At my wits end Bad Idle M42
 

Initially I had a high idle. I'd take that high idle back now.

After changing numerous vacuum hoses and ICV the idle was normal but still poor gas mileage. But drivable.

I go away a couple months ago for a weekend and come to a rough idle after warming up. Random CEL.

I initially made my own hoses from the ICV - tree - fuel injectors.
Thinking maybe one hose fell off I replaced the set with a factory set.
Same problem.

Replaced 02 sensor.
Same problem.

Next I'm replacing the fuel filter only because it's probably never been changed.

Car also sounds like a diesel at idle once warm.
It's barely drivable at this point.

I've spent $1000 in parts replacing broken plastic parts.
I still have suspension to go.

If I can't get this working soon it's leaving my driveway.
Either to a buyer or to a junk yard.

Reading more thread.

throttle body heater?
Cam sensor?

Have to ask, have you pulled the AFM to TB hose (The big one) and checked it for cracks.. OFF the car. ??

IAV hoses.. I just had to replace bothof the 3/4" hoses on mine they were splitting..


IAV - Checked..

Has to be air getting in there somehow..

I've changed the TB hose.
IAV?

Decided to scan the codes again.

2A Knock sensor, Cyl 3-4
46 Oxy sensor

Changed the 02 Sensor tonight.
Guess time to look into the knock sensor.

Odd though.
The last time I checked for codes I got
C9 Emission (lambda) control

Have you considered a clogged cat?

Ed,
How much for a knock sensor 12141734580?
PM me the price.

From what I'm reading it's a 3 HOUR PITA job IF nothing breaks.

It sounds like it's clogged. How could I tell?
Car sounds like a diesel.

This does not look like a job I want to do. :(

Can a clogged cat cause a knock sensor fault?

Try removing the O2 sensor and starting it. If things improve I would say you have your issue found.

I would hold off on the knock sensors for now. That said, the best way to change the sensors is to remove the oil filter housing. That gives you access to both sensors without removing the intake manifold.

https://www.facebook.com/BimmerBum/p...type=3&theater

M42 has just one sensor. What am I looking for?

The whole oil filter housing?
That sucks. I already replaced the bushings and gasket. Then I need to remove the alternator and loosen the belts too?
I've taken the upper intake manifold off so many times now, I can do it in my sleep.

Looking at the motor from the front I see 2 sensors with clips on the right side. Are those the knock sensors? Looks like I can get my hands right in there.

Has anyone here replaced M42 knock sensors?
Maybe they are easier than M44 and I6 sensors?

Didn't realize the photo was of the sensors. I'll take another look tomorrow. Thanks.

I edited the post to say sensor instead of sensors.

You are correct, there is only one O2 sensor on the M42. It is before the cat. If the cat is clogged then removing the sensor will allow some exhaust to escape (rather than trying to find its way though the clogged cat), idle, etc should improve but it won't be perfect with the new hole in the exhaust and O2 sensor not doing its job. You are looking for improvement over the current symptoms. This is not a solution and this is not a way to drive the car, this is just for diagnostic purposes.

You can come at the knock sensors by removing the intake manifold (upper and lower) but you can also get to them by removing the oil filter housing etc. Personally, I would rather go the oil filter housing route. That is how I did them on my Club Sport.

Like mass air meter codes, knock sensor codes are often just a symptom and not the actual problem.

I have no idea what can cause rough idle and poor gas mileage.:biggrin:
Can I pick it up instead of sending it to the junkyard?

I knew sensors was a mistake. :) I was tired when I posted.
Since I already have taken apart the oil filter housing to replace the gasket, that shouldn't be so bad. The alternator is a bitch though.

I'll pull the 02 sensor. That was practically welded on. After 5 minutes my idle drops.
It all seems heat related.

I'll keep that in mind. :)

Confused. You pulled the o2 sensor or you will pull the o2 sensor?

I WILL remove the sensor. Haven't messed with it today yet.
Do I also disconnect?

02 sensor on an M42 is soooo much easier than my M52. :)

Added: Found a cool video on checking cats.