We've got this 84 240 sedan. It's got what I understand to be the "old" style (expensive) cast aluminium air mass meter.

When we got the car, is was said to have a bad airmass meter and it was replaced witha " good" used one. It made it home OK, but seemed to run a touch lean - slight hesitation when we stomped the gas pedal.

Now, it starts right up, but seems lean - it tends to backfire a bit till warmed up. Once warmed up, it idles fine - but there seems to be an rpm range (probably between about 1200 - 1800 rpm, where it will stall out completely for a bit, and when the rpm come back down near idle, it kicks back in and it keeps running. (it never dies completely). If we drive in in low gears, and keep the rpms up - it runs fine, plenty of power, it never misses. But in "normal" driving - it cuts out all the time.

Any ideas here? Ive not checked fuel pressure or anything, but the fuel pump sounds nice and quiet. I do believe its a fuel related issue. If I hold the fuel line (feel it) I can feel vibration from the injectors firing. When it misses -that vibration in the fuel line goes away - so I believe the injectors may not be firing, but not sure. I wonder if these have a throttle switch which could possibly have a dead spot? (like in the old old fuele volvos from the early 70's).

any thoughts would be greatly appreciated! Im hopeful its something simple... hopeful it's not the airmass meter because I think they are rare and expensive.