or that you're hearing a buzzing coming from somewhere?

[TachyonS14]

My engine is shaking and causing a vibration in the cabin (IE dash, steering wheel). The chuggin only takes affect when the car is warm and i have the a/c on, and i turn the a/c off and the chuggin/choking goes on for like 2 seconds then it gets back to regular idle speed but the vibration still persists.

[NISTECH]

I really think a steel pipe to your a/c lines, your exhuast system somewhere along it or something above the trans in the tunnel is hiting the body of the car causeing the vibration you feel at a low idle. have someone sit in the car with the car idleing at the point you hear the noise. while they sit there and listen you go under the hood and start placing your hand on all the items that run from the engine to the fire wall and have them signal you when the noise goes away. when that happens your hand is on the part causing your problem. if that doesent work grap a pry bar or some other long metal bar and pry your exhaust down from underneath the car have them honk when you hit it. check behind your intake manifold between it and the fire wall when it happens see if something back there is hitting too.

[GroundZero]

or on the more gloomy side, the rotating mass of your engine might be unbalanced.

[TachyonS14]

You mean my harmonic balancer? I've thought about that, but I'd rather go through the easier paths before I start that project. Btw, NISTECH, thanks man, I'll give that a try.

[GroundZero]

no i was thinking more along the lines of the flywheel

[TachyonS14]

I just had the flywheel resurfaced, along with a new clutch kit... I'll see if I can narrow the problem down today.

[GroundZero]

did the vibration start soon after the clutch job?

[TachyonS14]

Way before the clutch job.