emax02

iTrader: (1)

My 95 Maxima{5spd} with 98K miles has been acting a little strange for the last 10-15K miles. When I start my car up it idles fine and then once it heats up and I hit the gas and put it in Nuetral the Rpms occasionly drop down to 0.3K and then sit there for about 1/10 of a second and then the idle goes back to normal. Usually the Rpm's don't drop below 0.4K though. Once the car has been running for about 10 minutes the problem seems to completly go away. I should note that after about 5-6 minutes of driving the idle still acts weird even though the car is at full operating temp{VIA on board gauge}. I thought maybe it's a bad o2 sensor? I just replaced all three of them and the car is not any better. Next I replaced the spark plugs{today} and the problem still persists? I also swapped my MAF sensor out of my 98 I30 and the car is still acts the same. I have also done the AC test and the car behaves fine. Any light on this situation whould be greatly appreciated.

BTW I changed the fuel filter about 10K miles ago. Could a dirty throttle body cause this or a old PCV valve?

ericdwong

I had the same problem during the colder months, the engine would bog down after a cold start. Wierd. Never figured it out either... no problems lately though..

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. ... "

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!

emax02

iTrader: (1)

Thanks a lot Dan but as I mentioned in my post I allready did the AC test. I whould have said the name of the test but I forgot it, sorry. Any other possible ideas that may be causing this? I really want to fix it my self. Thanks again!

Daniel B. Martin

You may want to test your Engine Coolant Temperature Sensor. This is easy enough, requiring only an ohmmeter.

On the 4th Generation Maxima engine the Engine Coolant Temperature Sensor is located in the water outlet tube close to the engine end of the upper radiator hose. There are two sensors in that area. The one nearest the hose is for the dashboard temperature gauge. The ECTS, the one you're interested in, is right next to the the gauge sending unit. There is a good picture of these sensors in the Haynes repair manual on page 3-7.

With the engine cold, disconnect the ECTS and measure its resistance. Reconnect the ECTS, start the engine, run it until fully warmed up. Stop the engine, and repeat the resistance measurement. The "warm" reading should be a much lower value than the "cold" reading.

The manual gives these specs:
Engine coolant temperature 68F, ECTS resistance 2.1 - 2.9 Kohms
Engine coolant temperature 194F, ECTS resistance 0.24 - 0.26 Kohms
(Roughly a factor of ten difference.)