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The Audi Doctor
The Audi Doctor, Technician
Category: Car
Satisfied Customers: 2428
Experience:  Over 30 years experience, 17 years with Audi, Factory trained
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I own a 1986 BMW 325es. The car will start on occasion, and

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I own a 1986 BMW 325es. The car will start on occasion, and then stop dead about 15 seconds later. Just like you turned the key off. There have also been times when it would start, and stay running for 15 or 20 minutes. But when it did it would constantly race between say 700 RPMs and 2000 RPMs. For both symptoms when it stopped you could not start the car again right away. Maybe later in the day, or the next day, or the day after that. It is impossible to try to drive the car in this condition. I have replaced the fuel filter, the cold start valve, and the thermo time switch. I replaced both trnsmission mounted speed sensors. I switched out the ignition coil and the fuel pump relay. I removed the fuel pump relay and hot wired the electrical connection to run the fuel pump. The pump runs when hot wired. I've also cleaned the idle control valve. Last week I replaced the distributor cap and rotor. The car is too old to run a fault code check on it. They didn't have that in '86. The value of the car isn't worth spending $1,000 or more trying to fix it. But it is worthless if it won't run. What is my problem?

Thank You for choosing Just Answer for your query. I worked at a large BMW dealership from 1979 to 1989. I was a Tech, shop Foreman, and Service Manager.

When the problem seems complicated the “basics” are often overlooked. It sounds like the electric fan is drawing the system voltage down below “operating threshold“. So I suggest you start with the basics.

Start by checking and cleaning all the connections at the battery. Also check the battery cables and the connections at the ground, starter, and alternator. Also there was a separate ground wire on this year model BMW from the alternator case to the block, so you want to make sure the alternator case is grounded to the engine block. Also check the ground strap from the engine to the frame. Then check the charging system voltage while the vehicle is running voltage should be between 13.8 to 14.2 volts

I suggest you replace both the main relay and the fuel pump relay as they are both problematic for this year model BMW. The main relay is the other relay next to the fuel pump relay on the side of the fuse box. The main relay supplies power to the fuel pump relay as well as the engine computer.

Some other problem areas for this year model are is the ground contact (brown wires) at the back of the intake manifold and the smaller wire(s) that attaches to the positive battery terminal, so be sure and check those as well.

As for the idle speed problem, the correct way to go about diagnosing and correcting this would be to start with the basics. As all of these thing effect the idle and are the foundation for the idle.

Valve lash adjustment correct
cylinder compression within spec.
spark plugs - proper air gap set
secondary ignition wires & resistors within spec. check with ohm meter)
distributor cap & rotor condition
fuel pressure within specification
All boots and hoses free of cracks and leaks

The fuel mixture must be set to specification. I prefer to do this with the crankcase hose at the valve cover disconnected and plugged. With the oxygen sensor still disconnected, reinstall the crankcase hose, the mixture should NOT change. If the mixture goes "lean" there is a crankcase air leak. If the mixture stays the same, pull the dipstick tube, it should go lean.

If you can not get the idle to stabilize to set the mixture, I suggest you make a "Idle valve bypass". I have done so by gutting an old idle valve and then making a few plugs with some small orifices drilled into it. This will give you a consistent volume of air though the idle circuit and stabilize the idle.

Once the mixture has been set hook up the oxygen sensor. The mixture should stabilize at about 0.8% C.O.. Disconnect the sensor and ground the oxygen sensor wire going to the computer, the mixture should go RICH. Reconnect the sensor and it should again stabilize at about 0.8%.

Now you can properly test the idle control system. If the idle is still quite high, try replacing the valve. If that does not do it you will have to replace the Idle Control Unit.

One thing in regards XXXXX XXXXX idle valve and control unit. BMW had a LOT of problems with both of these components. There is a good chance they are failed units. I have even had failed new units. This could be (is) a tough diagnosis. These were troublesome "back in the day", you may need to find an "old hand" at this, that was working on them back in the 80s.

I hope I have answered your questions and addressed your concerns. Should you have further questions on this matter, please do not hesitate to ask. I want you to be 100% satisfied with my answer.

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Thank You!
Jake "The BMW Doctor"
Customer: replied 4 years ago.

There is a fan blade in front of the radiator that I have been told does not work. Might this be the problem, or part of the problem? What do you mean by the fan drawing system voltage down below operating threshold? You have outlined several "connections." If one of those is not clean, or loose, could that be the problem? Is there any chance the computer in the car is bad?

Sorry that was a "cut and paste" error from a previous answer. The electric fan in front of the radiator is not related to your symptoms. The Point I wanted you to get was always starting with checking the "basics". And then THE MAIN RELAY, and then the idle control portion of my answer for the idle speed concern.

Sorry about the error and Thanks!
Customer: replied 4 years ago.

I appreciate the hlep you've given me so far, and these are my last questions. I believe I switched the main rely with the one in my daughter's car some time ago. She has a 1990 BMW 325i. I didn't notice any difference then. If this is a connection problem, then what explains that I cannot start the car right after it stops. And why will it start later in the day, or the next day, if it won't start up again right after it stops? Thank you.

Back in "the day" I changed countless main and fuel pump relays for stall / no start conditions. It was my first "go to" cause. They are cheap, just change them. If you still have the problem after replacing the relays I suggest you check to see if you have spark, and if you have fuel. That would be the next step.

Thank You!
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