# '90 240sx Fluctuating Idle



## Svenny (May 18, 2013)

Hey Guys,
Just bought my second 240sx! W00t! Had to leave my first one in my hometown when I moved. But anyway, just got my 1990 240sx 5 speed and it seems to idle weird or maybe it's just me. When stopped and in neutral it seems to range between 500ish to 1000rpm. The needle just moves up and down, sometimes it will stay for a second or two before moving again... is this a PCV issue or what? Any help would be greatly appreciated.

-Svenny


----------



## smj999smj (Jan 1, 2006)

Sounds like it's running lean by your description. Have you checked for vacuum leaks, codes, etc.? KA24E's did have the occasional intake manifold gasket failure or sticking EGR valves. Another issue that used to happen on the 240SX was the bracket on the exhaust manifold that keeps the O2 sensor wire off of the heat shield would break and the wire would burn-up on the heat shield.


----------



## rogoman (Dec 16, 2004)

Two things to check:
- The IACV may be dirty. Remove it, take it apart and clean the carbon out. Check the solenoid to make sure it's operating.
- The MAF harness connector pins may have oxidation on them. Clean them with emery cloth, apply dielectric lube.


----------



## Svenny (May 18, 2013)

*Thank you!*

Thank you both for your tips but I am a bit inexperienced when it comes to auto repair. Could you tell me or point me to instructions on checking/cleaning the IACV or how to check for Vacuum leaks or how to check for MAF harness pins for oxidation? Thank you!


----------



## rogoman (Dec 16, 2004)

Like I said earlier, the IACV can be removed and cleaned. On the 240SX it's a PITA to remove/install the IACV because of it's location. The starter needs to be removed to get full access. There are two electrical harness connectors that first need to be unplugged; be careful with the locking spring clips.

The MAF harness connector also has a spring clip so be careful when removing it. Once the connector is opened, just look at the pins for any powdery residue. They can be cleaned gently with emery cloth, just don't overdo it. When reassembling, use some dielectric lube on the pins.

To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. A good place to connect to is the charcoal canister. There should be three hoses connecting the carbon canister. Two of the hoses go to a purge valve that's built into the canister. The second larger hose off the purge valve should be your vacuum line. With the motor fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be 21 InHg.

If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.


----------

