Check engine light on at idle

[Coupenut]

I'm hoping for some advice from the collective wisdom of the group rearding an issue that I'm having with my car.
The car is an 88 325iX, 175K miles, manual transmission.
When the car idles for example at a traffic light after a few moments the check engine light comes on. If I press the accelerator and raise the engine RPMs above approximately 1500 the light goes off. This doesn't happen when the car is moving and only after it reaches operating temperature.
Does anyone have any thoughts about what might be causing this?

Thanks,

James

[jlevie]

Intake leaks and/or an aged O2 sensor (replacement interval for the sensor is 100k). A smoke test will find any intake leaks.

[e30topdown]

^+1
What Jim said. If the O2 sensor hasn't been replaced in a long while, you might want to do that anyway. I usually replace at 60k miles.

[mazzo]

Any stomp test code?

[cavpilot]

Definately an intake vacuum line. Be sure to check the vacuum line on the underside of the throttle body. That one gave be the exact same indications.

[jayamasaki79]

what is the BOSCH O2 sensor part # ?