My 1991 Honda accord runs perfect but idles up and down all the time when is in the parked position.

Cleaning Idle Air Control Valve (IACV)

In order for Hondas, and many other modern-day cars, to idle properly, the IACV needs to be cleaned. Here's how to perform this simple task:

1. Remove IACV electrical connector.

2. Remove both bolts (12 mm) securing IACV to plenum.

3. Remove both IACV hoses.

4. Clean IACV and hoses with a spray can of brake cleaner--be sure to wear safety goggles.

5. Install new O-ring, if necessary.

6. Remove air intake from throttle body. Ensure upper and lower throttle body ports are clean. Dirt tends to build-up around top port.

While you are at it, clean the throttle plate, throttle body, and air box; afterwards, install a new air filter.