05 taurus rough idle when cold then runs fine. code P0308 was pulled. No other issues, car runs great beside that. I know 308 means multi cylinder cross fire. So it has to be something common to all cylinders?

Believe this is random misfire codes. Have ignition module tested at parts store.

Code 308 means cylinder 8 is not producing power.
Could be something mechanical, electrical, or fuel related.

misfire can be from plugs and also from injectors. It it is fine when it warms up I would be looking at injector tip problems from the cold.

spark plugs work better when theyre hot so change spark plugs,

Idles rough and quits when gas pedal is pressed less?
http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html
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Rough idle, staling and Erratic shifting?

http://technoanswers.blogspot.in/2012/03/rough-idlestaling-and-erratic-shifting.html

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Its a hot start issue.

Can be related to low fuel pressure or problem with crank sensor.

Also it can be weak battery or starter.

But possibilities are to be inspected to confirm what exactly it is.------

To troubleshoot and confirm the issue,i suggest you refer few solved help links with similar types of problem like yours:------

Click the link below:------

1991 Toyota Trecel: Engine Starts fine but dies when gets Warm?

http://whatisbyme.blogspot.in/2012/05/1991-toyota-trecel-engine-starts-fine.html

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1994 Toyota Pickup: Starts fine but dies in few seconds?

http://howtobyme.blogspot.in/2012/05/1994-toyota-pickup-starts-fine-but-dies.html

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1995 Lexus LS400: Running Hot?

http://whatisbyme.blogspot.in/2012/05/1995-lexus-ls400-running-hot.html

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2002 Toyota Camry: Puff of Blue or White Smoke while Starting?

http://whatisbyme.blogspot.in/2012/05/2002-toyota-camry-puff-of-blue-or-white.html

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Multiple problems on car: Car runs hot, A/C blows hot and car starts surging?

http://schematicsdiagram.blogspot.in/2012/04/multiple-problems-on-car-car-runs-hotac.html

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Delay starting on Toyota Prius?

http://schematicsdiagram.blogspot.in/2012/02/delay-starting-on-toyota-prius.html

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Honda car will not start intermittently?

http://technoanswers.blogspot.in/2012/02/honda-car-will-not-start-intermittently.html

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Vehicle Starts, Runs and Loses Power

http://whoisbyme.blogspot.in/2012/07/vehicle-startsruns-and-loses-power.html

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Intermittent starting issues on Volvo 760?

http://schematicsdiagram.blogspot.in/2012/02/intermittent-starting-issues-on-volvo.html

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Car starts and cuts off immediately?

http://repairhelpcenter.blogspot.com/2012/01/car-starts-and-cuts-off-immediately.html

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Car won't start when cold?

http://schematicsdiagram.blogspot.com/2011/12/car-wont-start-when-cold.html

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These details will help.

Thanks.

It can be issue with IAC( idle air control valve) causing the problem.

There are many other possibilities causing these idle issues.Engine idles rough.

There are few help links with solutions to troubleshoot such idle issues.

I suggest you refer the link below and follow its troubleshooting details:------

Click the link below:-----
Bad miss at idle? http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

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Stumbling and stalling at idle after engine rebuild?

http://schematicsdiagram.blogspot.in/2012/03/stumbling-and-stalling-at-idle-after.html

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1999 Ford F-150 Idles rough and quits when gas pedal is pressed less?

http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html

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Engine stumbles coming off idle when warm?

http://repairhelpcenter.blogspot.com/2012/01/engine-stumbles-coming-off-idle-when.html

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Erratic idle on car?

http://schematicsdiagram.blogspot.com/2011/12/erratic-idle-on-car.html

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Cold start problem and vehicle shudder around 2500 to 3500 rpms
http://repairhelpcenter.blogspot.com/2012/10/cold-start-problem-and-vehicle-shudder.html

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Low idle when cold out side?

http://repairhelpcenter.blogspot.com/2011/12/low-idle-when-cold-out-side.html

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GMC Sonoma Stalls and idles low

http://technoanswers.blogspot.com/2012/10/gmc-sonoma-stalls-and-idles-low.html

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GMC Idle Air Control (IAC) Valve Replacing?

http://schematicsdiagram.blogspot.com/2011/12/gmc-idle-air-control-iac-valve.html

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1996 Camry intermittent engine failure while idle?

http://repairhelpcenter.blogspot.com/2011/10/1996-camry-intermittent-engine-failure.html

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Engine quits at idle?

http://repairhelpcenter.blogspot.com/2011/10/engine-quits-at-idle.html

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Car overheats and Air blows hot at idle?

http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html

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High Idle Problem

http://repairhelpcenter.blogspot.com/2012/10/high-idle-problem.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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Idle flair is noticed on car? Rough idle? car will not idle? Erratic idle speed?

http://technoanswers.blogspot.in/2012/02/idle-flair-is-noticed-on-car-rough-idle.html

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High rpm in neutral? Inconsistant high RPM in neutral?

http://technoanswers.blogspot.in/2012/02/high-rpm-in-neutral-inconsistant-high.html

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Vehicle stumbling at idle and shows code 54?

http://schematicsdiagram.blogspot.in/2012/03/vehicle-stumbling-at-idle-and-shows.html

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Rough idle, staling and Erratic shifting?

http://technoanswers.blogspot.in/2012/03/rough-idlestaling-and-erratic-shifting.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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These details will help.

Thanks.

There re few possibilities that can cause no idle issues.To troubleshoot the issue help links are provided below.Click the link below:---
Idle Problem? http://whatisbyme.blogspot.in/2012/05/2001toyota-corolla-idle-problem.html
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Idles rough and quits when gas pedal is pressed less? http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html-----------
Stumbling and stalling at idle after engine rebuild? http://schematicsdiagram.blogspot.in/2012/03/stumbling-and-stalling-at-idle-after.html

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Cooling fan Shuts OFF and Idle Drops? http://howtobyme.blogspot.in/2012/05/toyota-celica-cooling-fan-shuts-off-and.html

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Rough Idle and Vibration? http://whatisbyme.blogspot.in/2012/05/2006-ford-f150-rough-idle-and-vibration.html

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Steering Wheel Vibrates at Idle? http://whatisbyme.blogspot.in/2012/05/1993-toyota-corolla-steering-wheel.html

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Runs Fine But Idle Is Low? http://whatisbyme.blogspot.in/2012/05/2004-toyota-highlander-runs-fine-but.html

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Vehicle Will not hold Idle? http://whatisbyme.blogspot.in/2012/05/2003-lexus-es300-vehicle-will-not-hold.html

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Engine Idles Rough and Dies? http://whatisbyme.blogspot.in/2012/05/1994-lexus-es300-engine-idles-rough-and.html

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This will help.
Thanks.

find a code book and replace the bad sensors and then check your codes after resetting the computer

remove neg. cable from battery so the ECM will reset this may work. make sure the IAC is air tight. if this doen't fix your problem have someone check the IAC valve if it's bad the part runs $300.00 pluse

p0308 is cylinder 8 missfire, it could be the plug on that cylinder,wire, or coil. also make sure the injector for that cylinder is ok!! have a good day!