BMW E46 323ci - Unmetered air leak - Help

[vinzchau9]

Hi all,

For the last 10 days I believe I have been experiencing an unmetered air leak on my BMW E46 323ci.

When I start the car from cold I am experiencing idle hesitation and the engine feels like it's shaking. When I drive off and take my foot off the gas, the car starts to judder. What is strange is that after 10 minutes of driving or when the car is at operating temperature, if I switch the car off and on again the issues go away and everything is as it should begin. Even if I drive for say 30 minutes or so without switching the car off, the issues will go away.

So far I have checked all the intake boots to the icv and throttle body and they all in good condition. I have cleaned the icv and checked the DISA valve for correct operation and everything is as it should be. I have also done some diagnostic live data checks and have noticed the STFT in Banks 1 and 2 are around +20%, which from what I have read indicates it's above acceptable tolerance and would indicate a vacuum leak. Even the MAF g/s looks low at 2.9g/s when at idle once fully warmed.


This evening I had a host of P codes come back ranging P0170 and P0173 (fuel trim codes) to P0302 to P0306 (cylinder misfire detected codes). The engine light came on but went off when I checked for fault codes.


Can anyone advise what it could be or if anyone has experienced the above issues. I am really at a wits end with this. Thanks

[MarcoZandrini]

You don’t have the classic indications of vacuum leaks: codes P0171 and P0174. What tool
are you ysivgbyo scan the engine computer? Is the fuel pump original? When was the fuel filter last changed? Since your car is a 1999 model, it has a separate fuel pressure regulator. I’m betting the pump is soft failing. This means the pump can’t consistently pump enough gas at the required 50psi. Luckily your engine, an M52, does have a fuel pressure test port on the fuel rail. Item #2 in the link is the cap to the port: http://www.realoem.com/bmw/enUS/show...diagId=13_0644. Pressure has to be 60psi or greater at all engine speeds under all engine loads.

Start there. If the pump is the culprit replace it with a Siemens/VDO pump only. Replace the filter at the same time. Filter brands are Mahle and Keyser.

[RobertDenali]

Use a smoke machine to find the source of vacuum leaks. I just performed a major service on mine to include removing the DISA, air intake manifold and replacing the Oil separator CCV system. After performing this work I had a slightly rough engine issue at idle that was more noticeable when cold.

I did not have P 0171 or 174 codes.

I found by using a smoke machine the issue to be the DISA gasket was leaking air and one of the new CCV hoses was leaking as well.

After resolving these two issues the engine is again smooth at idle.