E30 Zone

Hi
89 318i M40

I thought I'd be clever and replace my air intake rubber pipe but in doing so I have mucked up my idle.

It used to idle at 800 revs, but after changing the pipe it now idles at 1500.

The idle is steady, just high. The pipe is on properly and there are no leaks that I can find.

It seems like I have disturbed something but I don't know what.

Any ideas?

have you moved the throttle cable ? try winding it in till the revs drop

I tried that but it didn't seem to do anything.

Strangely it now idles at 900 after starting but as soon I have driven anywhere it idles 1500 or so.

have you got the new boot on properly?

check that you haven't folded the lip on the underside of the throttle body or afm .

have you knocked a breather pipe off?

Nothing looks like its missing and the pipe is on properly.

Have gone back the old pipe and still idling high.

The haynes mentioned the TPS but I couldn't work out where it is or even what I'm looking for. A plug is fairly obvious but there are a couple around the throttle body. May just check them all.to be on the safe side

What does the tps look like?

I've had another good look around and everything looked properly connected. I cleaned the connector directly below the air intake but still had issues.

In the end I adjusted the throttle stop screw thing which brought the idle down. It drives nicely and the revs settle down properly when I stop at junctions.

Although it now seems sorted it still seems weird that changing the pipe mucked the idle up even when I put the old pipe back on.

At least it's sorted now. Thanks for your help

blimp wrote:In the end I adjusted the throttle stop screw thing which brought the idle down.

Unless some previous owner has wound in the screw in an attempt to 'cure' some other fault, you have NOT 'sorted' anything - you've just introduced a second fault that is counteracting the original one.

Of course you are correct Brian. Technically I've got myself a workaround which of course just sorts out the current symptoms and does nothing to sort out the true cause.

When I've worked out what the TPS look s like and where it's hiding I'll try and pinpoint the root cause (apart from me fiddling)

I also did notice that the cap on the afm mixture adjustment screw was missing, so I guess there is a chance that it has been fiddled with - the car had no history when I got it (which I feel like I'm coming to regret)

TPS is right on the bottom of the shaft for the throttle butterfly, but before you can adjust that correctly the throttle stop that you have 'adjusted' has to correctly set.
AFM screw can only be correctly set by connecting the exhaust to a gas analyser, but this can only be done with an otherwise correctly working engine.