My E30 jerks back and fourth quickly?

[RCFrEd12]

Hi all! I've bought my first BMW E30 318IS, and it's amazing! I have a question though. When I'm in first, second or most noticeably third and my foot is very slightly on the throttle pedal everything is smooth but then when i press down on the throttle a little more my car jerks around rapidly? Now I know it's a old car with 143K miles and maybe that's the way the gears and diff is designed? But then I put my foot further sown on the throttle and the jerking goes? Is this to do with transmission/diff or the engine itself? Maybe spark wires or plugs? Or is it normal?

Kindest regards,

Fred

[DesktopDave]

Welcome to the 'club. They are nice cars, aren't they?

Definitely not normal behavior for the M42 though. It can't really be the trans or diff, they're just two meshing gears...strictly mechanical.

Mid-range bucking is usually due to misfiring. It can be caused by a bunch of different problems, but I'd start with the easy stuff. How old are your spark plugs? How old are your wires? Have you checked the plug wells for oil? The cam cover seals can fail and let a little oil down into the plug wells. Moisture can collect down there too, but it typically dries out pretty quickly.

The other problem that can cause RPM-dependent bucking is a bad AFM. They're not the easiest thing to repair, it's usually best to find a buddy with a similar car, and swap stuff out until you find what's causing the problem.

You can also try the "stomp test", since our cars did come with a very rudimentary OBD system. If you do it right the car will flash the CEL to report problems. Google it, there's lot's of online guides.