have a 1989 740.the car will not go over 15 mph.idles and starts perfect,floor the car and it races to about 2000 rpm then back to idle back to 2000 then idle.just rolls like this forever.i can close off the fuel return line and it reaches 2500 rpm.i have replaced the in tank pump,main pump,fuel filter,mass meter,spark plugs,temp sender,idle control valve,tps sensor,so what next please any advise? thanks

So when you "floor the car" it goes up to 2000 rpm then shuts down and starts back up to 2000 rpm over and over. Maybe it's a ECU problem. Mine jumps up to around 2000 rpm when first started then drops down the the normal idle speed. Have you tried increasing the rpm's gradually rather than flooring it to see what happens? Plugged catalytic converter?? Check the MAS plug for bad pins or broken connections.

when i say i floored the car i mean put the gas peddle to the floor.if i increase the throttle slowly it still races to about 2000 rpms then drops to 1000 rpms then back up to 2000 over and over again.very predictable.also i changed the fuel pressure regulator.also removed the o2 sensor to check for a blocked converter.the exhaust smells normal.you cant make the go over 15 mph.it feels to me like its starving for fuel.my next trip under the car i'm going to check for a crushed fuel line.the engine roll is so predictable you could set a watch by it.i have had a ton of 240's over the years driving an 89 240 with 372 k miles but this one has me puzzled.thanks for everyones help roy

Have you checked the OBD for codes? The very regular cyclic manner of the idle raiing and dropping sure sounds like an ECU intervention.....I might even swap one in if I had a spare...

Hello
It sounds like you are describing the ECU limiting an excessively high idle. If an uncontrolled idle reaches 2500 the ECU immediately steps in limits it. Is that what you are describing, an idle that revs to 2500 then immediately drops to 1000 over and over? What happens when you put in drive?
Kinda need more info.
Matt

Check the fuel pressure regulator, list details of exhaust smell, and post more details in general.
--
1990 740 Turbo, on its way to stock specs, maybe beyond