I have a 1996 Honda Accord. I recently had a problem with an extreme erratic idle. It seems to only do this when the engine is cold. Once the vehicle warms up, It returns to a normal idle. I recently replaced the spark plugs, oil, anti-freeze, and air filter, which had no effect on the problem. Any suggestions would greatly be appreciated. Thanks

Thoughts:

. Vacuum leak--check hoses and PCV valve.
. Fast Idle Thermo Valve.
. Check/replace igniter.
. Check Idle Air Control Valve.

Same thing happened on my car. Great answer !

Fast idle control valve on the rear of the intake manifold (has two small coolant hoses connected to it)

Did you ever figure this out? I'm pretty sure I have the same issue with my 96 accord. When it's cold, and I'm in neutral or have the clutch engaged, the rpm jump from 1000 to1800. After it warms up, it idles normally. I'd appreciate the help. THANKS!

Guns10685, try purging all air from the cooling system, by filling the radiator with coolant until it comes out the bleeder bolt. There are other ideas offered in the link below:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-7.html#post842969

Item 1 in the link is a must read.