Crappy gas mileage/Dipping Idle

[justjuiceit]

I got my 1993 240SX in April and I was amazed with getting over 30 mpg (with 87 octane) with mainly highway, but some city driving too. Recently the mileage has been in the lower 20s. I changed the oil, air filter, sparkplugs(NGK) and the wires in hopes this would help, but it didnt. One thing I did notice when my gas mileage started getting bad was when I came to a stop with the clutch engaged(shifter in neutral), the rpms would dip below 500 rpms, then go up to about 600. Sometimes I would tap the gas so it would idle at 700 rpms. With the a/c on it didnt dip the rpms at all, but recently it has been dipping to about 700 rpms with the a/c on while it usually idles at 1000 rpms. I probably should check the engine for codes, but the check engine light burned out, is there an easy fix for that? Any ideas for what the problem may be? Thanks for any help.

[tonkajuris]

Check your IACV Valve, it is stuck open. Take it off and blow it out with carb cleaner. Should fix it immediately.

[pimpingurz]

i'm having a similar problem w/ my J30 93. Bad gas mileage and idle keeps going so low that the car shuts off. where is that valve located on the J30?

[hamsterball]

on the KA24's it is located around the intake manifold (kind of like under it)..

it might be in the same location for you as well..

hopefully.

good luck.