Need Advice 3.2 vibration
 

Background, '86 3.2 Carrera, 98K, well maintained.

Brought it in to my regular shop for a Valve adjustment,oil change and DE tech inspect. Mechanic called me after the his test drive and said there was a "miss" and asked if it was there before bringing it in. He noticed that it went away as the car got warmer and has theorized that the head studs are loosening with age and could break soon and that as they heat up they seal and the situation improves.

I noticed a vibration on the way back from the shop that seemed to go away as the car got warmer. Subsequent drives showed a significant vibration and "flat spot" form approx 3500-4200 rpm, that got better but did not go away when the car got warm.

Power seems good, even a little better than before the VA.

Has anybody heard of the loosening head studs in the 3.2? I thought they were either broken or good. I searched the site and can't find any mention of this. This theory comes from an experinced and well respected shop.

Is there anything they could have done during the VA to cause this?

I'm going to check out some other things one my own to try to solve this. Any ideas on twhere to start?

All inputs apprecaited.

My guess is they re-torqued the studs and pulled one loose. If so they should say so.
Mis & dead spot... something not right. Poor valve adj as well??
Just my $.02

As for the flat spot. Does it almost go away if you accelerate heavy through that range and become more pronounced if you're light on the gas? Mine did that exact same thing and it turned out that it was from an O2 sensor that needed to be replaced coupled with the AFM needing to be adjusted. I'd also throw in a bottle of Techron or BG44 to clean up the injectors.

My theory, your mechanic doesn't know squat about what head studs on a 911 do or don't do. I'm with Ken, I wonder if they screwed something up.

I think what you're saying is that the "stretched but not broken' theory doesn't ring true( doesn't sound right to me either).

Did they break one themselves and are trying to cover? ( I'll give them the benefit of the doubt at this point).

Could they have dinged something during the job? O2 sensor? Exhaust leak?

More inputs welcome.