Quote Originally Posted by 89Vette View Post
Today, I noticed there's some vibration as it's revved in park -- especially when cold. Though it's possible a tune-up (or injector service) is necessary, it's not really a miss. I'm still thinking bearing(s). I confirmed this by kicking it out of gear on the hwy too. The effect directly corresponds to engine revs.

Because I'm also hearing a bit extra noise at startup, I'm leaning toward an engine accessory bearing issue. It's [somewhat] reduced after warm-up.
As I said, engine noise seems the primary cause. Remember my post asking about air pump noise? I took it by an Isuzu service facility today. Tech took a quick listen. Immediately, he said intake gasket(s) leak. I asked if that would account for roughness at 2500. He also said motor mounts could be part of the issue.

This could be a combo of all 3. A little gear noise, a little mount vibration, and an accentuation by the intake (to create an imbalance in cylinder power).

Are intake gaskets really a [common] problem on these? The tech said it was a problem in general with the 3.5L motor.