Fast idle V8

[Tiger]

I had the engine replaced and everything transferred to new engine. The problem now is that the engine won't idle normally... it idles high at 1000RPM instead of 800 cold and like 500 when in gear. I suspect intake leak or some kind of leak that allows engine to suck more air than usual.

When you rev the engine, it also won't drop right back down... but gradually come down... so it could be like 30 seconds or so before it comes back down to high idle.

It is spring and I want to fix that car. This tells you don't trust anyone who is not a BMW specialist to swap out the engine. A freaking waste of money.

540 engine

[ahlem]

Possibly something simple like throttle cable needing a bit more slack or the cruise control cable needing more slack. Some times when you loosen up all that stuff to swap it over, you fracture the end of a vacuum hose or don't get a gasket seated just right. I'd try a trip through the vacuum system connections with carb cleaner. I just found the solution to an idle issue by locating a loose hose clamp. I felt like a dummy but didn't admit it to anyone. Is the idle steady and smooth?

[Tiger]

Not the throttle cable... it is loose... I checked. Idle is steady and smooth.

[Rustam]

it idles high at 1000RPM instead of 800 cold and like 500 when in gear. I suspect intake leak or some kind of leak that allows engine to suck more air than usual.

what is the condition and position of throttle position sensor? if it does not engage the idle circuit the engine computer will think gas is constantly applied. IF there is an additional leak into the plenum there is a fully simulated gas pedal push.

[Tiger]

Hmmm... I will check that TPS... before the engine swap, the TPS is normal. TPS is simply transferred over along with the intake manifold.

[Rustam]

yep. got to specifically insure that the idle signal functions properly.

[shogun]

you might also want to check your air temp sensor and coolant temp sensor. I once forgot to connect the air temp sensor and that also caused some trouble, actually the plug fell off the connector as I did not connect it properly.