1997 Honda Civic Idle problem

CHLAROCK

MEMBER
1997 HONDA CIVIC
4 CYL
FWD
AUTOMATIC
150,000 MILES

My 1997 civic lx starts fine but after about 2 or 3 minutes the idle reves to about 1000 rpm then drops back to normal then reves again then back to normal. This continues on a very rythimc basis. Is this the idle air control valve or could it be something else?

5 Replies

SERVICE WRITER

MECHANIC
9,123 POSTS

Coolant is full?

1.5 motor?

IF so,

This car has an aux. Cold start air bypass valve in addition to the idle speed motor. The bypass valve gives it a high idle when cold. It may stuck in the open position. It is near the bottom of the throttle body. A quick check is after the car is warmed up remove the intake hose to the throttle body. There is a hole about 1/2 dia. In front of the butterfly. It should not have any suction! If it does the bypass valve is bad. When car is cold it will have suction, but after it is warmed up there should be none.

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Thursday, June 4th, 2009 AT 6:52 PM

CHLAROCK

MEMBER
3 POSTS

Coolant is good
1.5 motor
I don't see a hose on the throttle body as you decribed. The only hoses I see are going to the IAC valve. I started the car, ran for a couple of minutes till it started to rev funny, which now that I did it again notice the idle DROPS not REVS higher (like I previously described) rythmically. I had the air filter off and if I put my finger over the AIC valve opening to block it about 2/3, the problem stopped. The idle leveled out to normal and stayed there. Would that indicate a bad IAC valve?

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Friday, June 5th, 2009 AT 12:55 PM

SERVICE WRITER

MECHANIC
9,123 POSTS

Must have been a change in years.

Since you are controlling the valve, I would think the valve is bad.

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Friday, June 5th, 2009 AT 8:32 PM

CHLAROCK

MEMBER
3 POSTS

Should there be any anti freeze in the hose that connects to the IAC valve? I had a small amount run out of the hose when I pulled it out. What could that be from?

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Tuesday, June 9th, 2009 AT 7:42 PM

GWL

MEMBER
1 POST

Yes, coolant does run to the IACV. You can try to clean the screen with carb or brake cleaner. Let it dry out before you put her back altogether, be sure to bleed out all the air. Just run the motor without the rad cap, run the heater at high temp, and let rad fan cycle a couple times.