Running rich and rough idle when engine is warm

Overlord475 · 23rd July 2010, 20:53

Hey guys,

Recently bought my 1st M5 and it's in great shape. But it does seem to be running a little rich and after it's warmed up it idles rough when stopped.

The running rich might have to do with the fact the OP had the cat removed and installed a 3" ss pipe back from the headers. Idk if this is confusing the fuel o2 mixture? It does still have an o2 sensor.

The rough idle only seems to happen after I've been driving a bit and the car has warmed up. It does seem to clear up a bit when some load is put on the engine like the A/C. Accelerates fine and doesn't seem to have any weak spots in the power band other wise. Don't know if this is common of the E34.

One more thing, there's a really weird rotational clicking noise coming from what seems to be the e-brake. It's only heard when the car is moving and increases and decreases with the speed of the car (not the RPM's). It seems to clear up slightly when the e-brake handle is pulled a little. Or it changes pitches anyway. You can feel the vibration in the e-brake handle. I was under the car yesterday looking for any thing loose and couldn't find a thing. I did tighten up the e-brake but the click is still there.

Any ideas???

Thanks for the help!

mottati · 23rd July 2010, 23:03

a rough idle when warm is pretty normal for an s38. That said, there are many factors that can make it worse/better. THere are a ton of vacuum hoses under the plenum, they are probably dry rotted and leaking, causing multiple vacuum leaks. Replace them all and your car will run better, and you may potentially save your engine from running lean and burning a valve. Fuel injectors are probably also ready for service. There are companies where you can send out your injectors for cleaning, and they will make sure they all flow consistant volume, look for a recent thread about replacing the injectors. There's also a recent thread about ballancing the throttle bodies, which will help smooth out the idle a bit.

What makes you think it's running rich? A de-catted S38 is very smelly! The O2 sensor is upstream of the cat, so not having a cat will have no influence on o2 sensor readings, if the chip is stock, it could actually run a little lean. If the chip has been replaced, for a de-cat pipe, that will usually program it to run a little richer to compensate for the freeer flowing exhaust.

Overlord475 · 24th July 2010, 22:17

I can smell that it's rich and the mpg seem low. I'm only getting about 65miles per 1/4 of a tank.

The car does have a Dinan chip it.

Thanks for the advice on the rough idle! I'll def look into those vacuum hoses and the tb's