What type of vehicle is it? usually an irregular idle is caused by a vacuum leak (high idle for the most part) now a surge could be a problem in your coolant sytem it will need to be bled to stop the surgeing and this is usually a long and slow surge but if your surge is quick or rapid this would most likely be your iac (idle air control) valve typically located on the throttle body. a quick way to check if its working is to take the tubing off and put your finger over the first hole in the body see if its sucking (should be very strong vacuum pressure) reply with more details on the vehicle and whats going with it.
Here are the common cause of idle surge, cold stalls, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours.
To correct this problem I want you to get a can of intake cleaner (ABOUT $5.00) from any local auto parts store like NAPA or Carquest, do not use carburetor spray, intake cleaner only or u will damage the Teflon coating inside the throttle valve and air bypass valve, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won
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