Re: 318i engine run problem ('84) (archive)

Just went through a whole bunch of stuff trying to get to the bottom of idle problems with my 85 -318i. There are a lot of things you can and will want to check, but you may have to go to a dealer, or someone who specializes in Bosch fuel injection (think someone who works on VWs or Saabs can help).
If you are going to to try to work this through yourself, i highly recommend getting a Robert Bently "3-Series Service Manual" (if its not available from Borders, or Barnes and Nobel, Mr. Bentley has a web site where you can get it). Has sections on how to test all the components that feed into the injection/ignition system (see sections on Driveability, Fuel System and Ignition). Mr. Bentley also has "How to Understand, Service and Modify Bosch Fuel Injection & Engine Management". Its also a help on the trouble shooting, but the "3-Series Manual" should get you through.
Before i got the problem straightened out, i replace the fuel pressure regulator, Fuel pump relay, temperature control switch, and finally the idle control relay (that part is expensive, around $200). All those things tested bad or were somewhat questionable.
When i started into this, a lot of the underhood connectors were really corroded. I started with cleaning everything with either electrical cleaner, or emmory boards, pencil erasers, or just flat out cut off and replaced the offening connectors. Previous owner didnt take care of the obvious stuff.
Assuming the connectors are all ok, i think i would start with the air bypass (aka: idle air stabalizer) valve, becaue it sounds like you have spark, since it starts and also fuel, for the same reason. The air bypass valve is often a problem and if not opening and closing right will kill the idle.
The valve is attached to the plumbing on the top of the engine (passenger side) next to the throttle/air intake manifold assembly, near the end of the fuel rail. I pulled mine off and found it to be all gunked up inside with carbon and greasy sludge. I hosed it down with liberal amounts of carb cleaner until it was spotless. i cheked to make sure it opened and closed by attaching a 12vdc power source. The normal valve resistance is suppose to be 9 to 10 ohms as measured with an ohm meter. If the resistance is significantly higher, the valve is shot.
When i re-installed it, i put an ammeter in the circuit and made sure i adjusted the current draw to the proper spec. Also, the two pronged connector was fairly loose. i crimped the metal female connectors down a little and tie wrapped the connector body so it was snug. You will have to check the Bentley Manual for the right current draw, and adjusting screw location, i think its different depending on when the car was built. I have a newer version.
Another place to look is the fuel pump realay, another common problem. It is on the driver side mounted on the side of the strut housing. There is a black plastic cover that pulls off to reveal three relays. The smallest square black one is the fuel pump relay (mine was the relay toward the front of the car). As they wear out, the points get pitted and you may get enough current to get the fuel pump going, but it can drop out if the relay points are bad, as the relay continues to heat up with more and more current draw.
The ideal thing would be if you have access to another 84/85 318i that you can swap components with, so you dont have to keep replacing things till you get to the bottom of it. Electrical stuff for these cars is often out of stock and cant be returned.
Im still having some minor idle problems, but after a lot of trouble shooting and replacing some important things, as per above, the car is running well.
Hope it works out for you.
Wolfgang ;)

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