1999 Honda accord at start up idles rough and low. (check engine light on)
After it warms up idles good just on start up.

. Check for codes.

. Clean Idle Air Control Valve:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-7.html#post1054149

. Clean throttle plate and throttle body. Afterwards, clean air box and replace air filter.

. Set idle to 700 rpm.