Hi everyone. Having a running issue with the z. When it's cold it runs roughly idling at around 600 rpm and feels as though it's going to cut out but rarely does. There is also a kind of wobbly sound in the tone of the exhaust. When it warms up it's like a different car. It feels like there is more power and the exhaust reverts back to a very smooth sound. It has started flipping between these 2 scenarios even when hot. I'm a bit new to all of this so any suggestions would be greatly welcomed.
Running rough with intermittent limited power
- Thread starter Gilles
- Start date
Which engine do you have in your car? The 4 cylinder M44 or a 6 cylinder?
Do you have access to a scanner? If so scan the car for trouble codes. Also let us know what the fuel trims are with a hot engine at idle. A 4 cylinder car will have a short term and a long term fuel trim. a 6 Cylinder car will have 2 short term and 2 long term fuel trims.
Many rough idle problems that change between cold and hot running are caused by vacuum leaks. Have a good look at the rubber boots between the Mass air low meter (MAF) and the inlet manifold for cracks or leaks.
Do you have access to a scanner? If so scan the car for trouble codes. Also let us know what the fuel trims are with a hot engine at idle. A 4 cylinder car will have a short term and a long term fuel trim. a 6 Cylinder car will have 2 short term and 2 long term fuel trims.
Many rough idle problems that change between cold and hot running are caused by vacuum leaks. Have a good look at the rubber boots between the Mass air low meter (MAF) and the inlet manifold for cracks or leaks.
When the car first starts, The engine computer (DME) runs in open loop mode. It uses in built fueling tables for the mixture. The O2 sensors are not used. When the engine heats up, it goes to closed loop mode, uses the O2 sensors to see what the level of oxygen is in the exhaust and trims the fuel to get the correct mixture.
A vacuum leak can cause rough idle when cold because there is unmetered air getting into the inlet and this upsets the mixture as open loop mode can't adjust for the extra air. When you get to closed loop mode the engine Computer (DME) uses the O2 sensors and can compensate for the extra unmetered air. If the vacuum leak gets really bad, the O2 sensors and DME can not compensate enough and the rough idle occurs on the hot engine.
A vacuum leak can cause rough idle when cold because there is unmetered air getting into the inlet and this upsets the mixture as open loop mode can't adjust for the extra air. When you get to closed loop mode the engine Computer (DME) uses the O2 sensors and can compensate for the extra unmetered air. If the vacuum leak gets really bad, the O2 sensors and DME can not compensate enough and the rough idle occurs on the hot engine.
Thanks a lot for the explanation @Murray Wall. Any suggestions on an obd2 reader?
There are many options for a OBD2 reader.
For just the engine, a cheap and very good option is the smart phone app OBD Fusion and an appropriate OBD2 Wifi (OSi) or Bluetooth (android) adapter. See link on setting up OBD Fusion for diagnostics and logging. https://www.e46fanatics.com/threads/obd-fusion.1240733/
Look at the Foxwell NT530 scanner with BMW software. https://www.foxwelltool.com/wholesale/nt520-pro-scanner-with-bmw-software-installed.html
For just the engine, a cheap and very good option is the smart phone app OBD Fusion and an appropriate OBD2 Wifi (OSi) or Bluetooth (android) adapter. See link on setting up OBD Fusion for diagnostics and logging. https://www.e46fanatics.com/threads/obd-fusion.1240733/
Look at the Foxwell NT530 scanner with BMW software. https://www.foxwelltool.com/wholesale/nt520-pro-scanner-with-bmw-software-installed.html
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I had an intermittent fault with rough running on my wife's 2.0. May not be the same but it's a cheap fix and my indy didn't find it after £400.
When you have the issue, undo the fuel cap to see if you get a rush of air.
If so there is a solinoid that saves the Z3's farts into a charcoal canister (petrol vapor). This failed on mine intermittently and so gave intermittent rough running.
2nd hand genuine OEM one off ebay, and a common part across many BMW's at least; ~£10
When you have the issue, undo the fuel cap to see if you get a rush of air.
If so there is a solinoid that saves the Z3's farts into a charcoal canister (petrol vapor). This failed on mine intermittently and so gave intermittent rough running.
2nd hand genuine OEM one off ebay, and a common part across many BMW's at least; ~£10
Plugs/coil packs?
Then warm it up nicely then take it for a long Italian tune I'd say.