Inherited this Volvo from mother in law who passed while the car was in the shop having a valve job and timing belt, water pump done.
the car never felt 100% since we got it out of the shop.
replaced the radiator as somehow, the reservoir tube (plastic) had a hairline crack and I was replacing coolant every other day.
car has a misfire at idle runs okay from 10 -50mph. Above 50, the whole car shudders to the point of jarring my teeth out.
replaced the coils and plugs same symptoms.
Not sure where to go next.

 

did you check the valve timing? sounds like it could be one tooth off. What year? its not uncommon for people to mess up the VVT gear timing on the 2000+ models.

 

You've got a dead miss, and you need to treat it like a dead miss. You need to determine which cylinder is missing. That's easy.
There could be many causes, but for starters, you have 4 wires that need to work for one cylinder. Two to the coil and two to the fuel injector. These wires are tiny. verify.

 

1t's a 99. Car had a "complete valve job 50KM ago by a former Volvo Tech. I pulled the plugs for examination and out of curiosity. #4 was fouled beyond belief.
replaced the plugs which were Volvo plugs. Replaced the coils as all were original.
When removing the cover, the smell of fuel was noticeable. Wondering if I'm not heading for another valve job.

 

Well, now you know the problem was ignition, and you know which cylinder. That's good.

 

Replaced plugs and coils. Replaced injectors and torque mount. Misfire pretty much gone (GOING to clean plugs as injectors probably fouled new plugs). Replaced camshaft positioning solenoid.
car shakes violently between 53 and 60 mph. Shaking will decrease if I take either course of action: feather the accelerator (slowly exceeding the 60 mph zone or stomp on the gas to pass the 60 mph mark.
perplexed with this problem. Many of us are scratching our heads.

 

The shaking is perfectly normal for a car with a misfire. The symptoms are very much not confusing. However, if it was misfiring, the check engine light should flash. The car knows reasonably well when it misfires.