I dynoed my car last week and I found out that I have a missfire at 5700rpm just to give you guy s and idea it has problem starting worst when the car is cold and now when I am braking the car stalls the rpms drop and drop until it stalls any ideas what could cause the problem? Spark plugs? Coils? Spark plug wires?

 

Most likely a vacuum leak.

 

no vacuum leak whatsoever

 

Yes, Yes and Yes
Change all, your plugs are good ones. Coils look extremely easy to change yourself.
Service history of them?


Missfires Can Be Caused By a Million and One Things,

Vac Leaks
Wiring Issues
Spark Plugs(Even Fresh Spark Plugs That Are Crappy Quality.... E3 And Such)
Ignition Coils
Alternators (Search EMI)
MAFS
Injectors
Injector O-Rings
Intake Gaskets
TB Gaskets
PCV Hoses
PCV’s
Malfunctioning EGR
Malfunctioning CAS
O2 Sensors
Aftermarket Intakes
Intake Hoses
Vac Lines
Timing Chains
Timing Chain Tensioner
Broken Cam Gears
Malfunctioning Cam Sensors
Incorrect Crank Gears(The I4 Has Like 40 Different Configurations For Whatever Reason)
Incorrect PCM Flash
Issues Within The PCM
PCM Wiring
Bad Diaphram Within The FPR
Issues Within The Fuel Pump
Dirty Fuel Filter
Dirty Fuel Lines
Pre-Cats/Poor Exhaust Flow

If the above gaskets/seals have not been changed, change them. Clean your MAF sensor, throttle body.
Change your PCV valve and probably that short hose as well.
Inspect the intake accordian tube for cracks. Inspect for vaccuum leaks.
Put in a good Fuel system cleaner: http://www.redlineoil.com/product.aspx?pid=80&pcid=12
Inspect wires. Re-set ECU after doing above.

 

Will begin changing spark plugs for the NGK Platinium ones next will change spark plug wires if that doesnt adress the issue then will check coils and so on I believe the wires and coil are from factory time to do a tune up

 

I thought i read you had NGK iridium plugs, but i don't see it anymore.
I have NGK iridium plugs (NGK iridium # TR5IX, # 7397, .6mm tip for my 2006 V6 ---- "NGK Iridium IX® offers extreme ignitability, improved throttle response and superior anti fouling") and they are great, preferred by modders.
I would definitely stick with NGK. With your car being so old, I would not hesitate to change coils, boots, plug wires, along with new plugs while you are there.

Iridium is the best of both worlds. Even though iridium itself isn't the best conductor, it's extremely hard. It'll last the longest of any spark plug tip material (some are rated up to 100K). Being so hard, the tip can be made to a fraction of the size of a normal one. This creates a very concentrated spark in comparison, which easily negates the lower conductivity of the metal. Iridiums are know to ignite lean mixtures that other plugs can't, which would definitely help fuel efficiency.
Iridium is more resistant to corrosion/fouling than steel/nickel electrodes and all-around tougher than platinum.
Platinum and Iridium plugs perform at a lower level than copper spark plugs, because they are less conductive and they tend to overheat. However, the overall longevity of these two types of metal is better than copper plugs. In reality, copper has the best performance of all three and the worst longevity. Platinum has good longevity and the worst performance. Iridium has good longevity and a performance that is decent, which is why iridium plugs tend to be more expensive than any other type. Still, the difference between these plugs in terms of overall quality is minimal, as there is a trade off for each.
Most copper plugs need to be changed every 20,000 miles or so. Platinum and iridium plugs can often go for twice that before they require changing, but the overall performance will not be as good and you may have to deal with overheating of the plugs. This is potentially not worth the added cost of both platinum and iridium spark plugs, although the decision will depend upon your preference.

NGK's Iridium IX Spark Plugs are designed with a tapered cut ground electrode. This new shaped electrode serves two purposes. Firstly, it allows for a better spread of flame during combustion. Secondly, in conjunction with the 0.6mm diameter centre electrode, it helps reduce the electrode quenching effect.

NGK PDF on different iridiums: http://www.ngksparkplugs.com/pdf/DYK...idium%20IX.pdf

Using Iridium has allowed NGK to reduce the centre electrode diameter down to a mere 0.6mm, increasing the performance of the plug, while at the same time maintaining an excellent service life.
In comparison Platinum centre electrode diameters are 0.8mm.
Iridium IX plugs increase performance by increasing the spread of flame in the combustion chamber.
FROM: NGK Spark Plugs Australia

 

Well changed the plugs and let me tell you they looked really bad well glad I did that. But the stalling problem didn't go away instantly I began to play with the Idle screw and wala no rpm dropping. About the missfire I am not sure I think I will have re dyno the car again

 

Misfire at that rpm, is the wastegate operating open full, or leaks? i know it would be difficult to check, but at that rpm, only?

 

Where the plugs fouled? You say looked bad.

 

Have you replaced the fuel pressure regulator (in regards to stumble/low idle)?