Rb25det Low Idle And 'bubbly'

[anthonymcgrath]

hey guys

I've a bit of an issue I hope you can help me with. I've seen a few threads on here and done some swotting up (one guy reckons fuel pump) but I thought I'd post up what mine is doing and what I've replaced to get a clearer picture

it started about a month back - the car has progressively dropped rpm's on idle and now idles around 500rpm/+-50

If I fired up the car and it goes into cold idle it sits around 1500 or higher depending on what I'm asking the car to do (ie: get in and drive off, or let it warm up sat still)

however once the car is warmed up I can approach lights and the rpms will hold ok till the car is stopped then it'll dip very low - around 500rpm. the car will shake slightly, and its popping n bubbling quite a bit too. I find myself pressing the gas pedal a touch to keep the revs up.

I dont have aircon so as a test a friend said to switch the aircon button on... this makes the rpm climb to 900 where it should be but the popping n bubbling is still there - at least it doesn't feel like it will stall tho.

on normal driving and full power its brilliant - no issues - holds its boost all the way - chased a carrera 4S up the road and found myself backing off a bit.

I've put in:

-NGK plugs iridium8's (car was mapped on them and the guys said it needed them with the td05 18g under the bonnet making 1.4 bar)

-new coilpacks uprated (Rising Sun Performance who are well recognised skyline tuners here in the uk)

-new 02 sensor

-swapped CAS - no difference

-swapped Z32 AFM for another - no difference

-checked for boost leaks - none found

-fitted a grounding kit recently too (didn't expect that to make any difference tbh)

so I'm a bit scuppered now really... I have no idea whats causing this. My mate says his has done it for the last few years but I just cant live with it doing this - it has to be a fixable issue and I really wanna get it sorted.

any help would be massively appreciated!

thanks

ant

uk

www.anthonymcgrath.co.uk

[Wacky Dee]

I'm no expert but I've experienced the same sort of symptoms as you .. in my case it was the gap on the spark plugs ie. it was TOO LOW.

Also from what I remember, iridiums + skyline = what you are seeing. I don't see why you couldn't use copper NGK, just colder type like 8s. Don't change the factory (1.1mm) gap unless you get missfire, then try going down to 1mm, test again, then .9

1mm was the sweet spot for my car where it stopped the weird shaking and 'bubbling' type of sounds that I got with 0.8mm spark plug gaps.

[defari]

check your iac, may need a clean

there is a write up somewhere around this site.

[anthonymcgrath]

hey guys thanks for your replies

wacky - I had this bubbly lumpy idle before I changed the plugs so I dont think it will be related to those. I swapped them out for some iridium 7's gapped at 1mm. The lumpy idle was still there and also at higher rpm they wouldn't hold up and I got the classic misfire. I Tried regapping them. Did nothing. Then I put iridium8's in gapped @ .8mm and on med/hi boost its been great again but I've had the lumpy idle throughout no matter what I did with the plugs.

I'll give my AAC valve a clean tonight defari - I've done this in the past on other skylines but not on this one yet so I'll try that.

[Wacky Dee]

Try coppers ..they cost next to nothing and it's an easy DIY in under an hour. Leave them at the standard (1.1mm) gap before going lower. If you're making more than 300kw use 8s to be on the safe side, but regardless try the copper NGKs.

I am NOT 100% sure but I believe I've read before about iridium plugs and skylines simply do not play well with each other.