E46 running rich

[nonturbodan]

Before I pull this engine out for the 2.8 I'm about to dunk in I'm trying to determine if it is good or not to see if it can be sold as a good used engine or just as scrap/parts. It runs well, no check engine light, no oil consumption and good fuel economy. The only symptoms of a problem are a tendency for the engine idle speed to dip as revs drop back to idle and a rich smell from the exhaust. The idle will also dip as the ac compressor cycles on or if a sudden load is placed on the electrical system. Basically it has a weak idle. Runs smooth other than when the idle is dipping and recovering, no loss of power. Feels strong for an M54B25.

The car is high mileage and I have been going through maintenance items. Its got a new crank vent valve and hoses, new Bosch pre-cat oxygen sensors, new Kayser fuel filter with pressure regulator, new intake gaskets, new intake boots, new vac lines and caps, a clean and lubricated ICV, a repaired DISA valve and new plugs. There is no reason for it to be running rich but it sure is. I am concerned that there is wear on the intake valves and seats resulting in low intake manifold vacuum and elevated cylinder leakage. I will do a leakdown test at my next opportunity but I don't have compressed air at home.

Are there any other possible failures that can result in the rich condition, other than the parts I have already replaced during maintenance? The fuel pressure is good, any intake leaks would result in a lean condition rather than rich, and that intake is sealed up tight anyway. Can the secondary air valve cause this?

[dworthy]

Any codes, or the MIL/Check engine light on?

A vacuum can cause a rich condition, as the oxygen sensors tell the DME it is running lean, it will bounce to rich.

How does the MAF look? Has it been cleaned/tested lately?

As for the idle dip, that can be cause be the alternator getting old. What I mean by that is pull out the voltage regulator and check the contact to see how long they are. <- Just make sure you disconnect the battery first

[nonturbodan]

No check engine light. DME seems to think everything is great.

The MAF has been cleaned and swapped with a spare. Problem is still occurring with it disconnected as well.

I did have a neat little plug in scan tool that would show adaptations and live data. It was borrowed and has not returned. That would be nice to have.

The alternator does appear to be original at 190k miles. Might be a good idea to replace it too as a maintenance item.

One thing I wonder about is long term adaptations. This thing came to me with the intake air boot about halfway off of the ICV. Big time air leak. Been like that for a very long time. Years by the looks of the boot and the amount of grit in the intake. Despite this the car ran fairly well. Since repairing all of the vacuum leaks I've put about 600 miles on it and the rich condition remains. I may need to reset the adaptations and let it start fresh because it still seems to be compensating for the air leak. It also seems as though these adaptations, among other things, are stored in non-volatile memory because this thing has been completely dead for days at a time and had the cables touched together and it has not even lost radio presets.

[dworthy]

The adaptations will adjust over time, but BMW recommends whenever you replace major items like oxygens sensors to reset the adaptations.

After the winter car hit 170k miles the brushes were worn down, and I had the luck to find a new rebuilt alternator in the junkyard, but if you do replace it, make sure it is in a Bosch reman in a black box.