Help!! High rev when stopped

[oakley]

Driving to work yesterday and had to jump on the brakes but as I stopped then revs went up to 3-4k and sat there- With my Schnitzer exhaust thats loud!!
What the hell coulda caused it? Same coming home I had to brake hard again and did the same thing-
Iv checked the usual my carpets are oem and so are screwed down and cant move (first time it happened I though i had caught he gas pedal at same time as brake pedal in my big clumpy work boots!!)
Checked and lubed the throttle cable and mech that moves the butterflys-cleaned the throttle body whilst there, .....
Any other ideas? After doing all this iv just taken it out for a hard drive and brake and it was acting normal but if u have any other ideas please shout em out!!

[angel318ti]

sounds vacuum related. maybe a loose line somewhere?

[BMW_Hatchback]

I second checking the vacuum

[thesk8nmidget]

yep vacuum is most common

[aceyx]

Originally Posted by oakley

(first time it happened I though i had caught he gas pedal at same time as brake pedal in my big clumpy work boots!!)

I do this all the time; the brake pedal has a greater offset from the firewall but if you're standing on it you're going to hit the accelerator as well. Kinda works to your benefit since it increases vacuum to the brake booster.


If that's not it, (after the vacuum lines) check your air intake boot. They're known for cracking over time, perhaps the sudden stop is shifting the engine forward enough to open a crack.

If that's the case, probably want to check into your engine mounts as well, there should not be that much play in them.

[lpcapital]

Originally Posted by aceyx

Kinda works to your benefit since it increases vacuum to the brake booster

Are you sure vacuum increases as you step on the gas... I think you have the max vacuum when the engine is idling i.e. the butterflies are close.

I'm not sure a vacuum leak could cause a surge in RPM. If you unplug any vacuum line you should notice a drop in RPM, not an increase. But you can try unplugging a small vacuum line or the break booster and see what happen.

I would guess it was the butterfly that was getting stuck open and by lubing/cleaning the intake you fixed it.

[oakley]

Yeah cheers people- I always reg check for any damage to the lines and cant see anything....I only cleaned the throttle body lasy week so maybe I cleaned it abit too much and it needed abit of lubricant and just got stuck!! Guess I just gotta keep an eye on it and see if it happens again!!

[lpcapital]

Oakley,
I am experiencing something similar on my Z3 M44: it appears the throttle gets somewhat stuck when it transition between the small and the large butterfly. So I was thinking about removing the TB and clean it.
Any tip?