E34 540i Rough Idle Check Engine Light

[e34lives]

I have a 1995 540i automatic with 194,600 miles

I am a bit stumped. Rough idle occurs at stop light with car in Drive (idle 600rpm), triggering a check engine light with the following fault code 1222 - O2 lean/rich control stop, 1221 - O2 Sensor 1 and 1213 - O2 Sensor 2 lean/rich control stop. The car drives well at higher rpm, but this rough idle re-occurs after repeated resetting. Check engine light would sometimes go away after driving at higher rpm as well. Not sure if this is related, but also experiencing stalling during cold start when I engage into Drive, and requires warm up of 2 – 3 + minutes in Park before shifting into Drive without stalling, but this only occurs 60% of the time.

Replaced Following Items With No Resolve:

Bosch O2 Sensor (both of them)
PVC Plate & Gaskets for PVC + Throttle
Hoses Going To PVC and Throttle
Intake Manifold Gaskets
Head Cover Gasket
Mass Air Flow
Throttle Control (both of them)
Throttle Position Sensor
Engine Crank Sensor
Spark Plugs
Coils
Idle Control Unit
Engine Temperature Sensor
Fuel Pressure Regulator
Oil Filter & Pan Gasket
Transmission Fluid Filter & Gasket
Fuel Pump Relay
Fuel Filter
Air Filter

I have cleaned throttle unit with lots of carburetor cleaner and a rag. I have checked for leaks by spraying throttle cleaner throughout engine intake areas looking for potential leaks but found none. I also put in I gallon Lacquer Cleaner to ½ tank of gas and run hard to clean out the CAT. Clean off the injector tips free of oil crud and tested with EFI electronic injector tester to make sure they were working ok. I checked coils with EFI electronic coil tester to make sure they were also working ok. I put in one bottle AT205 reseal into engine oil.

Not sure what to do or check next to address this issue, any suggestions is appreciated.

[E39 Expert]

With 194k on the clock i would take the fuel pump into consideration. With all the symptoms you are having i would defiantly perform a fuel pressure test right away. Fuel Pumps don't stop working right away they take a little while to stop working all together. Your specific vehicle should have between 46-54 psi of fuel pressure (according to ALL DATA). The shrader valve test port is located on the fuel rail once you remove the engine cover. Since the engine has to warm up 2-3 min before driving away means that you have low fuel pressure. Cars use a lot more gas when cold than when war.

[e34lives]

Thanks for pointing out the fuel pump as possible cause of the rough idle and stall. I had a new fuel pump replaced about 9 years ago, it now has 30K miles on it. My previous fuel pump lasted 134K miles / 11 years. So maybe it is time to replace.

I will look into checking out the fuel pump, as I have had the car sit for six month at a time in the last ten years the pump might have experience some rust from air exposure, since I usually do not have a full tank when putting car in storage.

[e34lives]

I was reading further about rough idle at lower rpms and went ahead and double check again the intake ducts in the MAF area for any splits or damage and found none.

I also remember a discussion on the oil cap seal and decided to take a closer look, the rubber on the cap is still good but I notice that the tightness of the cap was not as firm as I recall in the past, so I decided to give the wings a gentle bend to make it more snug.

I also took another look at the PVC area and all the two plugs that cover the hole and I rotated the one with the L shape to see if there was any give, this is a new PVC Cover, and assume it was in good working order. I was concern that the L shape plug could rotate so easily. But everything looked tight and Carburetor cleaner leak test did not indicate leak.

[e34lives]

I replace the oil cap with a new one. No change, rough idle still appears. I been reviewing my options and the best approach is to do a smoke test to identify where leaks are located within the engine, since my efforts with carburetor cleaner did not turn up an obvious leak, so it might be a smaller leak. I ordered a smoke machine and will give that a try once it arrives.

Just a note, been pull 1222, 1221, 1212, 1213 codes, but not every time, and get a combination of the 2 , 3 or 4. But every time it occurs is during idle with engine in Drive with breaks on peddle. The Check engine light does sometime go away when I drive the car a bit, or drive it aggressively, otherwise I will do a stomp test and then do a clear codes to reset.

[marshallnoise]

I know, necrobump. But its for a reason.

I am having the same issue with my car. I just went through and replaced the catalytic converters hoping it wasn't a clogged cat.

Now, the biggest difference is that my brakes are absolute crap and have been. So much so that I decided to replace the entire brake system and pump through brand new fluid. Took the car out for a test ride and the same check engine lights fired up and by brakes have zero boost and I get that crazy rough idle. Car runs fine just over 1,000 RPM. Brakes still stuck at any RPM.

So I am beginning to think that I have a massive vacuum leak at, near, or in the brake booster. I am going to block off the brake booster from the vacuum system and see if that clears things up first. I will report back when I figure more out.

[marshallnoise]

I have three places to check for vacuum leaks.

1. Right at the throttle body source of the brake booster line
2. The vacuum line itself
3. The booster

I took off the line going to the booster, threw a bolt into the rubber line at the throttle body and went for a hairy drive with absolutely zero brake boost. Check engine lights are gone, engine idles fine and runs generally great!

Then I examined the line that has a check valve on one end. Sure as poop, the plastic that makes up some of the hose on both ends is not air tight at all.

