JMAX95

My dad's 98 SE seems to have developed low idle (500)when the car is warm. It's an auto and has around 50k miles.

My guess is maybe a dirty air filter. I wanted to get some other suggestions before I checked it.

Thanks for any help.

Daniel B. Martin

Here is some text copied from the factory service manual.

"Idle Air Control Valve (IACV) -- Auxiliary Air Control (AAC) Valve

This system automatically controls engine idle speed to a specified level.
Idle speed is controlled through fine adjustment of the amount of air which
bypasses the throttle valve via the IACV-AAC valve. The IACV-AAC valve
changes the opening of the air bypass passage to control the amount of
auxiliary air. ... "

The correct idle speed is...
- 700 +/- 50 (automatic transmission, in Neutral)
- 625 +/- 50 (5-speed)

Here's the factory service manual component inspection procedure for the IACV-AAC.

1) Make this test with the ignition key OFF. Disconnect the IACV-AAC valve harness connector.

2) Looking into the valve connector with the latch at the top, you will see two rows with three terminal positions in each. They are numbered 1-3 (top row, right to left) and 4-6 (bottom row, right to left). Check resistance between the following terminals.
2 and 1.
2 and 3.
5 and 4.
5 and 6.
At a temperature of 68 F, the reading for all measurements should be approximately 30 ohms.

3) Reconnect the IACV-AAC valve harness connector.

4) Remove the idle air adjusting unit assembly (IACV-AAC valve is built-in) from engine. The IACV-AAC valve harness connector should remain connected.

5) Turn ignition switch ON and OFF, and verify that the IACV-AAC valve shaft smoothly moves forward and backward. If NG, replace the IACV-AAC valve.


There are other engine parts which play a role in maintaining the right idle
speed, but the IACV-AAC is the first thing to look at. Good luck!

JMAX95

I read the thread regarding high idle problem. Could this adjusted by the idle screw? I originally though 4th gens don't have such a thing because it's computer controlled.

Daniel B. Martin

Perhaps, and you won't know until you try. However, the idle screw doesn't move on its own. If the idle speed is wrong, something is causing it to be wrong. Personal philosophy: I'd like to find and fix the problem rather than make an adjustment which merely masks the symptom.