Weird 318is rich idle.

[M42Power]

So, my 318is has this weird idle issue.

The car runs extremely well, and it idles rock solid for most of the time.

But when the car is warmed up it idles rich, it failed co emissions at idle. The idle is stable, it doesnt go up and down all the time, it only stumbles occasionally when you accelerate off idle.

As soon as it goes off idle, it burns well. If you hold the idle a little bit higher with the throttle, it doesn't burn rich anymore.

So what could this problem be? I have done the mess behind the intake previously, so i dont think there are any vacuum leaks.



For extra clarification, my car has a cat but no o2 sensor. When i scanned the VIN, it had an option that was ''prepared for leaded fuel'', so that means that it controls the idle mixture via the CO screw on the afm, right?

[Dj Buttchug]

im pretty sure it should have a working o2 sensor. Do you mean it has an o2 but not a cat?

[M42Power]

im pretty sure it should have a working o2 sensor. Do you mean it has an o2 but not a cat?

Nope, my e30 has a cat but does not have an o2 sensor. It came this way from the factory.

[roguetoaster]

So, my 318is has this weird idle issue.

The car runs extremely well, and it idles rock solid for most of the time.

But when the car is warmed up it idles rich, it failed co emissions at idle. The idle is stable, it doesnt go up and down all the time, it only stumbles occasionally when you accelerate off idle.

As soon as it goes off idle, it burns well. If you hold the idle a little bit higher with the throttle, it doesn't burn rich anymore.

So what could this problem be? I have done the mess behind the intake previously, so i dont think there are any vacuum leaks.



For extra clarification, my car has a cat but no o2 sensor. When i scanned the VIN, it had an option that was ''prepared for leaded fuel'', so that means that it controls the idle mixture via the CO screw on the afm, right?

What an odd option. If it were prepared for leaded fuel it would probably not have a cat from the factory as I believe leaded gas destroys the cat substrate. What is the status of the little wire on top of the harness pack under that black cover on the firewall?

I would suggest that if the car is not passing at idle, but may pass off idle that you just raise the idle for the test via the throttle screw. Other options/ideas would be to check your plugs, replace the catalytic converter and add a different pipe or an O2 sensor bung so you can use the O2 sensor as part of the system.

One other thought, does the car show any codes via the stomp test? Reason I ask is that the throttle position sensor in my car caused a similar off idle bobble and rich idling, and if the car will not throw a code you know you have a TPS issue.

[brads2002]

Coolant temp sensor will cause them to run rich but it usually triggers a cel. I am not sure if you have a cel though being a euro. My m3 doesn't but has an o2 and cat.

[M42Power]

I already replaced the coolant temp sensor a while ago.

The little wire is connected as it should (no 02 sensor)

I thought of adding an o2 sensor but i think i need a different ecu for that.

Haven't thought of the tps sensor tough, i have no way of doing a stomp test since i have no CEL (But i can wire in a new one)