Choking Beemer

Can you help with a long-standing problem with my 1987 BMW E30 325i? Between 1700-2500rpm, the engine seems to choke and you need to either give it extra throttle or apply the brakes to get over it. I’ve replaced the ignition, spark plugs, fuel filters and fuel lines. The air mass meter seems to work correctly and the fuel pressure is OK, as is the engine compression. Dick Brant

As this is a long-term problem and you have taken quite a few measures to rectify it, I’m assuming that you have checked the induction and vacuum hoses for leaks. If this has not been done, then this would be the first step.

Even though you can see the airflow meter door moving, this does not mean that it isn’t the source of the problem. You can get issues from a sticking door, in which case lubrication can help, but I suspect the fault may be internal. The contacts that move as the airflow door swings may not be working smoothly in certain areas along the track, resulting in an uneven feel to the drive. It may be possible to repair the unit by releasing the top cover, using an electrical cleaner on the track and possibly bending the contact slightly to increase the pressure. The top can then be refitted using a silicone sealer.

Not having felt the problem myself, I have one other thought, which is that the problem may not be engine-related, but rather due to the transmission. I’ve come across similar mid-range problems being caused by the Guibo (flexible disc) coupling between the gearbox and propshaft. Inspect the coupling for cracks, which may indicate that it’s failing.