[msquaredF33]

My 435i has a rough idle and misfire which I can’t seem to fix. Today I made an interesting discovery for which I seek this group’s input. The idle smoothes out if I simply unplug the MAF sensor! I’ve been driving with MAF unplugged for a day now and if I didn’t know better I’d call this totally fixed. Any ideas what I should try next? Here is a video demonstration of the symptom, and the “fix”

https://www.dropbox.com/s/afzt8ihjsu...%20PM.mov?dl=0


Quick history: car has 85K miles and was running perfect but leaking oil (of course!). So I spent 2 days doing all the engine maintenance: new valve cover and gaskets; new spark plugs; new oil filter housing gaskets and fasteners; new serpentine belt; walnut blasted intake valves. Upon finishing all that work, engine fired right up. But this rough idle started happening right away. Using ISTA-D, I have “reset adaptations” a couple times. I also pulled the plugs and checked the gap. Getting error codes 140010, 140002, 140102, etc in ISTA.

[bdragon46]

What tune if any are you running?

[msquaredF33]

Car is stock. No tune! Yet.

Once I get the idle resolved, I will go with Bootmod3

[bdragon46]

Ok. With JB4, they actually recommend it. No limp mode with it unplugged?

[msquaredF33]

I am not getting the usual dire messages on Kombi that would signify limp mode.

[msquaredF33]

Update (and bump for help!)
I’ve been driving all week with the MAF unplugged and the idle has been smooth as silk. Any ideas bimmerpost?

[bheng89]

have you tried cleaning the MAF?

[Tchao]

Hmmm can be a "vacuum" leak with the valve cover project.
The turbo maybe pulling air other than from the MAF, causing issues.

Check all the intake connections to the Valve Cover, like the PCV system.
Your car is made to incorporate MAF readings in its calculations.

Also check the entire intake system since you also did a walnut blast, there maybe leaks there too.

[amw896]

how were the intake valves after 85k and on what oil and interval? Just curious because I thought this was mostly an n54 issue

[Gospeedracer]

I'm interested in hearing about the intake valves state at 85k on an n55. Any pics from the overhaul?

[F30ed]

Q: how did the internals look when you opened it? Any rust on VANOS?

You mentioned you replaced the cover. Why? Any chance new cover is defective and leaks air in PCV system?

[Poochie]

Originally Posted by msquaredF33

I am not getting the usual dire messages on Kombi that would signify limp mode.

But the check engine brightly light. That's the general message that the car is in limp mode.

[harkes]

msquaredF33
I have been driving with the MAF unlugged for the last four years. As stated above I also started doing this with JB4 and now that the JB4 is retired I continue with MHD where I have had my tuner program the MAF out.
When the MAF signal is gone the DME default to Alpha N (I believe). Which does not care about your intake. Win-win

[harkes]

Originally Posted by Poochie

But the check engine brightly light. That's the general message that the car is in limp mode.

This is simply not correct. The CEL is exactly what it is an abbreviation for Check Engine (Light). Something is wrong - usually minor stuff or a temporary hiccup. Car will usually continue to drive like normal.

[bradsm87]

Reset adaptations?

[msquaredF33]

Originally Posted by Tchao

Hmmm can be a "vacuum" leak with the valve cover project.
The turbo maybe pulling air other than from the MAF, causing issues.

Check all the intake connections to the Valve Cover, like the PCV system.
Your car is made to incorporate MAF readings in its calculations.

Also check the entire intake system since you also did a walnut blast, there maybe leaks there too.

I’ve checked and it appears everything is tight and properly sealed. I need to buy a smoke machine to do a more thorough vacuum leak test.

[msquaredF33]

Originally Posted by Gospeedracer

I'm interested in hearing about the intake valves state at 85k on an n55. Any pics from the overhaul?

To be honest the valves didn’t look too bad. Not sure that I would have gone to the trouble, but definitely the walnut blast got everything all nice and clean!!

Before


After

[msquaredF33]

Originally Posted by F30ed

Q: how did the internals look when you opened it? Any rust on VANOS?

You mentioned you replaced the cover. Why? Any chance new cover is defective and leaks air in PCV system?

I did not look too closely at the VANOS but everything else under the valve cover looked great and I had not been having any drivability issues. I replaced the whole valve cover because I was doing the gasket anyway (major oil leak) and I was hearing that “squeal” at low RPMs which indicates a failing PCV valve. And as we all know the PCV is integrated into the valve cover.

I suppose there is a possibility the new cover is defective. I’d not considered that. Thanks for the idea, will explore this one.

[msquaredF33]

Originally Posted by bradsm87

Reset adaptations?

Per my original post, I had already done that a couple times

[F30ed]

msquaredF33, another idea - since you removed/installed intake manifold, air leak can be somewhere in that area, anywhere after MAF sensor. Misfire can be due to lean mixture at low RPM, fuel/air ratio is so low that it can not ignite sometimes. When the engine warms up, fuel injection at idle drops to minimum, that is when it becomes very sensitive to any air leaks. Again, just an idea...

[Mr_SDP]

Hey @msquaredF33 did you figure out or resolve your issue?

I’m having the same thing happen to me after I replaced the oil cooler/oil filter housing gaskets. I did have to move intake manifold back to get to gain access to one of the oil filter housing bolts (as is the case with anyone who does this job). After putting everything back together it fired right up and ran perfectly for 5 mins. I turned it off for an hour or so. Then when I started it back up rough idle and CEL occurred. So if you fixed your issue I’d REALLY like to know what the fix was. Thanks man!

[Mr_SDP]

Originally Posted by F30ed

msquaredF33, another idea - since you removed/installed intake manifold, air leak can be somewhere in that area, anywhere after MAF sensor. Misfire can be due to lean mixture at low RPM, fuel/air ratio is so low that it can not ignite sometimes. When the engine warms up, fuel injection at idle drops to minimum, that is when it becomes very sensitive to any air leaks. Again, just an idea...

Hey F30ed is it common that removing/installing the intake manifold can cause an air leak? I torqued mine back to the specs but am having the same issue as the guy who started this post....