Overrevving

[mike_h220]

When l start up 1986 420sl car is revving at 2000rpm and seems to want to climb, doesn't slow down when warm, any suggestions?

 

[Botus]

designed in choke fast idle
wrongly set up fast idle
mouse wedged in the mechanism and or eaten vacuum hoses
idle adjustment incorrect
not enough slop in the throttle cable
sticking butterfly
air leak
ignition timing too advanced

give things a clean, lubricate, check movement and set to std?

 

[mike_h220]

designed in choke fast idle
wrongly set up fast idle
mouse wedged in the mechanism
idle adjustment incorrect
not enough slop in the throttle cable
sticking butterfly
air leak
ignition timing too advanced

give things a clean, lubricate, check movement and set to std?

Engine slows down when in gear just revs high in neutral, will try cleaning and lubricating first, thanks

 

[Botus]

if its an auto, and you put in D or R of course the engine load will drag it back down... but it will use fuel, warm up things more and put a small bit of wear in the box.

if last time everything was right and no one touched it, and in D it seems normal and doesn't creep much more than it did, then likely a slight air leak.... (inlet gasket, vac hose, or such) if its trying to pull hard, linkage or something you need to fix soon

a small air leak isn't much of an issue if you drive gently, but long trips or ragging it - not so clever. you could try and listen and or use a liquid (maybe squirt WD40 round gaskets, injectors (if its got them)) and see if it sucks it in, it will likely change idle speed and if you go silly may want to stall doing that, and only use a small quantity (and don't bung it down the air intake). If it sucks it in and or the idle speed varies its a leak... of course mice eat things like vacuum pipes (to sensors, distributor vacuum, heater taps etc.) and that too can get you your air leak.... (just added this one to my original list - I'd forgotten that fun)