Bad balancer? Torque convertor?

[Irish1941]

Maybe you guys had this.
I get this weird vibration/resonating on start up. Around 1700 I'd say (no tach on the '89). The vibration comes in for 1-3 seconds and goes away then comes back 3-5 seconds later. Revs don't increase.
Doesn't seem to be there under throttle when stationary or moving down the road. And when it's warm & idling, no vibration.
Didn't see any signs of balancer movement and it seemed tight.
Trans fluid is up.
Check motor/trans mounts. All good.
It's an '89 350TBI/700R4/241 with 138K on the clock.
Any ideas?

 

[cuervo]

When you say vibration are you talking about the engine shaking or there is a noise you hear?

 

[Irish1941]

Got it!

I didn't think it was visible until looked this morning. Engine did have a slight shake. Checked all the vac lines and all was good. Injectors looked good.
Pulled the IAC and cleaned it up, stuck it back and shake was gone.
Had a pile of crud on the plunger and it wasn't letting the needle seat all the way. Glad it was a simple fix this time.
Thanks the reply.