Bad idle,running rich

[98birdls1]

So I recently bought a 95 240sx w/ 150,000 miles. I drove it back 400 miles from Georgia and it did great. Gas mileage was a little low though.

A week or so ago it started acting up. Cold idle is around 1200 which seems to be normal. But when the motor gets good and warm, the idle drops to a little below 600, which is on the outskirts of normal, and it will run a little rough. But about every 4-5 minutes (with the a/c off) the idle will jump to 1000rpms and hold there for a minute or two then drop back down to 400ish for a second before coming to rest at 600ish. It almost stalls when this happens and has been getting worse. When this happens and I try to acceleate the car stumbles and falls till it reaches 2500+rpm and it then acts fine.

Now, when I'm crusing at say 3000rpms, when I engage the clutch and shift to neutral and lift off the throttle the exhaust will pop and crack like it is running very rich. And I've been getting about 20mpg.

What could some of the things that would cause the symptoms? I don't want to tear into the motor becuase it won't be in it but for a few more months but this idle/stumble thing is annoying. Thanks in advanced.

Luke

[Aries]

possibly the idle air control valve is bad.could also be a bad fuel pressure regulator.

or even an O2 sensor.

Do this, check the voltage on your O2 sensor, and try idleing the car, and unplugging the vaccuume line on the fuel pressure regulator. Then come report your findings and we'll be able to help you more.

[InsanityInc]

Most likely something is wrong with either your O2 sensor or your throttle position sensor