I have been running my car lately and it seems to iss slight at idle and a lot between the 2-3 thousand and 5 an up thousand range. Anywhere else and it doesn't miss at all. I just replaced the spark plugs, cat and fuel filter. It missed mroe often after i installed the fuel filter.
Anyone else have this problem or know how to fix it? Thanks.

Just a question....but when's the last time you replaced your cap and rotor? Could be lots of things, but that's where I'd look first, as it's a general maintenance item anyway.

Originally posted by bmw325is
....I just replaced the spark plugs, cat and fuel filter. It missed mroe often after i installed the fuel filter....

Is this an M3 or 325i? What year?

Have you checked vacuum leaks, plug wires, in-tank pump (if applicable), etc?

JamesM

I just bought the car so i dont know when the cap and rotor were last replaced. It's a 1991 m3.

Could be a clogged in-tank pump filter screen or a dead in-tank fuel pump. All M3s had the older style gas tank with 2 fuel pumps. Other E30s from 1989+ came with a more updated fuel tank and a single, high pressure pump mounted inside the tank.

On the M3, remove the rear seat bottom and the black access panel on the right. Under there is the fuel level sender and the in-tank pump. Either jumper the fuel pump relay (behind the coolant reservoir) or start and run the car. Use a mechanics stethoscope or a long dowel pressed against your ear. Listen for a distinct whining/motor noise. Unplug the 2-prong plug. Does the noise quit or stay the same? If it quits, then the pump is running (Until you unplugged it, of course). If the noise doesn't change, then the in-tank pump is dead and causing you to lose fuel volume when you need it. If there was any rust in the tank, it is now clogging the pump screen.

Other things to check are vacuum leaks (do you have a poor/rough idle??), old, chafed plug wires, deteriorating ignition coil (heat is the enemy, and they live on the hot side of the engine), or possibly a worn carbon track inside the air flow meter.

One more thing--UNPLUG the altitude sensor. If it fails, it will lean out the fuel mix because it thinks you're at a higher altitude than you really are. Just unplug it and leave the wire dangling.

When I replaced the cap and rotor on my 166k mile-old M3, it helped dramatically. But then again, this thing looked like it was 10 years old, too. You never know! I also bought new OE-style wires from bimmerworld. They helped eliminate an intermittant ping at high RPMs, too. My wires were old and you could see the grey dust on the silicone jacket. That's a clue that the spark is leaking out right there and charring any dirt/dust/oil on the wires. Old wires on my wife's Mustang also caused a bad ping and loss of power. I would only buy GS Performance Magnecore wires or OE-style wires from bimmerworld/Turner/etc. Nology wires are a no-no.

JamesM

Alright thanks for all the help i'll check these things out. Also where is the altitude sensor located?

We found out the seal around the spark plug holes was bad and it was letting the oil from the valves getting in. This was causing a bad electrical connection so it missed. I cleaned them out and now it runs good.

Thanks for your help.

Originally posted by bmw325is
Alright thanks for all the help i'll check these things out. Also where is the altitude sensor located?
Right next to the airbox. It's a rectangular dome-shaped thingy. Unplug it and leave the wire dangling. If it fails, it will make the computer lean out the mix and BOOM, bye-bye engine.

JamesM

so are you saying it should be hanging or it should be plugged in?

Leave the sensor completely unplugged.

Do a tune up,then try using higher octane fuel.:dunno

HELLO THERE GUYS!
JUST WANTED TO INTRO MYSELF SINCE IM NEW IN THE FORUM! IM IN GREECE......BUT FROM CALIFORNIA!
I ALSO AM AN M3 E30 SPORT EVO OWNER!
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TAKE CARE.
RSM

how much are these chips?

I'd like some info too...and a dyno chart :D