At my wits end Bad Idle M42

[BimmerBum]

Leaving it plugged in should be fine.

[1996 328ti]

I pulled the O2 sensor out leaving it connected.
Ran the car for maybe 10 minutes.
Idle dropped once but there seems to be a lot of pressure coming out of the sensor hole. Hard to tell what's normal. Hardly anything coming out of the tailpipe.

Rescan the codes and now I have Knock control regulation.

Reinstalled O2 sensor. Cleared codes.
Ran for about 10 minutes and idle started to drop again consistently with the same Knock control regulation fault.

Stuffed cat and maybe not a knock sensor?
Muffler?
Resonator?

Boy the exhaust gets hot quick.
Got a nice little burn on my wrist.

I have a good exhaust shop I can bring it to.
I suppose I can have him remove the cat to inspect and install a straight pipe if it's bad until I replace the cat.

[BimmerBum]

Originally Posted by 1996 328ti

I have a good exhaust shop I can bring it to.
I suppose I can have him remove the cat to inspect and install a straight pipe if it's bad until I replace the cat.

That would be my plan. Wasn't there some issue with the 318ti cats from the factory? Didn't BMW replace a bunch of them for free?

[1996 328ti]

Originally Posted by BimmerBum

That would be my plan. Wasn't there some issue with the 318ti cats from the factory? Didn't BMW replace a bunch of them for free?

I think 98 had bad cats.
We have no emissions or inspection in SC so I have time.

Tomorrow I'll replace your fuel filter and run the car without the sensor for 20 minutes as a comparison.

It's OK that the O2 sensor gets hot without any air moving around it?

[BimmerBum]

Originally Posted by 1996 328ti

I think 98 had bad cats.

It's OK that the O2 sensor gets hot without any air moving around it?

It should be fine. Sounds like you might be getting to the problem finally.

[1996 328ti]

Yep, getting close.

I read a few threads on cats and they all sound like the problem I'm having, other than the knock sensor faults.

I don't regret the work I've already done.
It needed it all. The fuel filter probably has probably never been changed.

[pdxmotorhead]

Always replace the cat and the O2 together.. its really really rare for the O2 to survive a clogged cat...

BTW you can feed a bore scope through the O2 sensor hole and see in the head end of the cat, if its not a clean tidy honeycomb structure,, bad cat.. Or just drop the headpipe and look down it..

The knock sensors trigger because with a plugged cat your overheating the mix in the cylinder and its likely detonating/pinging very lightly all the time.

My 95 throws o2 sensor check lights if the moon is full .. lOL

[1996 328ti]

Last bit of advice I've been given is to disconnect the MAF but I'm going with a clogged cat.

[1996 328ti]

Decided to replace the fuel filter.
It was filthy.

Ran the car for 10 minutes with the O2 sensor until it stalled.
Seemed to run longer than previously but could have been my imagination.

Next I'll see if I can run the car more than 10 minutes without the O2 sensor.
Then with.

That will be my final determination whether it's the cat.

[BimmerBum]

Originally Posted by 1996 328ti

Decided to replace the fuel filter.
It was filthy.

Ran the car for 10 minutes with the O2 sensor until it stalled.
Seemed to run longer than previously but could have been my imagination.

Next I'll see if I can run the car more than 10 minutes without the O2 sensor.
Then with.

That will be my final determination whether it's the cat.

Progress. Perfect.

Fuel filters are so cheap for these things I do mine every 10k. Sometimes it is dirty sometimes not so much. Goes to show what tank of dirty gas can do.

[1996 328ti]

Baffled.
Rough idle and stalls after 10 minutes with O2 sensor.
Remove O2 sensor to allow pressure to escape in case clogged cat.

Now runs for only 3 minutes until rough idle and almost stalls.
Disconnect MAF, idle smooths out. That's almost $500!

From the exhaust fumes, running rich.

[BimmerBum]

Originally Posted by 1996 328ti

Baffled.
Rough idle and stalls after 10 minutes with O2 sensor.
Remove O2 sensor to allow pressure to escape in case clogged cat.

Now runs for only 3 minutes until rough idle and almost stalls.
Disconnect MAF, idle smooths out. That's almost $500!

From the exhaust fumes, running rich.

Did you try it with the O2 screwed in and the maf disconnected?

[1996 328ti]

Originally Posted by BimmerBum

Did you try it with the O2 screwed in and the maf disconnected?

Good thinking.

Installed the O2 sensor.
Ran the motor for 10 minutes with the MAF disconnected.
Idle stumbled a little but not as bad as before.

Cleared fault codes.

Reconnected MAF. Ran for 10 minutes, no problem.
Fuel burning better I guess since the O2 sensor was reconnected.

Rescan codes
Knock control regulation

[1996 328ti]

I can see the first knock sensor past the oil filter housing, but not the 2nd.
I no longer get a knock sensor fault though. ??

[BimmerBum]

With the intermittent knock sensor faults I would say that is not your issue. Also, a knock sensor fault may actually mean there is an engine knock and not that the sensor is bad. But again, I would not worry about that.

So how is the car running at this moment?

I knew it would not run fantastic with the O2 sensor unscrewed the point of that was to see if significant exhaust flow is being blocked by the cat.

I have a spare maf I can send you to see if that solves the issue before you buy a new maf.