960 having some trouble starting

We have a 1993 960, it's been having some trouble starting up in the morning. It's just had its last major service maybe a month and a half ago, where they changed plugs, wires, serpentine belt, oil etc... Pretty big service, but everything is basically new, and in good shape, engine wise.

It is having trouble catching spark after a period of a good 5-8 seconds cranking, the car will then shake back and forth, like the engine is badly out of balance, or it won't catch... On the second attempt the engine is fine, and after its been warmed up, also fine.

I'm thinking weak battery, but my father things the timing is off - I then reminded him that the engine would run poorly at all times if the timing was off. No check engine light yet, we've seen these symptoms before tho, years ago.... Can't remember is the battery went tho.

I have a similar problem. I have a 1996 850 wagon. In the last week the car does not want to start when I first turn the ignition, but starts fine the second time, and runs very well. At this time of the year we have lots of tree sap, and I wash the car every day, purring lots of water from the hose. I thought that maybe the moisture is causing this. But lately few times I also let the fuel tank needle go down all the way to reserve. Maybe the fuel filter got clogged and it takes two bursts of fuel to start the engine. This second theory may be true. Yesterday I filled the tank to full, and I put some injector cleaner. I also tapped gently once on gas pedal before every start and the car started first time with no problems all day. I will change the fuel filter in the next few days, and wash the car again to see if the problem continues.