BMW Repair: BMW 528i Fuel Consumption, vacuum hoses, airflow meter

Question
Hi Tino,

Since I had starte the investigation thought I would complete the same. Earlier you had suggested some areas of improvement if I wanted to bring the performance of my 1996 BMW 528i upto factory specs. Out of all areas you had pointed out, I research on the net & all are relevant however some are relatively cheap & easy to fix & others not so. I should definately be able to correct the ones that are cheap & not difficult. Can you pl. help with the foll. as per your suggestions:

- Improve compressions - I had it checked & it measures up to where it should be, does it mean it is fine or is there anything else to be looked at?

- Valve should be reset - what does this involve?

- all vacuum hoses should be replaced - Cracked hoses I believe are often a cause for poor mileage. Hoses aren't expensive, can you pl. advise a way to inspect whether hoses need replacement & the best way of going about it?

- Replace all injectors/ spark plugs - Have replaced all spark plugs, what is the way to find out if injectors need replacement? Got carbon cleaning done recently, is this enough? How could one determine whether injectors are in good condition or not?

- reseal intake manifold - How to find out if it needs resealing & the best way to reseal it if needed?

- Replace air idle valve, o2 sensors & airflow meter - How can i find out whether these things need replacement & the best way to do it if needed. something such as the O2 sensor isnt too expensive.

Thanks,

Janak.

Answer
Dear Janak,
If your compression values are OK, then the valves are also OK.
The vacuum hoses are fairly easy to identify and replace.
Ask your mechanic to test all the vacuum hoses for leaks
and replace the bad ones. Also test the front intake air boots , the seals of the throttle valve, and the end cover valve (crankcase vent valve) at the rear end of the engine.
I dare not recommend that you do the testing with a brake cleaner spray since it is potentially dangerous being a fire hazard. Replacing the throttle valve seal/0-ring is pretty easy. But replacing the end cover valve or re-sealing the whole intake manifold is not for a do-it- yourselfer.
As to the idle air valve,02 sensors and airflow meter, you need a sophisticated OBD2 scanner (not the mickey mouse
ones that do not show active datastreams) to be able to find out if they are working properly or not. I do not recommend replacing anything without confirmation that they are really bad.
I would suggest that for you to save time and money, bring your vehicle to a dealer and have it diagnosed for the last three items.
Tino