We have a S430 and when she starts up she runs very rich (smell). What module /part controls the Air/Fuel ratio?

Thanks,
Erik

There is no one module or part that controls this.

When the car is cold (below about 150 degrees of coolant temp), the engine control unit runs of pre-programmed fuel and timing curves (open loop). As you know, the car needs to run more rich when the engine is cold. Once the coolant temp hits that pre-set level, it switches over to closed loop, which starts to read from the MAF and the oxygen sensors in order to actively adjust the a/f ratio to get as close to stoich as it can.

If your car runs overly rich, it should throw obdII codes. If it doesn't, its likely operating as expected.

It has been throwing CEL's - been like that for a while now. We've replaced the part that it was complaining about 3 times, with no luck. Now, when the car is hot - she won't start.

Drove her to the local mechanic - awaiting his diagnosis.

Thank you,
Erik

what codes is it throwing?