I have an '84 318i coupe E30 that runs very well. However, on rare
occassion the rpm's will drop to 1000-1100rpms and hover. When one
attempts to press gas pedal, the car doesn't die but rather acts like
it's only running on 2 cylnders. Sputter-sputter-sputter......, then
miraculously is seems to recover and runs fine again for a week or
two. Every shop I've looked into advice, tells me to either sell it
or it'll cost over $1000, but doesn't fix the problem. Air mass
sensors, fuel pressue regulators, even thermostat, as if.
One I know of was a faulty/sticking AFM. Junkyard has 'em cheap if you pull
it. Ebay often costs more. It can stick or bind at the closed (idle) end.
You can tell by removing the air filter side and sticking your finger or a
screwdriver on the flap and pushing. You'll feel the bind as a scraping. It
may be dirt buildup or metal twisting enough to catch along the path. Fuel
filter would be a good idea, too (as John Burns recommended). If it's
running otherwise, the relay my be OK, but a spare wouldn't hurt. You can
get another at the same yard as the AFM, usually for free.
I like how "fixers" try to go way too far...sell it (to me!) or pay $1000
(pushing to sell to me!). What a joke. They'll fix it for $10 and keep it or
sell it for $$$ and add "BMW mechanic-owned" to pump up a supposed trust
from the buyer. "OOHH! A BMW mechanic!" I just wet my pants!
Bill in Omaha
You are describing the affect of an engine being fed more air without the
added benefit of more gas.
I'd consider stuff like fuel filter, fuel pump, throttle position sensor. Of
the three, it occurs to me that the first two are relatively static -- once
they misbehave, they're likely to not recover by theirself -- but the
throttle position sensor is an electronic device that is, by its nature,
capable of intermittent failures.
Of the three, the filter is the cheapest to replace, and even if the problem
is not resolved, there is a good chance you need one.
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