It happens mainly in the morning, for a few seconds only.

The engine starts with vibration, like there's not enough gas to start, for less than 5 seconds. After this it runs normally.

And it would not do it again during the day if I am doing my normal routine, stop in a place for one or two hours, then go somewhere else.

I am trying to understand the problem. I picture a small deposit for gas that's supposed to be available for the next start. But if the engine has not started for a good number of hours, like overnight because it will happen every morning, the gas evaporated or leaked. OK, this sounds like from a carburetor perspective, I'm just trying to describe the issue. Maybe there is an electronic device dedicated to support the start only and is broken, but the rest of the start system and fuel supply works and I will have this shaky starts until I fix this problem.

Thank you in advance for your help.

Regards,

Sam

 

You didn't say what year your S60 is but there is a SW upgrade for the 2002 that adresses this problem

https://volvoforums.com/recalls-and-...d_2839/TSB.htm


There is always supposed to be some fuel pressure retained in the fuel supply system when the engine is turned off. On this car there is a check valve in the pump assembly. This prevents vapor lock, and hard starting. This problem normally shows up as rough running or no start when the engine is warm, which you don't seem to have. When the engine is cold, I think it results in a long cranking before it starts .

As always, first you should check for trouble codes when you start trying to diagnose a problem.