Shakin' All Over

[monzacoupe]

I've been driving the 'coupe off and on for the past month or so and it's been going fine for the most part, tranny making lots of noise, but I will do the rebuild in the fall. My biggest concern is that at idle, the motor is shaking like a leaf in a stiff breeze. Is this because it needs a tune-up/timing check? What would cause this? It smooths out at revs above 1000-1200 or so.

Rick

[cammerjeff]

Is it a 2.5 Iron Duke, or a V-6? Either way I would check the condition of the Motor Mounts and trans mount 1st. A bad trans mound can cause a lot of shaking side to side at idle. If it is a Buick V-6 even the 77 and later even fires do not idle very smoothly, not like a modern V-6. But other than mounts, an ignition problem can cause it to shake, to low an idle speed can do the same thing. I have found the Buick 3.8 in my 78 Sunbird likes to idle at around 850 RPM a couple of hundred higher than the factory specs. at 600 it tends to shake a lot more.

What I found on my Sunbird causing it to shake very badly at idle, and have almost no acceleration was the Torque converter was actually bad, it was stuck and not doing any torque multiplication. But that is a very rare issue, usually found on a car that sat for many years. And that described my car before I bought it.

Give us alittle more info, besides engine type and size, Auto or manual? If an auto does putting it park or neutral affect the shaking? Compared to idling in gear. What is the Idle speed? More info never hurts.

[monzacoupe]

OK, I've got the 3.8l V-6 with a four speed. Idles around 800 I think. It sat around for a year or so while I was working on various things on it.

Rick

[cjbiagi]

I would suggest a general tuneup first if it hasn't been done in awhile. Plugs, wires, PCV valve, fuel filter, distributor cap and rotor are a good start. Check the condition of the weights and springs under the rotor to make sure they are not excessively worn or sticking. The weights should be lightly lubricated on the pivot pins as well as on the bottom of them. You may also want to replace all of your vacuum hoses as they can get hard and develop cracks that are difficult to detect. Also check the ignition timing and the condition of the vacuum advance module. If that is leaking and erratic it will run rough and shake. Obviously bad engine and trans mounts could cause a shake as noted. You may want to try swapping your vacuum advance hose from a ported source to a full time vacuum source or vice versa. Also check for any other possible vacuum leaks around the carb base and intake manifold. Also try adjusting the idle mixture screws at the base of the carb, adjust them for the highest vacuum level or rpm and then readjust your idle speed. These things should get you a reasonably smooth running engine assuming there are no internal issues.

[OldsStarfire]

Rck - this is just how the V6 manual tranny cars are. In my experience nothing will make it go away. It's just not a well balanced motor. I had my entore rotating assembly include clutch balanced and it's still there.

Many yrs ago a guy came up to me at a show and told me he worked at a dealer in the 70s and customers were contantly bringing their V6 manual tranny cars in for tune ups, but it was just that poorly balanced motor and there was no fixing it.