Maybe intermittent ignition. But more than likely it's a sensor. Possibly an o2 sensor. I've also heard of the EGR doing this too.
a longer cam shaft will make a car idle rough
bad battery
the timing,air hoses,relay switch maybe.
Check your map sensor
Make sure you have the right key because the door key will turn the ignition but won't start the car.
Depends on the car....what is it???
If you didn't put it back on right or maybe left something off like the rotor, sure.
does it happen a few seconds after you start the car? on my 1988 new yorker,it was the hydrolic pump that is on the right side of the trunk. i just unpluged it.
Make your car payments.
That is the air compressor for the ride leveling feature. It adjusts the rear air shocks when the back seat is occupied, or when passengers get out.
Could be a very plugged up fuel filter or catalytic converter.
A damaged fuel pressure regulator can cause a car not to start.