Need your help. Rough Idle

[bbs47]

Hello all the way from the country of Georgia!

I own a 2012 F10 M5 with over 138k KM (85k Miles), did a full engine rebuild a month ago changing all of the gaskets and plastic parts. I also went for forged H beam connecting rods.

Everything is running great and I am really satisfied that the car has been brought back to life, but I encountered a very irritating issue. rough idle... the RPM swings back and forth by 50-150 RPM... No error codes, no check engine lights. I changed the crank ventilation valves and fuel tank ventilation valves that sit on top of the engine, as recommended by people who had the same issue, unfortunately it did not solve anything.

Can you please suggest what should I do? Here are the list of options that I can check/do tomorrow:

1. throttle body deterioration
2. idle adaptation via ISTA
3. faulty o2 sensor
4. HPFP check values with ISTA (but i doubt it because somebody said that it causes rough idle and bad performance but the car is at its performance peak.)
5. cleaning the MAF sensors.

Anything else that I should check?

Looking forward for your replies

[M5_Raz]

Originally Posted by bbs47

Hello all the way from the country of Georgia!

I own a 2012 F10 M5 with over 138k KM (85k Miles), did a full engine rebuild a month ago changing all of the gaskets and plastic parts. I also went for forged H beam connecting rods.

Everything is running great and I am really satisfied that the car has been brought back to life, but I encountered a very irritating issue. rough idle... the RPM swings back and forth by 50-150 RPM... No error codes, no check engine lights. I changed the crank ventilation valves and fuel tank ventilation valves that sit on top of the engine, as recommended by people who had the same issue, unfortunately it did not solve anything.

Can you please suggest what should I do? Here are the list of options that I can check/do tomorrow:

1. throttle body deterioration
2. idle adaptation via ISTA
3. faulty o2 sensor
4. HPFP check values with ISTA (but i doubt it because somebody said that it causes rough idle and bad performance but the car is at its performance peak.)
5. cleaning the MAF sensors.

Anything else that I should check?

Looking forward for your replies

It can also be a vacuum line not being connected/leaking air. Good luck, hope you find it soon

[Blaxwil]

Using your list of options to start tomorrow, start at the bottom. "Cleaning the MAF sensors". It's not only the cheapest option on your list but it's also very likely to be the issue. Just remember to use a MAF sensor cleaner only.

[bbs47]

Originally Posted by Blaxwil

Using your list of options to start tomorrow, start at the bottom. "Cleaning the MAF sensors". It's not only the cheapest option on your list but it's also very likely to be the issue. Just remember to use a MAF sensor cleaner only.

welp.. i cleaned the maf sensors, nothing changed. Somebody noted out the MAP sensors on the intake manifold, will check that as well... My AC compressor needs changing btw, its on its brink of existance, can that be the cause of the rough idle?

[bbs47]

Originally Posted by M5_Raz

It can also be a vacuum line not being connected/leaking air. Good luck, hope you find it soon

Vacuums are good, checked everything either its a sensor or cylinder head, hoping its some kind of sensor

[Blaxwil]

welp.. i cleaned the maf sensors, nothing changed. Somebody noted out the MAP sensors on the intake manifold, will check that as well... My AC compressor needs changing btw, its on its brink of existance, can that be the cause of the rough idle? [/QUOTE]

The sensors located on the sides of the intake manifold are the ones I was referring to. Sorry for not being very clear but I didn't know there was another set of sensors.

[bbs47]

Originally Posted by Blaxwil

welp.. i cleaned the maf sensors, nothing changed. Somebody noted out the MAP sensors on the intake manifold, will check that as well... My AC compressor needs changing btw, its on its brink of existance, can that be the cause of the rough idle?

The sensors located on the sides of the intake manifold are the ones I was referring to. Sorry for not being very clear but I didn't know there was another set of sensors.[/QUOTE]

No worries, wanted to clean the MAF sensors on the cold air intake they were pretty oily due to faulty PCV. Today I got the P0175 code, not sure what tf is wrong with this car, most likely I am going to leave it to a mechanic and tell him to fix whatever is wrong, don't have the nerves to pursue more DIY troubleshoots...

[technician117]

Originally Posted by bbs47

The sensors located on the sides of the intake manifold are the ones I was referring to. Sorry for not being very clear but I didn't know there was another set of sensors.

No worries, wanted to clean the MAF sensors on the cold air intake they were pretty oily due to faulty PCV. Today I got the P0175 code, not sure what tf is wrong with this car, most likely I am going to leave it to a mechanic and tell him to fix whatever is wrong, don't have the nerves to pursue more DIY troubleshoots...[/QUOTE]

If the MAF's were actually oily looking, a MAF cleaner will usually not be a good fix. You might want to replace them. How many miles on primary O2 sensors? Those are cheap and easy to change and do affect how the engine will run.

P0175 I think is a lean code. MAF's, primary O2's, and vacuum leaks can cause the code (among other reasons). Are you certain the vac line to the mufflers is connected or plugged off?

[bbs47]

Originally Posted by technician117

No worries, wanted to clean the MAF sensors on the cold air intake they were pretty oily due to faulty PCV. Today I got the P0175 code, not sure what tf is wrong with this car, most likely I am going to leave it to a mechanic and tell him to fix whatever is wrong, don't have the nerves to pursue more DIY troubleshoots...

If the MAF's were actually oily looking, a MAF cleaner will usually not be a good fix. You might want to replace them. How many miles on primary O2 sensors? Those are cheap and easy to change and do affect how the engine will run.

P0175 I think is a lean code. MAF's, primary O2's, and vacuum leaks can cause the code (among other reasons). Are you certain the vac line to the mufflers is connected or plugged off?[/QUOTE]

I have investigated and found a leak coming from the fuel tank ventilation which is located underneath the rear right wheel arch. No other leaks from anywhere. MAF's have normal readings. Might also change the MAP sensor on the left bank's intake manifold. Will change that ventilation system today and see if that gives me any results, hopefully it does

[WH1TE_M5]

Did you fix this issue ?