General Information

Complaint:
Popping sound from the engine during startup/engine idles rough during warm-up phase.

Cause:
An unmetered air leak due to an intake manifold backfire during startup may cause a lean condition resulting in a rough idle. Once the oxygen sensor comes on-line, the rough idle condition is eliminated. Field reports have indicated several possible sources for this unmetered air leak.

Action:
If an unmetered air leak is suspected as the cause for a rough idle during the warm-up phase, it is recommended to perform the following quick checks before performing extensive diagnostics.

Check BMW Hardware Number and fault memory of the engine control module.

^ If the BMW Hardware Number is 1 748 837, no EPROM replacement is required. Proceed with normal diagnostic routine.

^ If the BMW Hardware Number is not 1 748 837, the engine control module EPROM must be replaced (see procedure).

Also: Visually check the crankcase vent valve at the rear of the intake manifold to assure there is a vacuum plug on the fitting in the upper left corner.





The vacuum hose for the fuel pressure regulator should be attached to a fitting on the crankcase vent valve (see illustration).

^ If the vacuum plug is present and the vacuum hose for the fuel pressure regulator is attached to its fitting on the crankcase vent valve, the crankcase vent valve does not need to be replaced. Proceed with normal diagnostic routine.

^ If the vacuum plug is missing and/or the vacuum hose is disconnected, the crankcase vent valve and plug must be replaced.





Parts Information:








Warranty Information:
Covered under the terms of the applicable BMW Emissions System Defect Warranty.

Note:
Depending on the level of repair performed, either labor operations 00 51 588 or 00 51 589 may be claimed in conjunction with 00 56 548. Under no circumstances should labor operation 00 51 588 and 00 51 589 both be claimed for this repair.