[saadG05]

hi everyone, ( please excuse my non-native English)
I've been experiencing a weird issue with my X5 40i, sometimes when the car is warm it would rough start, sometimes it would take too long to start, or the engine would shake a lot with low RPM, or when letting off the throttle some bangs would come out of the exhaust.
has been almost a year with this issue the dealer is oblivious to what the error is exactly. When reading coolant temps readings in normal conditions 2 years ago it would read around 105C (221F) nowadays its almost always set at 87C (188.8F) which to me feels too low?
when reading fault codes here's what I get:
CD990E: FlexRay, message (request front axle speed,
69.3.4): missing

CD990B: FlexRay, message (request rear axle speed,
69.3.4): missing

1F2505: DME, coding: self-recognition components implausible

118002: Mixture control: Mixture too rich

118402: Mixture control: Mixture too rich, large deviation

(sometimes I get 118001: Mixture control: Mixture too lean)

and recently I've been getting ( catalytic converter efficiency below threshold)
your advice would mean a lot to me!

[eelnoraa]

I am sensing a few different issues.

87C coolant after at steady state is definitely on low side. This maybe link to mixture too rich code. Usually Copland too cold is due to thermostat stuck open. It is a common bmw issue, but usually at higher mileage, say 60-70k

Rough idle and bang when let off gas pedal sound like a miss fire issue. This should generate a miss fire code.

How old is the car?

[saadG05]

the car is stock with 130,000 Km odometer, and no I have never seen a misfire code before, on the last dealer visit they said these faults are caused by the fuel injectors being dirty and they did a fuel injectors cleaning solution.
Can in be faulty injectors?

[eelnoraa]

Oh injector issue csn sure cause the syndromes you described. But bmw should be using index11 or 12 injectors by G05. They should be quite reliable.

Injector can fail in two way.
1. Leaky injector
2. Clogged i injector.

To rule out injector leak, can you remove plug and see if the tip is “wet”? And see if you can smell gasoline? Leak injector can cause rough start up because too much fuel in combustion chamber. But since all injectors cannot gone bad together, the rich code should point to a cylinder, check they plug for wetness. Unfortunately, leaky injector can only be replaced. Those good index injectors are expansive.

Since you have rich code, I doubt injectors are clogged. There is no thing desler can clean injectors without removing them. If injectors are clogged from inside of them, then I would think maybe also should replace fuel filter. Btw, when is the last time fuel filter got replaced?

[saadG05]

I believe the fuel filter has never been change. And I will remove the spark plugs to check for wetness and give an update, but I’d like to know if this fault is not caused from the injectors being (leaky or clogged) what else could give similar symptoms? Can a faulty oxygen sensors cause the same symptoms?

[eelnoraa]

At 130k km, fuel filter is a very nice thing to replace. I recently replaced fuel filter of my older bmw, the filter should have about 70k miles. I can see the fuel coming out from the input port, they are quite dirty. Now now, all gas evaporated, I can share a picture is the left over dirt later.

[bouchy]

My tip is a coolant temperature sensor (or any other...) since you observe problem at a specific temp, also 87°C is quite low (for summer). It might be related to a stuck thermoregulator in open position.
Changing spark plugs and having injectors checked is the simplest.

[saadG05]

Small update, I noticed whenever I start the car in the morning the coolant temps would raise to 90C (194F) then suddenly go down to like 77 C (170F)
Now I believe that the thermostat (heat management system) is faulty