Spark Plugs - signs they need changing
 

My 92 200TE idles a bit low and rough and gives intermittent throttle delay, possibly misfiring. I just bought it recently and it is due a service based on mileage around now but the last service was recorded 2 years ago. Suprisingly my mechanic set me off on a series of time consuming and costly investigations on the engine, auto gearbox, exhaust etc to solve the acceleration problem. I have come up with nothing and only now seem to be looking at the more obvious things. What are the typical tell tale signs that your car may need new plugs or a new oil filter etc. Could this be my problem?