Can we recycle?

(From New Straits Times (Malaysia))

Dear Paul, I own a 1.8 1996 Wira DOHC/4G93.

1. My car emits stinging exhaust while idling. What could be the cause? 2. Will leaning much cause the engine to save fuel? 3. How can I know air-fuel ratio is at optimum by looking at plugs? 4. Is it true that by increasing the stiffness of the suspension, it will cause the tyres to wear faster? 5. What is the function of TPS (throttle position sensor), and is it important for engine performance? My car's rear suspension is quite stiff, and obviously is much higher than standard setting. Should I replace the rear with softer springs and harder dampers, or harder springs and …