Recently I've started having worse gas mileage than I used to and the idle seems to be getting worse as well. I used to get about 420 or so miles every tank and now it ranges from 300 to 350. They both started happening around the same time so I believe they may be related. I have cleaned MAF, IACV, TB, EGR tube not too long ago. I removed the coils and one of them was kind of a brownish/orange color where the rest of the were just black. Then on a different cylinder one of the spark plugs was a lot more brownish color than the rest.

I had a fuel injector issue recently where the bottom o-ring fell off and was flooding the the cylinder but got that resolved but I'm wondering if something similar is happening now. CEL is not throwing any codes.

One more thing I noticed was when looking into the UIM through the throttle body it looks really wet inside and there were puddles in there. Not sure if it was coolant or fuel. I have noticed a gasoline smell inside the car a couple times but it would eventually go away and then don't smell it anymore. Don't really smell it under the hood either.

I guess my questions would be, is it supposed to be wet inside the UIM? Does a orangish/brown coil indicate anything? Does a brown spark plug indicating anything (they were all replaced recently with NGK)?

Any input is appreciated! Thanks

 

So your averaging 21 - 28 mpg. Not to bad. Was the whole coil a different color, indicating a non OEM part? If your net getting a check engine light for a misfire on that cylinder, leave it alone. The brownish color spark plug could be an indication of a rich condition, maybe you have another injector leaking?

 

Yeah it's not really that bad of gas mileage just that it was a steady 420 miles before the fuel light would come on and then all of a sudden getting rough idle and it dropped to 300 - 350 miles per tank so thought it might be relevant. They are all original coil packs. It wasn't the entire coil just kind of the middle seemed like a mix of black, brown, and orange where the rest of them were just complete black. Car currently has about 170,000 miles. I've read they are a common failure on 99' maximas.

Any idea about the inside of the UIM being soaked with puddles inside it? I'm thinking i'll remove the UIM as I think I hear a vacuum leak as well but can't pin point it. Tried spraying carb cleaner all over and can't find it but it sounds like it is coming from the TB area.

 

Not sure what would cause the discoloration on the coil...
Measure the coils resistance, make sure they're all within spec. Replace any that are questionable. Was the wet intake found after the engine was run at operating temps for a whole, or shorter runs not getting fully hot?

 

Ok I'll try to test the coils this weekend. Yeah the wet intake was after the engine had been running for awhile.

 

I had the same issue with my 97 maxima. Rough idle and the gasoline smell coming through the vents. When doing some investigating, I realized that my IAT sensor was bad and my gas mileage had went down significantly and the smell of gasoline was taking over my vehicle. I replaced it and the idle went back to normal and the gas smell was no longer there. FYI your IAT sensor is on the air intake system.