I have a 98 Civic DX D16Y7.
The engine is surging when it is cold. Engine code P1509.

Once the engine is warm, you can shut it off and then turn it back on again and its fine. You can then let it sit for a couple hours and it is still fine.
It has been getting progressively worse. When it first started doing it, just restarting it usually worked. Now you have to let it warm up.

I have taken off the IAC and cleaned it well.
I have done my best to make sure the air is out of the coolant.
I have replaced the Coolant Temperature Sensor.

I figure if it was an electrical or vacuum issue, that it would be more consistent.

Thanks for any help.

 

I replaced the IAC valve and it resolved the issue.