Lumpy Idle, Possible Misfire? - Not Solved :'(

[LiftedMuffin]

Greetings fellow ZRoadster folks,

I've been searching around on this and other forums to try and get relevant info - it looked like an issue with the camshaft sensor but having just replaced it the issue is still there. I thought I'd make a direct appeal to the combined wisdom of the forum to see what I should be checking/testing!

This turned into a bit of an essay... sorry!

So the overview:

1999 1.9 Z3 Roadster (M44-B19 engine I believe?). It's at 90k miles and I've put the last ~2,700 on there. I didn't notice any lumpy idle when I got the car and I'm pretty sure it's come on steadily over the last couple of months (~1k miles).

The car starts fine, but when idling it's really lumpy - almost seems to me like there's a frequent but irregular misfire. I sat in it the other day and held it at ~1.5k revs and it still felt like it was missing a beat here and there (much harder to tell than when idling, but noticable). It seems to drive okay though, even if the engine feels a little 'jerky' (technical term) on gear changes up and down. I've not had any issues with it stalling & the lumpy idle seems to improve very slightly when the engine's warm.

I had a "70 - Camshaft Position Sensor" error code showing up. Replaced it with an OEM one from Sopers (can't recommend them highly enough!) - the fault code was gone after going for a run out, and I think it is pulling a bit better at low RPM, but it doesn't seem to have affected the lumpy idle. Feels a bit sluggish under 3k rpm, but I couldn't say with certaintly.

I also got an error code "3E misfiring, sum, relative to exhaust gas" just before I swapped the camshaft sensor but that hasn't come back since the new one went in (will check again after the next drive) and I think was probably due to me removing some of the pipes around the intake to check for vacuum leaks. No misfire codes since so maybe it's not actually a misfire?

Things to note:

• There is a constant buzzing sound coming from the idle control valve when the ignition is on, like somethings shorting inside - stops if I disconnect it
• When replacing the camshaft sensor, I didnt replace (or even clean off ) the metal gaskets between the throttle body outlet and CCV valve/inlet manifold - could they be mis-seated and not sealing properly?
• Probably unrelated but there's a loud rattle from under the middle of the car at ~1k rpm & ~2k rpm which has also developed over the last couple of months.
• I replaced a little vaccum pipe from the fuel rail to the throttle body that was perished, and there is a crack developing in the main air hose after the MAF but I dont think it's gone all the way through. Rest of the air hoses seem to be okay as far as I can tell.

Phew, time for a beer

So, has anyone had anything similar before? Any pointers on what to check/test/replace next? Could it be a coil-pack on the fritz, or the idle control valve? I read that a stuck/broken crank case breather valve can cause a rough idle etc, is it worth checking?

I also read about some Vanos issues which sounded like they had similar symptoms, but I don't think the M44-B19 has Vanos from looknig at some timing chain videos on YouTube - is that correct?

Any help you guys can offer would be really appreciated... I have a feeling it's going to get expensive if I take it in to the shop!

 

[NZ00Z3]

The M44B19 engine has a bit of a rough idle by design. I take it that its got worst over time.

As you have a scanner, have you looked at the fuel trims? High fuel trims on a warm idling engine are an indication of vacuum leaks. Rev the engine to 3,000 rpm for 30 seconds. If the fuel trims reduce, then you do have a vacuum leak. It sound like your car is due for a full rubber boot/hose replacement job. The M44B19 has a number of rubber hoses hidden under the top half of the inlet manifold and the rubber hose from the valve cover to CCV rots out from the inside.

Once you have eliminated vacuum leaks. If the rough idle is still there, then its time for a new and expensive coil pack.

 

[t-tony]

You have to be 100% sure there are no vacuum leaks.

Tony.

 

[Paul Rice]

Could the rattle be the Cat? would this cause bad running @t-tony

 

[colb]

Agree with what the others have said so far, engine must be airtight no splits or cracks in the rubber hoses within the system. Best checked with a smoke machine, it will find the smallest leaks. Bad Mafs don't always set codes so bear that in mind. High fuel trims would indicate an air leak as the exhaust will be picking up on unmeterd air passing through the exhaust making the car think its running lean. To compensate the brain tells the injectors to add more fuel, hence high fuel trims will be seen in live data if you can view them with diagnostics. Bad leaks will add 20% more fuel and reach their max, in doing so the car will have a code set and EML lights up. Sort any leaks, clear the codes then run the engine, have a look at fuel trims if you can, if all air leaks have been eliminated you should see normal lowish readings. they will rise and fall depending on throttle positions.Check c09des again, see if there are any misfires, if there is they should tell you which cylinder is setting them, suspect coils can be moved to another cylinder to see if the misfire follows the suspect coil, if it is the same coil, change it for a replacement and test again using code reader.
Since you changed the camshaft sensor I would assume thats good. To test a Maf try unplugging the electrical connection to it the car will run on default settings, if it runs better then suspect thye Maf, try cleaning it with Maf cleaning spray but don't hold out on that curing a bad Maf, it didn't fix mine. OEM replacement solved my issue when I couldn't find an air leak M43 engine.

 

[t-tony]

Could the rattle be the Cat? would this cause bad running @t-tony

Quite possible Paul, lying next to the car and smacking the cat with your hand should replicate the rattle if the catalyst is broken up.

Tony.

 

[LiftedMuffin]

Thanks for the responses folks! I'll have to give all the hoses a good going over when we get a dry weekend, will see if anywhere nearby can do a smoke test too.

