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I have emissions testing coming up for my '07 6S, but my CEL came on with a P0300 code with 182K miles. Replaced the pugs and coils last year. Car idles a little rougher than normal, efficiency is down and when accelerating, the engine sounds like I have an aftermarket exhaust on it, got a "lean code" the other week. I don't feel like dumping $1,000 into the car considering I will be getting rid of it in the next 6 months. My mechanic thinks I need a new Catalytic converter but I think the EGR may be clogged and hopefully I can clean it and fix the problem and pass the emissions test. Hoping that someone else experienced this issue and had it resolved. Thanks
 

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I have emissions testing coming up for my '07 6S, but my CEL came on with a P0300 code with 182K miles. Replaced the pugs and coils last year. Car idles a little rougher than normal, efficiency is down and when accelerating, the engine sounds like I have an aftermarket exhaust on it, got a "lean code" the other week. I don't feel like dumping $1,000 into the car considering I will be getting rid of it in the next 6 months. My mechanic thinks I need a new Catalytic converter but I think the EGR may be clogged and hopefully I can clean it and fix the problem and pass the emissions test. Hoping that someone else experienced this issue and had it resolved. Thanks
Hello. Plugged exhaust can cause a misfire. You may also have a vacuum leak (say accordion hose). Did you go with platinum plugs and decent quality coils?
Check the easy things first. Make sure all the coil plugs are firmly attached and no obvious hoses are disconnected (especially at the back of the intake or under the throttle body.
If all that checks out, your plugs look good and all the coils test properly I would check fuel injectors.
If you strongly suspect catalyst (a very reasonable assumption on a higher mileage v6) you could try to run the car without the upstream O2 sensor. Taking it out will allow some of the exhaust to bypass the converters and if you get better power then its likely a clogged exhaust.

Try taking out the crank and cam position sensors (very easy) and wipe the excess metal off them. Mine ran significantly smoother after (although it wasn't mis-firing before)
 

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Thank you, did a quick visual of hoses but plan on getting more in depth today. Coils and plugs look good. I used standard motorcraft when I replaced. I can a bottle of Cataclean yesterday just to see if it would do anything. Had better acceleration and no P0300 code when I floored accelerator and engine sounded better when accelerating. Refilled and P0300 code popped up again. Will try all of your recs today and try cleaning MAF sensor. Thanks!
 
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