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BMW E30 318i – Will Not Idle, L-Jetronic, Vacuum Leak, M10

July 6, 2011

Q
I have purchased from you items in the past. i still own and keep in immaculate condition a 1984 bmw 318i, among my other older model vehicles. My engine is in top shape, garaged, battery connected to a 3 stage electronic charger, started and idled periodically, but lately it is not able to ignite the air/fuel in the system.
i have checked there is no fuel delivery problem from the fuel pumps as they are working properly. if i am able to start the engine, i rev at 2000 rpm, but when left to idle, it will idle for less than a minute, sputter, and terminate. other than being garaged and started and idled periodically, there has no significant change in the use of the vehicle. i have the Bentley service manual, but any of these – fuel pressure regulator, fuel injection system, oxygen sensor, idle air stabilizer, or air flow sensor – can be the culprit and i need a more definitive device to help me diagnose the cause. is there such a device?
is there an engine analyzer that i can buy like an OBD-1 or OBD-II that can analyze engine condition of this engine? I have an actron OBD-II autoscanner for my vehicles (for later than 1996). or, is there an adapter to the OBD-II and software that can be adapted to this OBD-II autoscanner that can diagnose engine problems for this engine?

A
The 84-85 318i models have the Bosch L-Jetronic fuel injection system. These models have a separate ignition system (Bosch electronic) and the L-Jetronic fuel system. There are no internal diagnostic capabilities with these engine management systems.

We will assume that you do indeed have spark, and that this is not the root cause of the symptoms that you mentioned, since the engine does start and run if you keep it above idle. This leaves us with fuel control and the intake system.

Your symptoms do suggest a large vacuum leak in the intake system and this should be your starting point for diagnosis. Typically, this would be a cracked rubber intake boot, bellow or air hose. Inspect every rubber hose, boot and fitting that carries air. This includes the crankcase ventilation, intake and idle control circuits.

Can you keep it at an idle speed by using the throttle (vs. just letting it sit at the idle position), or will it not run at a properly low idle speed at all? Let us know what you find.

We do keep all of the intake boots, bellows and hoses in-stock (click below).

BMW

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