Belt is probably not timed correctly.
timing off
Hopefully you got the timing marks lined up? What else did you add? Plugs? Were they gapped properly? Wires? Are they on tight? What exactly is "other things"?
You dont you replace the timing control module
Poor performance on takeoff ... rotten gas mileage ... rough idling ... hard starting.
Motor mounts are bad
Engine bounce is a phenomenon where the engine speed rises rapidly and then drops back down while the vehicle is idling. This can be caused by issues with the fuel system, ignition system, or engine timing. It can lead to rough idling and poor engine performance.
Rough idling is whenever the vehicle's motor "misses" or does not fire causing an imbalance and a loss of rotation reducing the motor's power and causing excessive shaking.
dirty injectors,water in fuel,exhaust leak, timing belt,universal joint.Check them all.
I experienced this problem after my car was leaking motor oil due to old faulty gaskets that needed to be replaced. Apparently because of the oil spreading everywhere it reached the engine mount. The oil combined with the heat from usage caused to wear down the rubber portion of the engine mount. I noticed the rough idling was gone once that piece was changed. Side note: It also helps to make sure your timing belt is well calibrated to determine proper idling. ANSWER: Another posibility is a vacuum leak or an air leak between the MAF meter and the intake plenum.
Timing Belts need to be changed around 100k miles or every 6 years. These are safe averages. Timing Belts like tires breakdown with age so it is not just a mileage issue.Other indicatons are an engine that runs rough when coming to a stop or idling. Worn timing belt result in trouble codes from the camshaft or crankshaft sensors, causing a dashboard warning light.
I believe the timing has to be off just a little! Or the ignition box is going bad. the module on the fender.
my 1990 300zx is idling rough what could cause this?