Z3 engine while idle surges

My Z3 when stopped seems to be surging and when the headlights are on they cut in and out when this happens. Any ideas? I just replaced the water pump and thermostat.
Thanks for the help.

Originally Posted by jrblanks

My Z3 when stopped seems to be surging and when the headlights are on they cut in and out when this happens. Any ideas? I just replaced the water pump and thermostat.
Thanks for the help.

Simple thing to check is your gas tank cap seal. If the seal is worn out it will lead to surging during idle.

Okay, thanks. I will purchase a new gas cap today.

The cap will be expensive; the seal can be replaced separately (~$6).

Do you know if I can purchase the seal at a local part store like AutoZone or is it a item that has to be bought from BMW?

I recommend the local dealership. Should be an in-stock item. Make sure you have the OEM cap, if not the seal (OEM) might not be compatible.

Okay, thanks.

I'm having a similar issue but only at start up when cold. After car warms up surging goes way. My first thought is the car needs a robust tune up... plugs, fuel filter, air filter already changed. No codes showing up. Just thinking out load but have you tried pulling codes and is maintenance up to date?