i got a 98 civic lx non vtec. bone stock. d16y7
5 speed

the idle bounces from 1000 to 2000 only during idle
it only does it when the car warms up. sometimes throws check engine code P0505.

when it throws the code the rpm bounces from 1300 to 1500 but a bit faster and the car jerks when giving it a bit of gas similar to if you let go of the clutch too fast.

once i clear the code the acceleration goes to normal but the rpm goes from 1000 to 2000 again.

I did the following:
the coolant bleeding procedure
changed MAP
changed IAC
changed ECU
changed fuel press. regulator
cleaned throttle body
changed thermostat
checked wiring for MAP. its good
changed intake manifold gasket
changed throttle body gasket.

if anyone can help id appreciate it. ive been working on this problem for months with no success. i need to pass emmisions test soon.
also if anyone could send me or post a vacuum diagram for my car that would be great.

 

I know you've already checked many parts but you should keep looking for a vacuum leak. Spraying some fluid onto a vacuum leak will usually affect the idle and that's how alot of people locate them. Some people use starting fluid, carb cleaner, wd-40, etc. A dab of grease can work similarly.

 

The idle changes when the CEL hits because the ECU switches to open-loop mode. It doesn't happen when the car is cold because of the extra air introduced for fast idle- the same reason the rpm doesn't bounce when you give it enough gas. The vacuum diagram is often on a sticker on the underside of the hood. If you don't have it you might be able to find it quickly in Google images.