At last we're bringing back to life our 1987 740 Turbo, B230ET engine, which we've had in the family since it was just about brand new. It's not run properly on the road for years, and not run at all since 2021. So of course when I put a new battery in, and fired it up last week, there were some problems. Most of these I've sorted - BUT.... Anyone have any suggestions for why from cold at idle the engine is chugging badly and misfiring, not so evident at about 3,000 revs, but at idle is so very bad? I have now put in new plugs, new dist cap, new rotor, new injection relay, cleaned up all the connectors on the injectors, new coil, and all the leads checked, checked the MAF meter for dirt and function and put in a new air filter, checked everywhere for airtightness, and so on. Ran the engine for 10 mins to very warm/hot, hoping it would kind of sort itself out and run smooth, but it did not. Still chugging and shaking at idle, less so when upping the revs. Accelerator peddle seems only to kick in when around half-way down, so I have been increasing the revs by hand in the engine bay. So in short, misfiring at idle/lower revs, accelerator pedal mostly not increasing the revs. Very rich exhaust output (lucky neighbours) - presumably because of the misfire. Anyone any ideas??

 

Have you checked the timing? The belt might have jumped a tooth or two; that could cause the rough running at idle, and cause it to be less evident at higher rpms

 

Thanks - excellent suggestion, makes sense. I'll ask around to see if any mobile mechanic can replace the timing belt and ancillary bits, while the 740 is not running and is off the road. Not something I'd like to tackle myself.