P1140 code!! Arg... Yes I searched extensively.

[andakn]

You cant run a bmw with the oil cap off. BMWs run the entire engine under vacuum, by pulling the oil cap off you create a huge vacuum leak. If you have a leaky cracked valve cover gasket it can cause a vacuum leak and throw fuel trims off. The only way to be absolutely sure there is no vacuum leaks is to use a smoke machine and smoke the entire intake and engine. It could be as simple as the little vacuum line that runs down to the fuel pressure regulator under the car on the frame rail, or I have also seen a split dipstick tube o-ring.

[FuelCell250]

After 1 year of troubleshooting, I was able to fix the P1140 on my 1997 BMW 318i (M44, auto)! Here's what I tried first:

- Replaced the pre-cat 02 sensor
- Replaced all intake boots and hoses
- Replaced ICV
- Replaced CCV
- Replaced fuel filter
- Checked for pre-cat exhaust leaks
- Replaced DISA valve
- Replaced several intake seals and gaskets
- Took it to 3 mechanics who couldn't figure it out

Eventually, I just sort of gave up and started driving it. A few weeks ago, the car started missing under load or at high speeds. I checked the fuel pressure on the fuel rail (there's a valve you can plug into), and I only had 26 PSI instead of the expected 44 PSI. Weak fuel pump!

I replaced the fuel pump with these parts:

BMW Fuel Pump and Sender Assembly - VDO 16146758736 ($149.99 from FCP Euro)
BMW Fuel Sender Seal - Genuine BMW 16111179637 ($10.99 from FCP Euro)
3/8" or 1/2" hose clamp ($0.99)

The pump is located under the back seat on the passenger's side, and takes less than 30 minutes to replace.

Before replacing the pump, you could see that it was richening itself out as much as possible to compensate:
- Long-term fuel trim: +25
- Short-term fuel trim: -5 to +5

Immediately after replacing the fuel pump, the short-term fuel trim swung wildly in the opposite direction:
- LT: +18
- ST: -15

After about 40 miles of driving, everything completely evened out. The transition was very sudden:
- LT: +5
- ST: -1

For the first 20 miles or so, the car did misfire some more, but it quickly recovered and started running smoothly. In my case, the P1140 perceived lean condition was resolved by replacing a weak fuel pump. There are tons of threads out there just like this one... P1140 with no resolution. I hope this helps someone else with this seemingly incurable problem!