Dear Tom and Ray:
I have about 140,000 miles on my car, a 2006 Toyota Prius that misfires at idle when cold, and for the last 10,000 miles the engine has been using between 1 and 2 quarts of castrol synthetic 5w30 oil between the 5,000 mile oil changes. My check engine light naturally stays on constantly now and the engine also appears to misfire on acceleration also.
For the first 60,000 miles I had the oil changed at various places every 3,000 miles using nonsynthetic oil that was recommended in the car manual. Since then I have been getting the oil changed at the dealer where I bought it new and they switched to the synthetic oil, so I asked the service department, why the misfire?
They said the new type spark plugs are very sensitive to oil burned in the firing chamber, causing the misfire. They told me to check the oil often which I do and the engine has never been more than a quart low.
Is there a spark plug I can use that is not as sensitive to the oil, or should I be looking for a junk yard engine or is it cheaper to have my engine taken apart and repaired. Will it damage the engine further to keep running it, there does not appear to be any smoke coming from the tailpipe.
From new I got mpg in the 40’s now I am getting 33 to 34 mpg.