a member a while back posted a downloadable bentley, i belive the first version. if you can find that, it could help people to test any sensor they want to test, and all can be tested including the fuel pump, relays, etc...
a vcg is hard to test, usuall when they go bad, one of or both will happen. oil will leak down the side of the motor, and will burn off the exuasht, the other is it will leak into the cylinders. and if that happens and you get a specific misfire, when you take the plugs out, it should be a dead give away. as matter of fact if you can it, a lot of manuals have pics. of worn out plugs and what should cause them to mess up.
also one part that could play a factor is a air temp sensor, not the one that gives you the outside temp but the one located in the air intake manifold. it monitors the temp of the air in the intake. but that rarely goes bad.
also a disa valve were added after 8/98, so the early e39 don't have them. and folks who have a k&n can over oil them on the reclean, and the extra oil can mess up the maf, so the maf may not be bad.
you also have engine temp sensor, that monitors the temp of the motor, you have two one that goes to the guage and on to the ecu.
and a leaking head gasket can do the trick too. a compression test is the only way to find out.
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