1991 Honda Accord engine idles erratically

NDREW2505

MEMBER
1991 HONDA ACCORD
4 CYL
FWD
MANUAL
250,000 MILES

The car idles up and down after running for a few minutes and continues to do so for anywhere from 10-30 min. Once the car gets good and warm(engine temp) it will stop by itself or if I cut the car off it stops until the motor completely cools and I start it again.

cars
a 91 accord ex 5spd. List of things ive tried so far for idling problem.

replaced air filter
replaced egr valve
cleaned iac valve
cleaned iac motor

the haynes manual lists a few things that could still be wrong but I wanted to hear from someone with a little experience b/c haynes doesnt go into depth on a lot of issues. Any help would be appreciated!

1 Reply

IMPALASS

MECHANIC
3,112 POSTS

Hello

Base off of what you say, I would say it is your fast idle valve. I have provided what the valve does and a check you can do.

The Fast Idle Valve, mounted on the throttle body next to the throttle angle (TPS) sensor, raises the idle speed when the engine is cold. The Fast Idle Valve is controlled by a thermowax plunger type valve. When the engine coolant is cold, the thermowax contracts the plunger which opens the valve allowing air to bypass the throttle plate and idle adjusting screw into the intake manifold. When the engine coolant warms up, the valve closes and the bypass air flow is blocked.

Test

NOTE: Do not attempt to disassemble the Fast Idle Valve, it is factory adjusted.

Start the engine.
Remove the cover of the fast idle valve.

Put your finger on the valve seat area and make sure that there is air flow with the engine cold (coolant temperature below 86 °F, 30 °C) and idling.
If there is no air flow, replace the Fast Idle Valve and retest.
Warm up the engine to normal operating temperature (the cooling fan comes on).
Check that the valve is completely closed (no air suction can be felt in the valve seat area).
If any suction is felt, the valve is leaking. Replace the Fast Idle Valve and recheck.