Stagea - Idle increasing when brake is pressed !

[Jay95R33]

Howdy fellow Stagea owners

A strange thing happend this morning when I started the car up.

Did the usual and let it warm up a bit before driving off but as soon as I pressed the brake lightly the revs increased from 1100 (cold) to 1500. Take the foot off the brake and the revs dropped back down to 1100 again.

Got to work and the car was warm. Normal idle is about 700rpm, lightly press the brake and the revs increased to ~1100rpm. And putting around the car park slowly in D I could feel the revs increase as I pressed the brake, so it does it in D and N/Park (it's an auto !!).

Strange... The first thing I thought of was an air leak in the brake booster or vacum hose going to it - but being at work I haven't had a chance to pop the bonnet.

Any ideas ?

J

[Happymeal]

Not wearing unusually big/wide boots are you? Sorry couldn't resist lol, seems very bizarre.

[Jay95R33]

lol - I've just got the normal clown shoes that I wear to work

But naa, nothing like that. Very strange hay.

J

[mcnamg]

that sounds weird but i have heard of this before my wifes ford fairmont used to the do the same thing couldnt for the life of me figure out what it was but once i flushed the brakes and fitted new pads all round and put new front discs on it went away. I would be very interested to find out what the problem is.

[Sydneykid]

Hi J, common problem, you just lead a sheltered life. Has the brake pedal effort increased noticeably since it started this? If it has, then it's a hole in the brake master cylinder diaphram, ouch not cheap. If the pedal effort hasn't increased (even slightly) then it's the one way valve in the line from the plenum to the master cylinder, it stops boost getting past. If the pedal effort has increased a lttle bit (maybe hardly noticeable) then it's the hoses/clamps, either the clamp/s will be loose or one of the hoses has a split in it.

Hope that helps, please let me know what it ends up being:cheers:

[Jay95R33]

Thanks for the replies guys.

This is the first auto I've owned, so I'm a bit nude when it comes to this wierd transmission stuff

OK, drove it home this afternoon (had the arvo off ) and it's stopped doing it which is good.

Another good thing is that the pedal feel/hardness hasn't changed a bit. Not even the slightest.

So I'm hoping that it's the valve in the vacume line to the brake booster or just a loose clamp. I took the AAC valve off over the weekend and cleaned all the crap out of it, and while I was doing it I was leaning and hanging off a few hoses, so maybe I've loosened one a little or pulled on it a tad to hard and cracked it

I'll give it all a good look over and post up how I go.

One other thing that I've noticed (and is the reason why I cleaned the ACC valve), is sometimes going from D to park (or even netural) the revs will hunt a little for a few seconds.

It sort of drops low then comes up and drops a little then then settles at normal. It's not as bad (or frequent) now that I've cleaned the crap out of the ACC valve, but still does it a little. Oh, and it has never done it when the air conditioner is on.

J

[C_DawG]

Isnt it completly normal for the revs to increase slightly when the brake pedal is pressed?

[Guest]

Mine has always had a funny idle and another Stagea that I know of, I was told from Japan it is hard to get a steady idle on the auto Stagea.

Just one of those things.

[Sydneykid]

Mine idles beautifully and the revs increase by less than 100 rpm for an instant when the brake is depressed and then it quickly returns to its nice stable 700 rpm.

[burkey22]

Mine idles funny aswell. Glad to hear it's not just me.

[Terminal]

Mine idles fine, and i just clocked over onto 110,000km.

My R33 used to idle weirdly, and i narrowed it down to faulty AAC valve or TPS swtich. same engine so maybe similar problems?

[Jay95R33]

Cool, yeah the funny idle only happens when you move the shifter from D to Park. Doesn't do it when moving from Park to D or when the air con is on. Appart from the funny problem yesterday, pressing the brake has no effect on the idle.

The 'idle increasing when the brake is pressed' hasn't happend since yesterday, so I think the valve just needs a clean.

I'll rip it out on the weekend and give it a hit of WD40 and brake cleaner

J

[BensDR30]

The idle on my RS4 occasionally drops to around 600 instead of the usual 700 (which makes it stumble when accelerating from a standstill). It has also been known to hunt between 700-800 when in N (like the AAC is oscillating). I think a clean-up might be in order....

It is perfectly normal for the rpm to flare slightly when depressing the brake - but no more than a few hundred rpm max. If you pump the brakes repeatedly you should be able to get the engine to hover around 1000rpm. It will then settle back down when you stop (handy for old cars that have dodgy chokes!).

[Russ114]

have you checked for leaks in and around the brake booster?

if the pedal feels normal, but pumping it increases engine revs it normally indicates a vacuum leak in the power assistance. It shouldn't affect your brakeing capacity, but might interfere with ABS and will rev the engine etc..

it could be something else, but from all the cars i've seen with a similar problem, it's normally a vacuum leak somewhere

[Jay95R33]

Thanks Russ,

I'm pretty certain it was just the check valve sticking a little. All is good now

J