98 Z3 M44 RPMs dropping when idling - what to look for?

[jimmyfloyd]

I am having an idle issue on a 98 M44. Car was running good, but throwing codes for the cat, so I decided to replace it this weekend, along with a couple other items. So I replaced the following:

• Oil Change
• Fuel Filter
• Both O2 sensors (Bosch)
• Use, but good cat from parts car.

Upon starting the car up, the idle would drop a couple times to around 400-500 rpm, then pop back up to 800-1000. It only does this at idle. When driving, the car has the expected power and no issues. No check engine lights, but I have not had a chance to check for pending ones. Car has only been driven ~10 miles since.

What would be the cause of the RPMs dropping at Idle, and where should I focus?
I am thinking:

• Vacuum leaks
• Check Pending codes
• Check plugs
• ??

Thanks in advance

[Vintage42]

These:

• Vacuum leaks
• Check Pending codes

[jimmyfloyd]

Turns out it cleared itself up. Someone mentioned that the computer could have been still learning the new Sensor values since I had run it a while with the bad sensors.