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Misfire and associated problems with my 325i

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Hi guys, I really need some help/advice/a new car! So last April (as in 2020) I bought a 325i on a 57 plate. Body type is e93 (not sure how much of a difference that makes in terms of replies). It developed the rough idle/misfire cold start problem associated with the following error codes:
P0171 - System too lean, bank 1
P0174 - System too lean, bank 2
P2190 - System too rich at idle, bank 2
There is also a 4th code that comes up in reference to a misfire on cylinder 4 but I can't remember the associated code number for that one. Other abnormal things the car is doing and possible symptoms are as follows:
  1. When cold starting, if I gently but steadily press the Throttle, the revs are not steady but instead raise and lower at a uniform speed within a 500rpm range at any speed below 1500rpm.
  2. Sometimes the revs, when idling, drop so low (below 500rpm) that the car sounds as though it is about to
  3. There is a very small oil leak somewhere.
  4. The car has required a top up of around a litre of oil approximately every six weeks.
  5. The chrome tailpipe covers are black with soot.
So here's what I've read as possible causes (if anyone can offer any further causes id be very grateful).
  1. A leak in the vacuum system. Not much more to say on this one other than that I couldn't see any obvious sources but wasn't 100% sure where I should be looking.
  2. A faulty purge valve. I read that "topping up" when filling the tank (pulling the trigger on the pump after auto cut-off stops flow) can force liquid petrol into the valve which is only designed to handle petrol vapour.
  3. Faulty coil pack. Pretty sure this isn't the cause as I've had all packs replaced once and the pack on cylinder 4 replaced a second time.
  4. Faulty spark plug. Again pretty sure that this isn't the cause as these have been replaced twice.
  5. Faulty injector. Not sure how much if any effect it would have on this but I have used fuel from supermarket pumps a few times until I heard it could potentially cause this. Is this true or just the stuff of urban legend? I have since only been using fuel from Shell and BP filling stations. I've also started adding redex to my fuel.
  6. Valves in need of walnut blasting.
  7. Throttle plate in need of cleaning.
These last two are a little bit out of my depth.
The place where I bought my car and have the vast majority of services, mots and repairs done have had a look at it a few times but can't find the cause and aren't bmw specialists so I am taking it to the local dealership for a full bmw diagnosis but this, of course, becomes a very expensive route to go down with them wanting £180 just to do the diagnostic test.
I think that's all of the information I have to offer though one of you may think of something relevant that I have overlooked.
I'd be incredibly grateful for any help or advice any of you might be able to give.
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Welcome to the Forum

The Diagnostic Session at the Dealer will be the most informative 

As for the codes you have all point towards Fuelling issues so I would tend to start there, when was the fuel filter replaced, has the fuel delivery pressure been checked

Check the Vacuum lines very carefully they can fail internally.

Check the looms that feed the Injectors and the Coil Packs for continuity

Buy yourself a BMW capable code reader it will cost less than a Diagnostic session at the dealer. I have an old laptop (Win 8 ) which has BMW 1.4.0 plus INPA/ISTA (both give dealer level information) 1.4.0 was around £10 INPA/ISTA cost £30 when I brought them. I also have programs for Mercedes Volvo and Toyota on the Laptop.

There is a Useful website  www.realoem.com it is a BMW online parts list, put the last 7 digits of your Vin into the search box it will bring up your model then search the relevant section it has useful exploded diagrams that will show where stuff goes. Another USA site is Pelican Parts they have a lot of information with excellent "how to's) complete with pictures the only difference is the steering wheel is on the wrong side.

Good Luck at the Dealer

Let us know how you get on




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 As Greydog recommends, buy the bmw software and plug from the well known selling site. It has proved invaluable for me and saved me a fortune! 
some things to look at. Check the ht leads and the coils to the spark plugs. A failing one will cause a misfire and sporadic Rev drop and a rough idle. 
 You say it has a small oil leak. I would check where this is coming from. Do you have any white smoke or signs of head gasket failure? Any air gaps in the engine will cause all sorts of issues. 
fault idle control valve and air inlet sensor will cause lean running and uneven idle. 
where the air comes in through behind the air filter box is usually a round plug into a square black box with a pipe running through it. Try unplugging that and see what happens. 
thottle position sensor can cause some of the issues above and just needs resetting. 

the software will show all the problems and will point you at the problem. I really suggest you get a copy if you are a competent mechanic. 

good luck and keep us posted. 

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