Toyota Repair: 90 Corolla High Idle, intake hose, cold start

Question
I have a 90 Corolla 4A-FE 5 spd. with 335,000 miles. Its been it the family since new. No major problems.  The idle at cold start is 2500 rpm. After driving for 25 miles (to work) it will idle at 3500 rpm.  The warmer the engine gets the higher it idles.  It started doing this last summer.  In the warmer weather the cold start rpm was around 1500, going up to 2500 once the engine warmed up.  Thanks for any help you can give me. Also, the only code I've been able to retreive is code 51.

Answer
the code 51 is irrelevant, it just means that the a/c switch was on. The idle problem may be due to excessive carbon in the throttle body, removing the intake hose and cleaning the inside of the throttle body and checking the therottle plate to make sure it's not hanging up may help.