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Misfire On Cold Start & Hunting Idle

Rekin

By Rekin,
in General Maintenance

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Rekin Grand Master

Rekin

Posted
Posted

Hey,

My car had just recently started to have a hunting idle.

My tuner decided to richen up the idle via Nistune and bumped the ignition timing electronically from 15deg to 20deg. This smoothed out the roughness of the hunting but it didnt get rid of it.

Ive also noticed that after increasing the ignition timing to 20deg I have a problem with cold start.

When I start the car up in the morning now and leave it to idle (ignition timing 40deg, fluctuates 41/42) I can hear it missing now and the car shuddering each time it happens. Idles remain 900rpm+ but can hear missing until i move off and warm up the car eventually.

Anyone know what the problem could be?

The car was running perfectly before the hunting idle began and richening the idle has just created more problems haha.

Although i cant understand how the rich idle is causing the car to missfire on cold idle?

Ill be cleaning the AAC valve on the weekend, but just wanted to know if there is anything else which might be causing the initial hunting idle?

Thanks

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Duff_man Collaborator

Duff_man

Posted
Posted

yeah i had a similar problem

My idol was fluctuating and misfiring even when hot

my wiring harness need to be fixed (not sure that was to do with this thou)

it turns out i needed to replace the:

air-flow meter

coilpacks harness (loom)

coilpacks

and a good tune

Rekin Grand Master

Rekin

Posted
  • Author
Posted
yeah i had a similar problem

My idol was fluctuating and misfiring even when hot

my wiring harness need to be fixed (not sure that was to do with this thou)

it turns out i needed to replace the:

air-flow meter

coilpacks harness (loom)

coilpacks

and a good tune

hmm

thing is i have a z32 afm, splitfires, and a tune done only couple of months ago and its started to act up now.

Im thinking it must be something really simple like a hose or something as the problem just popped out of nowhere...

  • 2 weeks later...
Rekin Grand Master

Rekin

Posted
  • Author
Posted

Update;

Ignition timing on idle dropped back to 15deg - Eliminated the misfiring on cold starts

Cleaned AAC valve, was pretty dirty.

My car occasionally starts to hunt. Anything else linked to hunting idle?

Thanks

mad082 Grand Master

mad082

Posted
Posted

you can still have idle issues even with a clean AAC if the idle isn't adjusted correctly. you need to put the ecu into base idle mode (pretty sure you can still do this with a nistune) and adjust the idle screw to the correct idle rpm. what happens is that if the idle isn't correct via the idle screw, the ecu has to compensate using the IAC and AAC to get it to the ideal rpm, which can sometimes cause the hunting even if they are clean.

Rekin Grand Master

Rekin

Posted
  • Author
Posted
you can still have idle issues even with a clean AAC if the idle isn't adjusted correctly. you need to put the ecu into base idle mode (pretty sure you can still do this with a nistune) and adjust the idle screw to the correct idle rpm. what happens is that if the idle isn't correct via the idle screw, the ecu has to compensate using the IAC and AAC to get it to the ideal rpm, which can sometimes cause the hunting even if they are clean.

Hey, yeah i did a similar method to fixing up the idle.

Warmed up the car and disconnected the plug going to the AAC Valve (Rb20's only, on the rb25's you disconnect the plug going to the TPS)

Then turned the idle screw to an idle of around 750rpm (recommended by tuner)

Car has its good days and its bad, sometimes it idles perfectly and some its all hunting and vibrating. Last time i had a similar problem was with the old o2 sensor. Although ive only done 10k on the new o2 sensor so i doubt that needs replacing again...

Next stage will probably clean the TPS but dont think that affects idle on rb20's...

  • 2 weeks later...
stormtrooper Proficient

stormtrooper

Posted
Posted

Hey, having similar issue at the moment in my 32 GTR. Every now and then when it's cold it'll idle rough and accelerate rough aswel until it gets a bit warmer (bout 40-50C water temp) but then it'll still hunt at idle and have to poke rev's at it to stop it from stalling.

I have Z32 AFM's aswel.

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