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Join Date: Jan 2016
Location: Dresden, Germany
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Rough idle, worse with A/C off
My '99 M5 is idling rough at the moment and I noticed that it's a lot smoother if I switch the air conditioning on.
Any idea why that might be?
I'm thinking that the change of load on the engine could just be damping out the roughness or possibly the engine is just operating at a slightly different point in order to drive the A/C.
Could this shed some light on the cause of the roughness?
A little background: I also noticed that B1 and B2 LTFT are ~10% and 17% respectively as reported by Torque Pro, INPA is currently showing 1.11 and 1.18 'Adaptation value multiplicative'. These come down quite a bit after extended cruise on the autobahn. INPA is showing that the B2 cam timing is ~2degrees more advanced at idle than B1 which was also a surprise because I though VANOS should adjust them and then they should be equal?
I've checked for vacuum leaks and checked the O2 bungs for cracks.
Spark plugs, coils, MAF, Cam and Crank sensors, fuel pump, and VANOS solenoid valves are all relatively new. The car passed both the MAF and VANOS tests.
Any ideas appreciated, I will drop it down to the werkstatt soon if I don't figure it out.