I recently bought a 520i auto, and am loving it! Unfortunately, its not running that well, main problem is fuel consumption, I seem to be getting about 15mpg around town just now. Also seems to be running quite rough. I had planned on giving it a service, new plugs, oil and filter change, air filter, to see if this helps. There is also a blow on the exhaust, which cant be helping.
Are there any other simple fixes that could help my fuel consumption? I am a bit paranoid now that it could be a head gasket problem. It isn't overheating, but the coolant looks a bit dirty. Any advice (for a novice!) appreciated.

Hi and welcome. Any air leaks will cause the car to run rough and drink more fuel, have a check of the hoses etc. Your planned servicing won't do any harm either. Maybe think about a coolant change too.

checking the valve clearances might help too.

Thanks for the suggestions. Is there any particular technique when looking for air leaks, or is it just a matter of inspecting hoses for deterioration and such?

Think valve clearances are a bit beyond my limited skills, might have to be a garage job!

You can find big leaks or disconected hoses by a visual inspection, but small leaks are harder to find. Try the old shop method of mixing up some dish soap in a spray bottle, and spraying it around the hose connections and on the hoses themselves, ansy air leaks should show as bubbles, but basically, depending on mileage, I would just replace ALL the vacum hoses and coolant hoses unless the coolant hoses look new and are plyable.

On the tune up, do new plugs, wires, fit a new air filter, change the oil with GTX Castoroil, and set the valve clearence and you should be well chuffed with the result. On the exhaust, hold your hand over the end of the tailpipe and see if you can hear any leaks, if not it may be partially plugged as well. Ask the previous owner when he had the exhuast boxes reaplced if he ever did.

Also test the thermistor sensor in the thermostat the one with the blue plug as it tell the ECU when the engine is warm and to lean of the mixture.

Update on this. I was changing the plugs today and did an inspection of hoses. I found one hose leading into the inlet manifold, big split at the end and held on with sellotape! Hopefully this might have been contributing to poor fuel consumption?

So, stupid question, I have never replaced hoses before, is it just a matter or buying a metre of hose the right thickness and cutting to fit, or is there a specific type of hose required? Where's the best place to go??

Go here: RealOEM

Identify the part then phone your friendly BMW dealer with the part number.

I replaced all the hoses including the rubber boot that sits on top of the engine and it made a big difference. Cost was about £40 for the parts from bmw. Since replacing those parts I have also replaced the spark plugs, leads, dizzie cap, rotor arm and air filter and now getting 22+ mpg around town in my 528 and I have a heavy right foot sometimes.

Sent you a pm listing the stuff I've already investigated. Will let you know of any further developments.

Does this area of the engine look anything like this?

I have been looking through realoem.com to try to find the part number for my leaking hose, unsuccesfully. Can anyone help me identify this part from the pictures below?

That hose that runs over the inlet manifold should be running for asthetic reasons underneathe the manifold.

Where does the labeled pipe go?

Cant help you with what its called but I was interested to see slight differences in the piping arrangements on you car compared to mine (as mentioned in the pm). Anyway here are the same underbonnet shots on my 520i auto. There are quite a few pipes that are the same some of which are routed differently on you car compared to mine, but still do the same job.

However there are others that you have that dont seem to exist in my setup







I guess youre running an earlier setup than mine - what year is your car?

Mine's an 85. There does seem to be a bit of extra pipework on mine compared with your pictures. The pipe I am trying to replace runs over the inlet manifold and then into one part of a three way plastic pipe, part of which connects into beside the throttle body, I think, if that makes any sense at all??

Okay... the latest. As suggested in here decided to strip off the AFM and check it for freedom of movement and cleanliness.

Anyway it wasnt so long ago that I adjust the throttle position switch, and whilst this was being done I cleaned out all the pipework that came apart easily. Today after I'd removed the AFM, I noticed a residue inside the pipe connecting the AFM and thottle body. This residue stinks of petrol. I would've thought that this area should be free of fuel, so what is likely to be causing it. Bear in mind I don't have a cold start injector. Any thoughts?

Heres a pic of the area.



and here is another



As you can see theres quite a lot of it smeared around the pipework

Also whilst I've got the AFM off can anyone give me the a circuit diagram / pinout of whats inside.

I tried putting my meter across the pins to see if I could work out the internal connections but apart from some random varying resistor values, I couldnt figure it out. Update :- just read another thread that says this needs to be done reading a voltage instead of a resistance - it just doesnt work apparently, but still need the pinout.

The pins are marked 5 9 E 7 8. On the wiring loom connector there is nothing connected to E

Sorry I seem to have hijacked your thread robertpat20!

Why dont you pop down your local motor factor and get a length of suitable diameter pipe. Given where it is routed you might get away with not having the specific part as the curvature doesnt look too extreme.

Any update robertpat20? Have you managed to get the hose replaced yet, and if so what difference has it made to the economy if any.

just changed the hose there, bit early to see if it has had any effect as i have only done a few miles so far!

I am thinking that I really need to check the valve clearances checked to improve the running of the car, given the rattle coming from the engine. Is this a realistic task for a novice to carry out, outside? Any special tools required? And are there many possibilities for causing serious trouble if it goes wrong??

Well if you were close, we could go through the pain together as thats the next thing on my list of things to do!! It shouldnt be a difficult job and assuming there are no mechanically duff parts pretty inexpensive as well.