Hello,
I have a 5 speed '98 GXE. Sometimes (on average 20-30% of
the time) when I put it in neutral at a stop light or stop
sign, RPMs drop to around 400 before bouncing back withing a
second to 800-900 (AC is on). Normal behavior is it should
only drop to 900 when idling with a warmed up engine. Any
tips?
Thanks,
Sameer

 

if u look at some of the other posts on idling... u'll notice that the normal idling rev is about 650 +/- 50... if u turn on the ac it is bound to jump a little bit more. as long as ur car doesnt stall while idling i'd say u dont really have a problem.

 

The 400 dip isn't normal though, but I dn't remember what people have said was the culprit.

 

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. ... "

You may make a quick test of your IACV-AAC in the following way. With the
motor at normal operating temperature, and at idle, switch the A/C from
"off" to "maximum". Keep your eye on the tachometer as you do this. The
idle speed should dip momentarily and then recover. If it does this, the
IACV-AAC is working. If the idle drops and does not recover, the engine
may stumble, falter, and stall. The IACV-AAC may require cleaning,
adjustment, or replacement.

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!