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Discussion Starter #1
Dear,

My BMW 545i has a strange problem.
1) At cruise control and +/- 1500 rpm , the motor holds in for about 0.5 sec, then ride ok for 30-60 seconds and then again holds in. This repeats during the whole trip.
the strange thing is that this does not happen every day, some days the motor runs smoothly without hickups.
2) when the motor is cold then it never run well for about 2 minutes, when driving backwards, the motor sometimes stops.
3) at idle, the motor runs smoothly most time, sometimes the rpm neadly oscillates from 500 to 1200 rpm though.

My BMW have 74000 miles , LPG is installed at 20000 miles. The problems occurs both at LPG and gasoline.

2 independant specialists already have made a diagnostic, but none of them found the problem.
Computer diagnostics where fine
airmass sensor is already changed, this made the problem even worse, the motor shutted down often. Now i unplugged this sensor , and now it rides much better.
air inlet system is checked with smoke test, this was all fine.

Can you help me?
Thank you
 

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hard to believe no errors are being logged. Even harder to believe car rides better with mass air sensor disconnected.

Car will only do what you mention if no FUEL, no AIR, and worse, timing. You need to get some software and monitor the car as it logs in real time. Other than that, its a crap shoot.
 

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How does it drive when not in cruise control, meaning how does it drive when you do it? Have you ever exchanged your O2 sensors? Have you checked your DISA valves? They can be damaged. That's just of the top of my head..
 

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Start with basics.

Test battery and Alternator. Crazy drive ability issues occur if the numbers are all wrong.
Given that it occurs on gas and lpg, you've ruled out gas fuel pump issue. But I don't know how those two systems switch over.
Check all the vacuum lines under the bonnet. Leaked can mess things up.
 

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Discussion Starter #5
It drives well when not driving at cruisecontrol. but my feet acts not so well behaved as my cruise control :)
O2 is not replaced yet, Disa valves not checked , i will check in few days and let you know. Thanks
 
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