Put the car in the garage on Saturday and it was running fine. Went to go to work this morning and it was idling very rough with a nasty "clatter" noise while idling. The clatter sounds like a metallic bearing type sound... it only makes the noise at an idle though. When you accelerate and get up to cruising speed the engine sounds fine. I'm thinking a spark/ignition type issue. If it was a rod bearing or a lifter the sound would remain and increase with acceleration. The car is old, with @236k on it. Give me some ideas to check with simple work before I look at pulling the engine or major overhaul type things.

Clattering only at idle is typically a harmonic balancer. The outer rim of the pulley tears away from the rubber damping material. Think of it as the inner hub and outer ring of belt grooves with rubber poured between to dampen vibrations.

If you park in the garage, there should be evidence of rubber dust on the floor in that area.

Inspect the face of the pulley for tears and cracks around the outer edge of the face.

Thanks, I did not think of that, as I had one go bad like that several years ago. And it really messed up the timing. I do have another HB laying around the garage....I'll check it and switch it out if it'* a problem. Any other ideas to check in case this isn't it?

Sure.

Start checking around for a new motor if that isn't it.

Found the problem when I got home from work....AN easy solution. As I listened I detected a vacuum leak. I ran it down to the the vacuum lines attached to the top of the upper intake manifold where there is a bolt holding down plastic 3 way vacuum fitting. One line goes to the Brake Booster, the others go down to the Tranny vacuum connection. Anyway, the bolt in the fitting was GONE, leaving just a hole. I looked around and found the bolt laying down on the bell housing. The threads of the upper intake are stripped and it worked it'* way out. I'll tap the hole, and see if I can get a solid fit. If not, I have another upper intake in my junk in the garage. In 1991 the piece was still made of aluminum, and not the composite plastic they went to in '93! Amazing what a vacuum leak will cause an engine to do!!