Did you use good spark plugs? If the car calls for platinum, did you use platinum? Did you check the gap on each of the new plugs before installing? Did you torque them down properly? Did you reconnect all your plug wires in the right order?
I don't think there's any way that new spark plugs can affect timing, per se, but they can certainly affect combustion and engine performance. If your plugs are wrong, or are gapped incorrectly, the engine may run roughly.
But, what do I know, I prefer my spark-plug-less 240D. Only recently have I also owned a gasoline-powered automobile.
'83 240D, 250k miles