i have a 1990 honda accord. when you start it, typically after it sits for about 4 hours or more, the engine revs up and down. it will go between 2000 RPMS to about 0. and it will allmost die, then it revs back up. on a really cold morning it will actually die a couple times. and i have to restart it. but as soon as the engine is warmed up its fine.
I heard this could be Idle air controll valve
or another possibility is the return valve to the gas tank is broke, so the fuel is draininbg back to the tank, and it takes it a minute to get fuel lines pressurized, so it will run normal.
This is really frustrateing and i could use some help.
also while im posting this, sometimes during the summer, it will start up and immediatly die. it wont start back up, untill it sits for a while. if you let it sit for about 20 minuets it starts right up. it only does it rarely, and mostly on warmer days. any suggestions???

 

Check your PCV valve and vacuum lines also

 

Click on Accord FAQ at the top of the page, look for the write up on how to clean and adjust the IACV and FITV. IACV controls idle speed via the ECU, and the FITV is a thermal device, controlled by coolant temp to determine if the engine needs more or less air when cold.