Cold start splutter

[XStatic64]

Hey all,

Just recently bought a r31 skyline with of course an rb30.

In the mornings when it is dead cold or hasn't been started up for many hours it runs like a pig, won't rev past 3k and sputters.

If you have it in drive you can pin your foot to the floor and it just won't rev or go anywhere.

But if you leave it to idle or give it a slow rev in neutral for a while (like a minute) then it's fine.

Any thoughts? I have a spare fuel filter here which i'm going to swap out. and a new set of spark plugs,

I have changed the oil/filter and thats about it so far.

[XStatic64]

Obviously this being a VL forum, i know this post is out of place but I'm sure there is an rb30 guru here who can shed some light on this fault.

[87RB30VL]

Maybe wait for the engine to heat up, which you normally have to do for any car? Or if it has a manual choke, hole it out for a few minutes until the revs settle, I have to do that on my 1983 Ford Courier Ute if I haven't run it in a while, until the engine heats up then it's fine.

[XStatic64]

It has a rb30, same engine as the vl, so no manual choke.

I have been told it could be the AFM. It does run alright after you let it idle for about a minute so it's no big deal.

I think I'll see if i can change the water temp sensor, afm, spark plugs and fuel filter and see how it goes though.

[detox_nath83]

Its Injected so no Choke..

AFM would b my first guess. Try one of a mates car if he got a VL or R31 can cause this man

Also your TPS (Throttle Position Sensor) could b failing

could b your CTS(Coolant Temp Sensor) until it picks up some temp and leans out your Fuel Mixes it settles.
soulds like its going into a "limp home" feature not revving past 3k but i would lean towards things i have stated..
Goodluck man

[XStatic64]

Thanks Nath,

Just put a new coolant temp sensor in today, have found the plug for it was stuffed, I am told an injector plug can fit with minimal modifications so will be on the hunt for that at the wreckers in the future.

Took the throttle body off today to replace the spark plugs too, checked all the wiring for the TPS which looked okay although as you say it could be the problem.

Will see if i can borrow an AFM, or i might even just buy a new one (2nd hand), theyre only about $50 privately.

Thanks for your thoughts.

[detox_nath83]

yeah these arnt really a visual inspection parts. the TPS and AFM that is... temperemental man.

dont need to take the throttlebody off to change the plugs u can get in with a uni joint on your extension

[XStatic64]

Yeah i know, but i spent way too long trying to get the plug lead out on that angle and thought fk it, 10 minutes later the offending 2 plugs were changed out. Easy Peasy.

Accidently left the radiator cap off, and may have let air into the cooling system when taking the throttle body off as i took the coolant line off there... The radiator opening was bubbling and looked like it needs a flush!

I have my money on blocked cat, so will drive the car around to my mates place next weekend and we're gonna push a pipe through it, as until i get it running 100% I'm not going to go and get the exhaust done on it.

Once its running good -- the price you can get 2nd hand headers for, I might even put a pair on while i sort out the manual conversion (reluctant to turbocharge it when it's got an automatic in it, as i know i'll blow it up)

Is the TPS an easily replaceable part? can just go to the wreckers and unbolt one right?

Cheers

[detox_nath83]

yeah man easy replaceable part but u may wanna try one b4 spending, to c if it is the problem. blocked cat will make the car really sluggish with no power. as u said unbolt the cat and bash it out if the ceramic internals are broken, but remember its illegal if u put it back on once bashed out.. but hey what VL has a good cat LOL

for your cooling just top her up and run your car take out the first (Lower) bleeder bolt near your temp sensor(rad cap on). and let air bleed out... then tighten lightly and undo your top bleed bolt on the plenum chamber and bleed it..
then top up cooling system again and repeat process... even good to go for a short drive to loosen any bubbles and do it again..

[XStatic64]

Alright so, I replaced the coolant temp sensor and the plug as the wires were frayed. Re-soldered a newie from the wrecker and put a new sensor on.

Cut the rusted rear muffler out too, it sounded like sand when you rolled it around, terrible!

Bled the coolant and topped her up

After it was warm, took it up the road to the servo, had a bit of a spirited drive back and it has some really good pickup for a N/A inline 6. I reckon it's probably pushing about 85-90rwkw atm.

Unfortunately when cold I unplugged the AFM (was told it will go into limp home mode wont rev over 2k) but it sputters and pops still, very odd. So currently still an issue.

[XStatic64]

Going to go to the wreckers tomorrow and see whats around, maybe i can find a tps for it to replace it.

[XStatic64]

Think i fixed it, wil have to see when it is dead cold again..

Air Regulator - R31info

It may have been this all along. Just unscrew the bolt, slide it towards you and enlarge the hole, voila!

Still unsure as the car had been run in the last 2 hours but will see tomorrow morning!

[detox_nath83]

if your car starts with the afm unplugged.. the afm is stuffed or starting to fail... if the afm is unplugged and u touch the throttle it will die straight away.. the ecu does not know how much air to measure to fuel and stalls...

[XStatic64]

I was told that if you unplug the afm it wont rev past 2k and goes into limp home mode.

EDIT: Also, the above air regulator fix actually corrected the issue. It no longer sputters on cold start and revs fine, runs well now.

And it did die the same as it was previously with the AFM unplugged, so we plugged it back in.

[detox_nath83]

unplug it c how u go... she will die as soon as u touch the throttle... ecu has no idea on airflow and stalls