I drive a honda accord '91 LX.... It's seems to rev up itself while idling and returns to 1000 rpm i.e 1 on the rpm gauge, if I give the gas pedal a quick tap or I put it in drive. Any ideas on this one?

 

High Idle speed and Fluctuation troubleshooting

Leaking EACV- Disconnect EACV connector. Idle speed should decrease. With the connector disconnected block the hole in the intake port or pinch the hose from the air cleaner to the EACV. If the idle speed decreases the valve is leaking. This condition will not set a code. The ECM can only detect an open or short circuit. It also may clog it’s screen if it has one.

Leaking IAC- (Idle air control valve) Disconnect IAC connector. Idle speed should decrease. With the connector disconnected, block the hole or pinch the hose to the IAC valve. If the idle speed decreases the valve is leaking. May not set a code and may not be a codeable circuit on all models.

TW or ECT sensor- (engine coolant temperature sensor) voltage should be about 3.0 volts @ 60 deg F and between .55 & .7 volts @ normal operating temp. If the voltage is above .8 volts at normal operating temp, will cause rich mixture and high idle speed. May not set a code because it is not far enough out of its operating parameters. **Also this sensor will not read temperature correctly if coolant is low. (beware)

Vacuum leaks- a loose vacuum hose or leaking intake manifold gasket can cause high idle speed and/or fluctuation. Also check for bad PCV valve.

Fast Idle Valve- (if equipped) a fast idle valve that is sticking can cause high idle speed and fluctuation. Check it by removing the steel cap on the top and putting your finger over the hole in the middle of the seat under the cap or block the port just inside of the throttle body opening, when the Idle is fluctuating or staying high. When the engine is warm this valve should be closed. You can tighten the seat but it will also change the idle speed warm up values (closing).

Throttle valve- throttle position sensor voltage should be .5 volts with the throttle closed. Make sure the throttle valve is fully closed and voltage is within spec.

ECU-If all else is good, if you reset the ECU and the problem goes away temporarily, the ECU may be defective.

Verify that the cooling system is full of coolant and
there is no air in it.

Remove the air boot from the throttle body and cover the
throttle body with something that will stop the airflow
(your hand, tape) with the engine running. With the
throttle body covered and no air going into the engine, the
engine should stall. If the engine does not stall, look for
a vacuum leak. With the engine running and the coolant
temperature above 90 degrees F, verify that there is no
vacuum on the lower port in the throttle body. If it does
not lose vacuum, look for a faulty fast idle valve on the
bottom of the throttle body, as long as the coolant hose is
good and hot.

Verify that the base idle screw was not turned way out on
the top of the throttle body. If it was, set the base idle
and see if the problem still occurs.

The upper port in front of the throttle plates feeds the
Idle Air Control (IAC) valve and the base idle screw. If
the IAC is unplugged and the base idle screw is turned all
the way in and there is still airflow through the upper
port, check for a stuck open IAC valve.

 

thanx alot, though explanation is overwhelming, it seemed to narrow down the problem greatly.