Rough idle My car idles rough after sitting and not running either over night or several hours. I must rev above 1500 to keep it running smooth. Once the engine reaches normal operating temperature, it idles fine.

Have you had the throttle valve cleaned?

Here is the most common cause of surges and stalls, it is the idle speed control air-bypass valve and throttle valve, they get full of gunk over the miles and cause idle issues (stalls) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

It sounds like you don't have the right fuel mixture and first thing you never told me the make of your car and the type of motor which is important but I'll give you a good long shot answer sounds like the fuel is not burning off I would get me a can of mass air flow sensor cleaner and follow the instructions the mass airflow sensor determines the amount of air and the computer raise the amount of gas to know how to regulate the mass airflow sensor and also clean the throttle body hope this trip works thanks