When I start my car (1991 Accord, automatic) the rpm jumps up to about 2000 but as soon as it's started (within a couple seconds) it jumps down to about 1000 (warm weather).

I've never seen that in a car; any other car I've driven the rpm goes up and just stays there without coming down extremely quickly like that.

Does anyone know why this would be happening?

Thanks in advance!

 

Too much air... Check for vacum leaks...should be some slack in throttle cable..Fast idle valve may need screwed in a couple turns. The base idle should really be lower than 1000??

 

vaccum leaks would be consistent.

i think its just your car is cold, even tho its warm weather, which is why it does it for a very short amount of time.

are you getting any cel ?
any other symptoms ?

 

from what ive read, most 4th gens are steady at 1k-1.5k usually, my 5th gen use to idle up to 2500 every cold startup, but after 2 cans of tb cleaner, its been idling at 2000-1800k area, pretty normal for a 130-140k car i would say...