Rough Idle - BMW 2.5 SI

G

greggy50

Member
Hi,

My Z4 has developed a rough idle the last couple of weeks (2.5 SI) but is showing no warning lights on the dash.

Yesterday it sounded like it was running on partial cylinders and was tapping badly suddenly re-starting after I had parked up whilst it was hot and then it seemed to clear and go back to normal again after a couple of minutes as it had me worried something was majorly wrong. An engine light did appear at this point and then disappear once it cleared up.

I replaced the Vanos solenoids about a month ago with after-market ones but doubt it would be that? I have also just cleaned the MAF sensor but it didn't seem to help.

My thoughts are its probably the plugs or coil packs? I have ordered some new plugs to install which I will do tomorrow (the existing ones are only 2 years and 30k miles old) but I am unsure how to check the coils without a reader?

The car also seems a bit flat to me below 4k even after changing the vanos solenoids however I suspect this is more my daily driver is a 400bhp electric car and the car itself is fine.

Thanks,
Greg
 
A bad Maf will make the car feel flat, seems to be held back when driving it, had that with mine, new Maf cured it instantly. Oem part dont try cheap ebay units, stick to Bosch or Siemans brands that were oem fitments. Bad Maf won't set EML on its own, when you do get an EML its usually set by sensors further down the the system being affected by a faulty Maf.
 
Have you checked the condition of your DISA valve? If the pin at the end is coming loose this can mean the flap isn't correctly positioning for idle and also not opening properly for higher rpm
 
Disconnect your MAF and see if the engine runs better. If it does run better your MAF is bad.
 
Had a similar issue that I managed to resolve OP.

I had a rough idle, especially on start up. Also, when I would drive (I have a manual), I would get hesitation between 2,000-4000RPMs, almost like it was running on less cylinders. It would stutter, hesitate and it began to get more severe as time went on. It almost felt similar to losing traction. I thought it was the fuel pump, ABS, MAF sensor etc etc. I started to get worried that it was my engine on the verge of failing. I have 162,000 miles on it.

Turns out, I hadn't replaced my sparkplugs in years so it was time for that. I also replaced a coilpack that I suspected was bad (because I had replaced it once before and the newer coilpack looked a lot different). IT MADE A HUUUUUUUUGE difference. It's like night and day now--all of the problems I had with the car are completely gone with new spark plugs and diagnosing the bad coilpack. Car pulls much stronger now, perfect idling and no hesitation at any RPMs in all gears. It feels like a whole new car. :)

Just a tip: I ordered a coilpack directly from BMW and it looked different than the other OEM coil packs in my engine... My replacement was a full rubber coilpack that looks smilar to what would work for your generation Z4. My OEM coilpacks had a plastic jacket sleeve that looked a lot different. I'm telling you this because I would suggest finding out the exact coilpacks your car uses and take one out and make sure it looks virtually identical. Because on my 2003 Z4, it seemed to cause some issues.

Good luck!
 
BumpyZ4 said:
Disconnect your MAF and see if the engine runs better. If it does run better your MAF is bad.
Click to expand...

I have tried that, it didn't seem to make a difference apart from the revs increased as I switched the car off without it plugged in.

I will try and do a video if the plug change doesn't do the trick but do think it may be a coil.
 
Aaronb76 said:
Have you checked the condition of your DISA valve? If the pin at the end is coming loose this can mean the flap isn't correctly positioning for idle and also not opening properly for higher rpm
Click to expand...

Is the DISA a problem on the N52 engine? I thought it was just the earlier ones.
 
Motionblurrr said:
Had a similar issue that I managed to resolve OP.

I had a rough idle, especially on start up. Also, when I would drive (I have a manual), I would get hesitation between 2,000-4000RPMs, almost like it was running on less cylinders. It would stutter, hesitate and it began to get more severe as time went on. It almost felt similar to losing traction. I thought it was the fuel pump, ABS, MAF sensor etc etc. I started to get worried that it was my engine on the verge of failing. I have 162,000 miles on it.

Turns out, I hadn't replaced my sparkplugs in years so it was time for that. I also replaced a coilpack that I suspected was bad (because I had replaced it once before and the newer coilpack looked a lot different). IT MADE A HUUUUUUUUGE difference. It's like night and day now--all of the problems I had with the car are completely gone with new spark plugs and diagnosing the bad coilpack. Car pulls much stronger now, perfect idling and no hesitation at any RPMs in all gears. It feels like a whole new car. :)

Just a tip: I ordered a coilpack directly from BMW and it looked different than the other OEM coil packs in my engine... My replacement was a full rubber coilpack that looks smilar to what would work for your generation Z4. My OEM coilpacks had a plastic jacket sleeve that looked a lot different. I'm telling you this because I would suggest finding out the exact coilpacks your car uses and take one out and make sure it looks virtually identical. Because on my 2003 Z4, it seemed to cause some issues.

