Rough Idle After Plug Change. Rb25det

[NateR31]

So i change the sparky plugs on my rb25det today cause she was missfiring all over the place at high-rpm, the plugs are gapped to 0.08, the car drives fine, no misfiring at all, and runs smooth as hell when not ideling, but at idel it sounds like a lump v8, and on the boost guage the VAC section jitters around. I checked back under too see if i forgot to plug a hose in and everything looked fine, could the plugs not all be gapped the same? u checked them all with a feeler gauge and they seemed fine! What else could it be? I have a slight hole in the end of my exhast but i dont think that has anything todo with it!

Nate

[carl h]

try opening the plug gap back up to 1mm, from what i gather the smaller the gap the worse it will make the car idle.

[NateR31]

try opening the plug gap back up to 1mm, from what i gather the smaller the gap the worse it will make the car idle.

<{POST_SNAPBACK}>

do smaller and larger gaps have any performace differences? cause the plugs that were in there were 1.1 and since i upped the boost it started to missfire, plug on cyc 3 was completely borked

[jazza08]

From my limited knowledge on the subject, if you up the boost the spark plug gaps need to come down, so 7psi may be fine with 1.1mm gaps but say 14psi would need atleast 0.8mm. Yes the smaller gap will perform slightly less but is needed to run higher boost.

In regards to why its bad on idle not too sure on that one...

[carl h]

no, gapping the plugs down is just a super ghetto fix for ailing coils, so unless you are blowing out spark (ie: high boost) then they should be good where they are.

i gapped my plugs down to .6mm and ive got a new set to go in that will be set at .9mm.

[SimonR32]

i had a set gapped to .65mm and they didnt miss

chucked in a fresh set at .75mm and now the new ones miss

so they are going to have to come out and get gapped at .65mm again

it does cause the car to miss a bit on idle

[jazza08]

Ye but ur running 17+psi right Simon? You'd need smaller gaps than say his high boost which would be 1bar??, on a stock turbo...?

[33SOM]

Ok not meaning to hijack here but my car sounds like a wrx when its idling but fine once the revs are up. I know it aint plugs or coils.

I changed my intake manifold back to a standard one and its hapened since.

What could it be??

[NateR31]

well, somone pointed out that they forgot to plug in some hoses, now my boost guage isnt reading vac, so i must of missed somthing, or somthings leaking, ill have to check it out..

Its not like it sounds horrible and the car is jerking around, sounds like a lumpy v8 and its kinda annoying