Idle Issue's

[J!m]

Generally all BMWs suffer from poor idle from leaks in the intake somewhere.

In general, check all vacuum hoses and intake boots and hoses, with particular care taken with any and all hoses/boots AFTER the air mass meter. Leaks before CAN cause problems but after the air mass meter is critical (someone recently had trouble due to an improperly attached air filter lid that allowed the ingress of hot under hood air under certain conditions and this sudden air temp- and therefore density- change caused some problems).

A small leak here can cause big problems as the car does not have accurate air mass numbers and then the exhaust lambda sensors see a too lean condition and it starts adding fuel (usually too much initially). In between that cycle of incorrect intake mass and exhaust dilution and over-fueling, it runs like crap. As it warms up (actually learns where the fuel needs to be with the leaks it has) it will run better, looking like a temperature related issue, where it is actually a time related issue.

Simple problems can be difficult to determine sometimes, so always check for leaks first, then look elsewhere.

[Woksgolfy]

Hi J!m thanks for your feedback that's great advise I will save that to my records for future reference

Cheers Woks.

[Gigantor33]

My 98 318ti began to idle rough and it was hard to start after sitting overnight , this was shortly (maybe a week or so) after I had replaced vacuum hoses and replaced cooling connectors behind the motor and under the intake manifold. I had first thought it was related to the work I had just done. I was frustrated at first, because I was really careful on replacing the vacuum lines and hoses.
I did notice a hissing sound from the (CCV) Crank case vent valve. which didn't sound normal to me. Replaced the CCV and it ran great and started with no problems.