Help M20 Sputtering and Popping.

[BritishMike]

So last week my 325is developed a sputtering problem around 3000 rpm. After some internet digging it seems this isnt an unheard of problem but one with 20 different solutions. So I attempted some of the more basic things. Ive read about a vacuum leak or something wrong the it o2 sensor so made sure I didn't see any cracked hoses and all clamps were tight also dropped the negative lead off the battery for 15 mins. Jumped in the car started right up Went down the street now the sputtering is exponentially worse its pretty much from 1500 on and is a lot more violent also popping through the exhaust I don't understand what could have caused the change. Any ideas?

-Mike

[ak-]

It's miss-firing. Check spark related items.
My guess is a bad distributor/rotor. Replace them anyways as it's part of regular maintenance.

[BritishMike]

I guess I just don't understand how that amplifies from un hooking the battery.

[jeffnhiscars]

I guess I just don't understand how that amplifies from un hooking the battery.

The ECU goes through a learning curve and has volatile memory (meaning without power it loses it's data). You reset it.

[BritishMike]

So how long till it re learns and stops running so harsh?

[dnguyen1963]

It should take only about 10 min of driving around for the ECU to relearn.

[E30NJ]

what spark plugs do you have?

[Lugnuts]

I've disconnected my battery and swapped ECUs around and the engine has always fired right up and driven fine. Admittedly, I'm talking about swapping between 153 and 173 Motronic. Never had the engine bucking and spluttering afterwards. She tends to idle a bit high initially, but that's about it.

Check your Crank Position Sensor resistance - 540 ohms +/- 10% across pins...1 and 2. Check directly at the connector next to the intake manifold and from the ECU harness end. Just resolved an issue with mine and in the process tried a ghetto CPS spliced from an old and new and boy did she not like that - very uneven at anything above 1500 RPM.

Also, check the state of your CPS...remove, clean and remount.