Rough Low Idle Only When Foot Is On Brake? Rb26

[nakameguro]

Hey guys,

last night my r32 gtr started idling roughly, bouncing between 600-900rpm. this is in neutral with my foot on the brake pedal. when i lift off the brake the idle goes back to normal?

the car never stalled, and once driving the engine runs super smoothly. sometimes the rough idle would sort it's self out and then come back again a bit later.

how would my foot on the brake cause the rough bouncing idle?

cheers for your help!

[GTofuS-T]

Vacuum leak, check all the vac hoses coming off the break booster

[89CAL]

I would say an internal leak in the brake booster, if it was the hose it would leak all the time

I would listen around the brake booster for a leak anyway. Sounds like the most likely cause.

[Ben C34]

I would say a leaking brake booster.

[GTRPSI]

Strangely if the master was leaking a little the RPMs should have gone up, not down......well it did when my clutch master was leaking from a broken diaphragm, you could hear a hiss when you pressed the pedal and RPMs went up.

Then again if the rip in it is large enough, it would be like a AFM not connected and run rough.

[nakameguro]

quick update on the issue.

I drove the car today and it idled perfectly. Then when i drove home in the evening it was doing it again. I realised it was only doing it when the headlights are on, so it seems to be an electrical issue, and linked to the extra power usage when the brake lights come on while headlights are on? could this mean it's an alternator on it's way out? or something else electrical?

cheers

[89CAL]

I see. Got a multimeter? If not borrow or buy one and check voltage with the car running. 13.5v - 14v is about what you want to see at idle

Start there anyway. Report back

[nakameguro]

Cheers guys.

I took the gtr to a Nissan dealership and they confirmed that the voltage coming out of the alternator was a bit low, but because I'm running an aftermarket ECU they can't confirm that's the only issue. Also they said they wouldn't touch my car unless I changed the cars ECU, cat, back to stock, and put wheels that sit inside the guards on.

So I've organised an independent shop to replace the alternator this week. Hopefully that will resolve the issue.

Cheers for the help

Edited January 16, 2016 by nakameguro

[75coupe]

Why do people take their skylines tonissan for repairs???

I wouldnt even take my 2 yr okd navara to nissan unless it was for warranty

[Hadouken]

Lol at Nissan saying put it back to stock.

Good luck with the alternator, I reckon you have vac leak

[Ben C34]

Put back to stock and let Nissan fix it.

[Ben C34]

Poking out wheels will affect Nissan's ability to work on your cars engine.

[Ben C34]

How much did they charge you?

[breaker1845]

All car dealers are actually useless with repairs and will avoid responsibility for anything.

Probably $100+ just to probe the alternator with a multimeter to get a reading.

I'm more inclined to think it is a vacuum leak.

[tridentt150v]

Its the cat......everybody hates cats!!! get a dog!!!

[nakameguro]

Hey guys cheers for all the feedback. Actually nissan in japan have been pretty decent, they have been good for ordering new parts, even sending some of them to me free of charge. they didn't charge me anything to look at it the first time, but as i said they wouldn't work on a car with this many mods.

In an attempt to save time and make life easier i opted to have my other shop just change the alternator without doing further testing. Unfortunately the problem was still there when i took the car, so in the end i had to take the car back again. turns out the issue was a poor ground to the battery which they fixed, and he found a separate issue with my headlight high beams which he also fixed. as they felt bad i had just replaced my alternator for no reason they didn't charge me for the extra work.

so now the car runs sweet again.

In the end I paid about 500 squid AUD (damn the weak aussie dollar) for the new remanufactured nissan alternator fitted. (nissan would've charged me about 650 for the same work).

Edited February 13, 2016 by nakameguro