I recently acquired a 1990 325i with 191000 miles on it. It is in very good shape and has been cared for very well. It seems to run very good and looks very good. I have two questions
It's not hard. But if you don't know then I'd suggest you purchase a service manual such as Bentley's.
Which light exactly?
There should be 4 spring clips that join the top and bottom of the air box together. Pry those apart with a screwdriver and remove the air filter. Go to this link, see part #3. That's the clip.
You need to find out the code. On OBDI cars like your's, follow the instructions here...
Sounds great, enjoy your car. Be sure to keep the timing belt changed at the prescribed intervals. That is one failure that would put a damper on your fun for a while.
The Check Engine light after a long decent is probably a sign that the engine is running slightly lean at idle, as measured by the Oxygen sensor (assuming here that you have one). This is accentuated by the engine running at higher rpms as occurs with engine braking. If you extract the check engine diagnostic codes this should come back with something like "engine mixture too rich/lean". As I recall, older models were not able to report which condition was occuring, just that there was a fault with that particular parameter.
I don't think it is a big problem if that is all that you have, but keep an eye on things and see if it gets worse and happens at other times.
-Fred W
On my 89 325is, I always had a problem with the check engine light coming on while engine braking on a long downhill. My foot was off the accelerator, the RPMs maybe in the 3000 range. It's running leaner and would trigger the O2 sensor "out of range".
This happened with every O2 sensor I had >I recently acquired a 1990 325i with 191000 miles on it. It is in very good
The air filter is contained in the big black box behind the left headlight. There are several clips around the perimeter of this box that have to be unsnapped, and i can't remember if you have to remove the airbox to get it separated or if you can leave it in place and remove the upper portion. Whichever it is, it's real easy and obvious once you get in there to do it.
The check engine light is telling you there's something wrong (probably minor - don't worry). Usually it's a vacuum leak or a small rip in the rubber air intake boot or maybe even just a bad seal on the dipstick or oil filler cap. You don't need to take it in to get the fault codes checked - with the E30 325i you can do it yourself with the ignition key and your foot on the gas pedal:
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