I think the OBD scanner I got can check the fuel trim - I'll have a play around and report back

 

[handsomejackuk]

buzzing idle control valve mine did that @colb noted it... i took it apart and cleaned it a while ago and didnt put it back correctly, I have since taken it apart again and reseated it correctly it dont buzz anymore

rough idle on startup when cold mine does it and quite a lot of the m44 engines are prone to it, there was an ecu software update (rough idle) that should have been done (at Dealers) to cure this but not all cars have been done fresh engine oil can help with this too as sticky valve lifters cause the rough idle too, mine still does it but settles down after a minute, mine does this more in cold weather but not so much when the car is used regularly and never in summer...

maybe we all need to get together and report on ecu software versions on m44 engines, i would love to know what version mine is running...

interesting reading

http://bmwowner.com/forum/viewtopic.php?t=178098

 

[Scooblitz]

Hi @LiftedMuffin . Welcome to the site but sorry to hear about the z troubles. A lot of what your describing sounds familiar with my old m44 and as a lot of members have already pointed out, the m44 has a bit of struggle with idling and emissions.

Have you checked the spark plugs to see if there are any duds in one of the cylinders?

When i ran my m44 it would idle pretty rough to the extent that i thought it was going to cut out so i would rev it at the lights a touch to 1000rpm. It idle at around 600-700 and sputtered fuel out the back exhaust pipe. As i got used to the car, i stopped revving it as it never actually cut out.
I found that running higher octane fuel made the car run much better. Noticeably so. Idled smoother and pulled 5% better too. Worth a try if you are not already fueling with 98+.
My idle control valve also gave off a buzzing sound on ignition but i saw from its history it had been replaced before so never went down the route of replacing.

 

[handsomejackuk]

also you will notice with m44 maybe on other models too that idle drops when the car comes to a complete stop..

i.e. If you coast in neutral idle will be up to 1000rpm once the ecu senses the car has come to a complete stop, the idle will drop apparently this was a fuel saving thing.. some ecu's may have had this written out of the map at some stage too.. so not all cars do it..

 

[Ianmc]

My M44 idles consistently at 600rpm.

 

[handsomejackuk]

My M44 idles consistently at 600rpm.

my m44 would idle inconsistently at 600rpm !!!

 

[Jack Ratt]

Missus sez I've been idle all my life

 

[LiftedMuffin]

Once again, thanks for your suggestions everyone! Just to note I do usually fill with 98 octane premium fuel (usually, not always...)

I had a look at the fuel trims just now (pic below) - I'm not sure what 'normal' values would be, but interestingly they didn't budge from 1.5% for "multiplicative mixture adapt" and 10.94% for the throttle valve pot adaptation (not sure if this one is fuel trim related or not). Values were constant whilst the engine was warming up, and when holding at 3k RPM for 30 sec *Headscratch*

The lambda value was hovering very close to 1.001 once the engine had warmed up a bit. One thing I did notice was that the pre-cat o2 sensor voltage was reading 0.0V on the scanner, which if true I would say meant a broken o2 sensor - BUT it was still generating a lambda value??

Anyone got any insights on what this might actually mean in practice?

*Edit - just unplugged the MAF whilst the engine was running and it didn't seem to have much of an affect on the idle. Also read that the o2 senor won't generate a voltage until it reaches operating temperature so could have still been cold when I checked the voltage reading before...

 

[handsomejackuk]

@colb

 

[colb]

I prefer to view fuel trims in live data using my Engine Check Pro software which views in graph form, much easier to see what is going on in that format. I view Short term and long term trims on a split screen when checking them.
A good read with detailed explanation of what you should be seeing is here https://www.bimmerfest.com/forums/showthread.php?t=1158473
As to your exhaust sensor showing nil volts I would certainly get the car up to normal running themp and see what it is doing then. Fault here will affect the fuel trims if its misreporting what it is actualy seeing in the exhaust.
Again live data viuew of the exhaust sensors is useful again in graph format, a working pre cat sensor when up to operating temp should be producing a wave form graph as it ranges up and down the voltages it produces. The post cat sensor when viewed dosn't range up and down the voltage scale and may well look preety static with its voltage.
Not at all sure what your scanner is telling us, dosn't mean much to me but would hazard a guess there is an air leak somewhere.

 

[LiftedMuffin]

Some good info in that thread @colb - thanks! I think the o2 sensor may not have been up to temp before so I guess likely operating in open loop on a default map - will try it after going for a drive and see if I get some better results!

From that thread, it looks like the multiplicative mixture adapt is the short term fuel trim, I'll have to try figure out where the long term one is in my scanner!

 

[t-tony]

Some good info in that thread @colb - thanks! I think the o2 sensor may not have been up to temp before so I guess likely operating in open loop on a default map - will try it after going for a drive and see if I get some better results!

From that thread, it looks like the multiplicative mixture adapt is the short term fuel trim, I'll have to try figure out where the long term one is in my scanner!

This is why an emission test should only be carried out when the engine is up to normal operating temperature.
The co sensor also has a heater element to ensure this happens as soon as possible to get emissions as low as possible as soon as possible.

Tony.

 

[colb]

Not unknown for the heater circuit in these sensors burning out with age so certainly get the car up to temp before believing what you see with fuel trims. Tony is right about the purpose of the heater circuit.

 

[t-tony]

You can check the wires to the O2 sensor with ignition on, one wire must show 12V.

Tony.