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I have a 99 suburban K2500 4x4 with the 7.4L. I have ran a couple of different code readers to try and find out what is causing my engine to run rough and all they are telling me is the engine is running rich. I have been told by a couple of mechanics that the intake gasket will start leaking and cause this problem so I changed it out and found that was part of the problem. The gasket had failed and was leaking coolant, but did not fix all of the problem. Does any body have any ideas what else could be causing this problem. I have a k&n air filter that I just cleaned out and the plugs I changed out about 20000 miles ago.
 

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What codes are you getting? Are there other symptoms (black exhaust, fouled plugs) that would confirm that the engine is running rich or does the engine actually appear to be running lean? If it's an O2 sensor code, is it on both sides or just one side?

"By the book" diagnosing a rich code usually starts by checking the fuel pressure/fuel system to see if that is a cause of too much fuel getting into the engine.
 

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The code that is coming up is P0172. When I first start the engine it puts out a lot of exhaust but it does not smell out of the ordinary and is white. After a few minutes after warming up it goes away but it runs ruff when idols. The last test I did just said it is rich on the left side. I will pull the plugs and check them for wear.
 

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Alright what plugs are you running in it? also When was the last time that you cleaned the maf since the oiled K&N filter can cause damage to the Mass Air Flow Sensor (MAF) and when that happens it will make the motor think it is getting more air than it really is.
Also check for vacuum leaks. there a few lines on them that can cause a leak big enough.
And take a look at this link it goes over everything that i just talked about.

http://www.obd-codes.com/p0172

---------- Post added at 12:29 PM ---------- Previous post was at 12:29 PM ----------

Also for cleaning the MAF be sure to use MAF cleaner not brake cleaner like mentioned since that will damage the MAF..
 
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