Transmission and Brakes by Paul Abbott, on Flickr

Transmission and Brakes by Paul Abbott, on Flickr

Transmission and Brakes by Paul Abbott, on Flickr

Moreover, the damned thing crumbled.
Transmission and Brakes by Paul Abbott, on Flickr

Transmission and Brakes by Paul Abbott, on Flickr

Next step is to replace that line with something else. Check valve is good BTW.

[Billyj]

I wonder if that has something to do with my 'lean beyond compensation' codes haha
No one pays me to fix my own car so I usually just load the part cannon and fire away

[marshallnoise]

LOL, "load the part cannon and fire away." That is really funny.

But I think this is the problem. I am going to epoxy around the check valve though and make sure it is sealed up before reinstalling it.

[marshallnoise]

Ok, new vacuum line (actual vacuum line, not fuel line) and its a slight improvement but largely non-existent brake boost. The good news is that the check engine lights are gone and the idle shifting up and down is gone.

Now, I did the fast-pump-brake-at-idle thing and the idle did shift just slightly and one time the check engine light came on and then went off right away.

I tried to do the smoke test and that was just stupid hard. So I am back to the drawing board.

Might it be something as simple as the master cylinder needing to be gone over?+

EDIT:
So I went back out to the car and did the typical master cylinder test. Pumped the brakes until firm, turned on the car, the pedal went soft then firmed up about a half inch or so farther down. Sounds like the Master Cylinder is ok.

Then I noticed something when I was putting pressure on the brake pedal; it really sucked the engine rpm down and when I let off, the rpm rose a bit.

Booster with pinhole leaks?

https://www.youtube.com/watch?v=ZXTfWK06ctk

Just saw this. The idle doesn't surge that badly, but it definitely drops a bit.

[marshallnoise]

I am throwing parts at the bitch now. LOL.

I replaced the master cylinder and re-bled the system two more times. I also replaced the front throttle body gasket because it was old and tired and it was loose on the bottom bolt anyway.

The engine is running better. But, my symptoms are exactly the same as before and the check engine lights come on when at idle and pumping the brakes.

I can't find any new boosters available so I ordered one up on eBay used and the junkyard has another one from a 740i so I will get it too.

I will report back.

[Sir Montalbon]

I've been having a similar issue with my 211k mile 540i and after going through a lot of the same parts and diagnosis. I'm starting to look at the brake booster as well. Keep us updated.

[marshallnoise]

I've been having a similar issue with my 211k mile 540i and after going through a lot of the same parts and diagnosis. I'm starting to look at the brake booster as well. Keep us updated.

I will.

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[Mykk]

Use a 3/8"s steel fuel line, cut off the ends and bend line to snake around behind engine, follow the fender and to the brake booster only using short pieces of rubber line at engine and booster side.

Brake booster will have an effect on idle characteristics, it's a big demand on manifold vacuum to depress brakes and loss of manifold vacuum at idle means rpm dip, lean condition.

[marshallnoise]

Use a 3/8"s steel fuel line, cut off the ends and bend line to snake around behind engine, follow the fender and to the brake booster only using short pieces of rubber line at engine and booster side.

Brake booster will have an effect on idle characteristics, it's a big demand on manifold vacuum to depress brakes and loss of manifold vacuum at idle means rpm dip, lean condition.

Yeah, that is why it is suggested to pump the brakes rapidly while,parked at idle and see if you can induce a vacuum leak, engine code trigger and eventual engine stumble.

I personally had some leaking at the back of the master cylinder but it looked hydraulic opposed to vacuum so I replaced it anyway hoping it to be the issue.

The booster is the last point of failure and last component I have to replace at this point.

It is a difficult diagnosis until you equate the check engine lights with poor braking/manual braking performance. I have not 100% confirmed, yet...

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[Billyj]

Here's a video of me pumping the brake at idle and AFR readout.
After a short warmup to operating temp.

Turn volume down I forgot I had music playing haha
https://youtu.be/zo41nP7JlMA

[marshallnoise]

Yeah, that has got to be the brake booster. Unless your gasket between the master cylinder and booster is bad...but mine looked fine when I replaced it.

[marshallnoise]

I can finally put this mystery to rest! I just went to the junk yard and pulled a booster of a 95 740i and swapped it in to my car. Sweet baby Jesus, I have brake boost, no check engine lights, and a nice straight idle!

I accidentally punched the new check valve grommet INTO my old booster so I had to tear it apart. What I found was that the diaphragm that is closest to the brake pedal (opposite side of master cylinder) was fine. The other diaphragm that was located right after the master cylinder was super squishy and ultimately brittle. I looked around and sure enough there was a tear about a half inch long that must have been the source of the leak. Now, I stuck my finger in it and it tore some more, VERY easily. And eventually the tear went all the way around. The front diaphragm felt different than the rear one and I am betting that a leaking master cylinder sprayed a decent amount of brake fluid into the diaphragm and weakened it over time, causing the failure.

[Sir Montalbon]

Congrats on sorting it out! Brake booster is next (last really) on my list. Thanks for the update.

[marshallnoise]

Congrats on sorting it out! Brake booster is next (last really) on my list. Thanks for the update.

You bet. I can say without a doubt, after replacing every brake thing on the car, I completely forgot how great of brakes it has.

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