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2009 S5 4.2L Did a carbon clean put everything back in order. Started engine everything is running smooth I have zero codes in vag com. Take it for a test drive and it runs good until I hit 58-60 mph then the engine sounds like it’s misfiring with a lot of noise still no engine light and zero codes. Check misfire onVCDS and everything zero again. I changed plugs for NGK new mass airflow sensor and double checked all connections. And I have new ignition coils on the way. Any help would be very appreciated Thank You
 

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Had a recent misfire in 2010 4.2 and had to change all plugs and coils to clear it up. No issues since then. See what happens after you change coils. Also, how were the plugs when you took them out? How many miles on them?
 

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wow - those plugs lived 2 or more lives !
Mine were done around 45k the first time and actually the coil ruined one of the plugs but we believed the coils were the cause of the misfire issue. 65k miles now.
 

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I bought it used with 95000 on it and decided to do the carbon cleaning. Valves were very dirty. Car idles perfect it’s just when I get up to 58-60 mph I believe it’s misfiring a lot of noise and power loss. I put the new NGK plugs in thought it would run better but maybe it’s a bad coil
 

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wow - those plugs lived 2 or more lives !
Mine were done around 45k the first time and actually the coil ruined one of the plugs but we believed the coils were the cause of the misfire issue. 65k miles now.
wow - those plugs lived 2 or more lives !
Mine were done around 45k the first time and actually the coil ruined one of the plugs but we believed the coils were the cause of the misfire issue. 65k miles now.
 

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Are you sure those are the original plugs? Normal schedule is 50k miles. The electrodes don't look very worn. I would guess at those being the 2nd set, but I could be wrong. The plugs I took out of my S5 at 42k miles showed more electrode wear. :)

A dodgy plug can take out coil packs too by having increased resistance.
 

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Also worth checking for thermostat issues, my B8 S5 was losing power at high revs and the EPC light came on. Turned out to be a faulty thermostat. From what I gathered from the specialist, many things on these can play havoc with the control systems on the car. I'd echo what others are saying and go the logical route with coilpacks first though.
 
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