Hi all,

I have a '76 Cutlass w/ original 350 - Seems to be 54k original miles. Timing gear had all its plastic teeth with no cracks and I just did a compression test and it had 150-151 psi on all cylinders. Seems good?

I have a little shake at idle when sitting at a light I'd like to get rid of. Any thoughts? I just replaced ignition (coil/cap/rotor/plugs). I know vacuum leaks can cause. I disconnected and plugged the power brake booster, no difference. I replaced intake manifold gasket about a year ago. I don't think I'm just idling it too low.

Where to start? Could it be idle mixture on the carb (Carb is an NOS one I got off ebay. Its been on the car about a year - seems to work great but I never tried to dial in the idle mixture).

Do old motor mounts dry out/ get hard and stop absorbing vibration? (Seems like a long shot). Egr? (Mine is original).

Thanks for any insights!

 

How about wires ?

 

Hook up a vacuum gauge and look for a bouncy needle.

 

Those are good compression numbers. As said, adjust the mixture screws for the smoothest possible idle and at least inspect and ohm test the plug wires. Put a tach on it, it may be idling lower than you think. If that does nothing and no vacuum leak is detected, try switching from ported to manifold vacuum for the vacuum advance. It adds more timing, which these high 7 to 1 Olds V8's like.

 

Bad vacuum advance diaphragm can cause a lean mixture on one cylinder. I was all set to do a valve job once on a '78 Olds 350 fount the bad diaphragm- replaced it and all smoothed out, easy to check ...

 

Superb !

I would definitely confirm drive idle rpm as olds 307 and 403 suggested, first.

Factory setting generally kept climbing on 4bbl 350s 1968-1973 at a minimum.

Automatic drive idle.
1968 = 550 rpm
1969 = 575 rpm
1970 = 575 rpm
1971 = 600 rpm
1972 = 600 rpm
1973 = 650 rpm
https://www.teufert.net/olds/olds.pdf

My 69 starts stumbling and bumbling from 550-500 rpm. Let it drive idle a bit too long at 500 rpm and it's going to turn off ...

 

I personally like 750 rpm in drive, 1000 rpm in park, way more stable. A bad vacuum advance can cause cold stalling, seen it before on a sbc. Actually the vacuum advance worked but the lever arm was seized. A leaky choke pull off also can a shaky idle. Saw it on a 307 Vin Y, somehow still worked to open the choke but enough of a vacuum leak to cause a shaky idle, it was weird.