Rep Power: 0

I just got my oil changed at the dealer and was told that I'm due for plugs and valve adjustment. (MM 15)Car runs great is this really necessary at it is $400.

 
Rep Power: 142

Plug replacement is suggested at 105,000 miles or when it is coded for it in the maintenance minder. Valve adjustment is generally suggested if the engine has more tapping than normal. It may be legit or it might be someone trying to make money off of your car.

How many miles does the car have? I assume it is the 1.8l in a 2006-2011 civic from where you posted this.

 
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Sorry about that. It's a 2011 lx. 105,000 miles. I understand the adjustment more than the plugs. If they are clean and engine runs fine. Gas mileage is about 350 tank. Lots of city driving.

 
Rep Power: 142

I will say that I have been at a honda dealer for 9.5 out of the last 13 years. The other 3 years was with toyota. In that entire time I have seen 1 actual bad denso platinum/iridium spark plug and I have never seen a bad NGK platinum/iridium spark plug.

The only platinum/iridium plugs I have even seen NEEDING replaced were damaged by some other factor such as a bad ignition coil or oil consumption.

 
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Ok just spoke to my local mechanic (who gets great reviews). Said it about $130 plus gasket. Plugs should be fine. But they will check them.

 
Rep Power: 308

They are at rated life or very near. (Get OEM plugs)

My mechanic said the R18 valve adjustments are rare.....run until noise occurs.

 
Rep Power: 229

$130 seems about right. But I'd leave them like others have said unless there is major valve chatter.
It's probably a 45min job if you know what your doing inside and out.

Book time will bill it at 1 hour which would be the average time it took a well trained mechanic who may not know every bolt or the sneaky tricks a honda tech would know.

I think it took me maybe an hour, all in all, when I adjusted mine and that was the first time I pulled the valve cover.