When starting the rpm’s go to about two thousand and holds for a few moments, then it will drop to seven fifty to one thousand and back up to two thousand. It will continue untill the engine warms up. After warm up it will idle fine. I have replaced the Idle solenoid. The other problem is it does not set an engine code. I have gone through the Honda repair manual, and have tested the coolant temp sensor, the air temp thermistor sensor, checked the High idle control,the continuity from the Idle speed solenoid harness to the engine controller, and everything checks out. In the manuel after all checks, check out it says to replace with know good part and see if it fixes it. That is expensive, that is why I put the Idle speed solenoid on. I also purchased a new computer, and it did not change the problem. If you could give any direction or other things I could check out,Thanks. Steveshs
This problem will likely outstrip my ability to help, but I can at least bring up a simple thing and bump it.
When you say you replaced the idle solenoid I assume you mean the idle air control valve (synonymous?). I believe that the ports on that are sealed to the manifold by o-rings. were those carefully replaced? And did you run new vacuum lines for it or just use the old ones? Were the vacuum lines crossed when you hooked them back up? In other words, make sure that everything re: the idle control valve is sealed up and not leaking any air (or backwards).
While you’re checking that, check the port openings to the intake & make sure they aren’t clogged/restricted.
I have cleaned every vaccum port on the intake, and have taken vaccum gage readings, all are clear, I have also checked all the vaccum hoses to make sure there are no restrictions. I did find if I disconected vaccum line #21 to the Map sensor it will quit pulsating and if I apply 10 inches of vaccum to the map sensor it smooths out. So I installed a new map sensor, no change. As for vaccum leaks I have sprayed carb cleaner over every inch to check for vaccum leaks. Confounded.
Hi Steve,
I had a situation which is somewhat similar, but also confounded me. I have an '88 Honda Civic WGN 1.6L 5 spd. Starting cold at 1600 RPM as the engine warmed it would oscillate between 800 RPM and 3000 RPM. I did lots of trouble shooting, checking vacuum leaks, etc., not as extensive as you have done. My local Honda parts people suggested that I replace a temperature sensor on the driver’s side of the engine block that sends engine temp to the computer. That solved my problem.
Good luck! 
Captain Jack
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