My 1994 850 Turbo wagon was just diagnosed by Volvo with a bad intake valve on cyl.5. They said that the valve could be bent. When they took off the timing belt cover they noticed that the intake gear (top right one)was out (ahead) by 5 teeth. They had no explanation for this, none. That really bothered me. Well the car does start and can be driven, it just feels and runs very rough, especially at idle. Imagine running only 4 of the cylinders rather than all five. I have a friend working on it now, we took off the intake manifold so far and the right intake valve in cyl.5 was all black. The rest, including the left IV in cyl.5 all looked the same, pretty clean and normal.

But what I need to know is:

1.- what caused this to happen?

2.- what should I look at doing to prevent this from happening again? (one friend suggested the timing tensioner)

I should also add that there were no warnings. No funny engine noises or error codes. The car did smeel a little rich though and maybe lacked a little power. I was driving home from work on the highway and noticed the engine shaking at a 100km/hr. When I came to a stop at the end of the offramp the car was displaying the symptoms as mentioned above. The car also had new plugs, wires, cap and rotor as well as a relatively recent oil change.