Hi, i changed the spark plugs and motor oil 3 years ago. So, the new sp are NGK Iridium.

i have noticed a 20 or 30% less miles per gallon. The car is running ok, but i feel that the idle rpm is a litle high.

After i took the car from garage, it has the Service light on (they confuse 2 wires ). i did the manual procedure for reset the ecu and the light disapear.

Do i have to reset another thing?, maybe the maf sensor or something?

thanks in advance

LG

 

You left out a lot of information:
1. Have you changed the oil since then or are you still running 3 year old oil? Not trying to be a douche, just wondering why you included that info.
2. What brand and model plugs did you use?
3. What gap did you set the plugs at?
4. What is your idle rpm with and without the A/C on?
5. Are you sure you have the wires connected properly and fully seated? 20-30% mpg loss sounds suspiciously close to what I'd suspect you'd get running on 5 cylinders...
6. Did you notice a loss in power after the plug change?

You may also be able to run a conductivity test on the wires to make sure they weren't damaged...may be more worthwhile to just replace them along with a new set of properly gapped plugs and see if that fixes your issue.

 

sorry, 3 days ago.

 

LOL, I was gonna say...maybe you should think about changing your oil again.

 

Could it be that more gas is now partially mixed with ethanol?

 

if you had a code,you need to retrieve it as your starting point.otherwise your needlessly hunting in the dark.