Good luck!
Click to expand...

I will be changing the plugs over the weekend so will see what that does but I do think it will be a dodgy coil myself.

Any idea how I can check? Is it a case of buying one and swapping each one until the idle sorts itself out...
 
Check to see if it’s throwing any codes with a code reader. If it is, swap the suspected malfunctioning coil with one next to it. Clear the codes. Then drive again and see if the misfire code moves to the new spot. If it does, bringo you found your coil.
 
greggy50 said:
Aaronb76 said:
Have you checked the condition of your DISA valve? If the pin at the end is coming loose this can mean the flap isn't correctly positioning for idle and also not opening properly for higher rpm
Click to expand...

Is the DISA a problem on the N52 engine? I thought it was just the earlier ones.
Click to expand...

No you're right just the M54, I missed the SI bit skim reading!
 
Camshaft position sensor cured my rough idle. Not cheap, but if you have ruled out the ignition system, then worth considering.
 
Well, I have changed the plugs today and it seems to have solved it as the car was running a lot sweeter.

I'll take it for a test drive shortly.

The plugs were only 2.5 years old so it surprises me it has made such a difference...
 
greggy50 said:
Well, I have changed the plugs today and it seems to have solved it as the car was running a lot sweeter.

I'll take it for a test drive shortly.

The plugs were only 2.5 years old so it surprises me it has made such a difference...
Click to expand...
So were they just worn? No signs that fuel or oil may have been leaking onto them?
 
enuff_zed said:
greggy50 said:
Well, I have changed the plugs today and it seems to have solved it as the car was running a lot sweeter.

I'll take it for a test drive shortly.

The plugs were only 2.5 years old so it surprises me it has made such a difference...
Click to expand...
So were they just worn? No signs that fuel or oil may have been leaking onto them?
Click to expand...

Not really, they had carbon build up for sure but they didn't look horrendous for coming out of a engir with 120k miles on. I have noted in 2018 the car was on 84k and its 122k now so they have seen a fair bit of mileage.

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greggy50 said:
Not really, they had carbon build up for sure but they didn't look horrendous for coming out of a engir with 120k miles on. I have noted in 2018 the car was on 84k and its 122k now so they have seen a fair bit of mileage.
Click to expand...
Ok, so that hopefully shows there isn't another issue, just tired plugs?
 
enuff_zed said:
greggy50 said:
Not really, they had carbon build up for sure but they didn't look horrendous for coming out of a engir with 120k miles on. I have noted in 2018 the car was on 84k and its 122k now so they have seen a fair bit of mileage.
Click to expand...
Ok, so that hopefully shows there isn't another issue, just tired plugs?
Click to expand...

Hopefully so, just don't about 20 miles in the car and it does seem to be running better to me.

It doesn't seen massively punchy low down but I think my Polestar 2 has ruined my perspective. I was in a new 35 TDI A4 the other week and I thought it was broken it seemed that slow...

I think overall its a sign that I need to upgrade to a Z4M Roadster :rofl:
 
You dont say why you replaced the VANOS Solenoids? Did you have a confirmed fault from a code reader?
Your plugs dont look bad to me - lean running but thats modern engines for you.
Sure you dont have any air leaks?
Start at the Oil filler cap and have a good look and listen all around the induction system.
Otherwise suggest you review fault codes and proceed from there, I have found that is the first stop with any diagnosis.
Shotgun diagnosis is usually a waste of time and money.

My Chinese VANOS solenoids fixed my problem ( Identified through Fault code diagnosis) and are still running strong after 2 years and 15K miles.
 
Rucky said:
You dont say why you replaced the VANOS Solenoids? Did you have a confirmed fault from a code reader?
Your plugs dont look bad to me - lean running but thats modern engines for you.
Sure you dont have any air leaks?
Start at the Oil filler cap and have a good look and listen all around the induction system.
Otherwise suggest you review fault codes and proceed from there, I have found that is the first stop with any diagnosis.
Shotgun diagnosis is usually a waste of time and money.

My Chinese VANOS solenoids fixed my problem ( Identified through Fault code diagnosis) and are still running strong after 2 years and 15K miles.
Click to expand...

Hi,

I did the solenoids as it felt really flat low down and it did seem to help a bit to me.

The car seems fine now I have changed the plugs today but will see how it goes.

I don't have a code reader unfortunately... they are no warning lights on the dash however.
 
Glad its fixed,
- the code reader also allows viewing of live data and stores codes that might not have triggered a fault light - yet
I can get live engine, transmission, steering and braking data with my icarsoft so its pretty useful to have one
 
Rucky said:
Glad its fixed,
- the code reader also allows viewing of live data and stores codes that might not have triggered a fault light - yet
I can get live engine, transmission, steering and braking data with my icarsoft so its pretty useful to have one
Click to expand...

How much are they? I may invest in one if you can use it on multiple cars.
 
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