Terrible Mileage - Spark Plugs???

Hello,

Recently, I had my 1990 Jetta Auto (Gas...1.8 I think?) in for a tune up, and I complained I was getting poor mileage (at that time, about 22mpg). After they did an entire tune, and replaced the spark plugs, I am now getting 18.6MPG!!!

Now, it seems that they replaced the plugs with some RENU brand (which I've never heard of) and I'm assuming they're nothing special.

Should this engine be using Platinum Plugs, and would that make all the difference? The plugs I was looking at getting right now are the Bosch Platinum 4's, but I want to know if this is actually going to significantly improve things.

Thanks,

Macdian

The RENU brand probably won't make a significant difference in MPG unless they weren't gapped properly (gap is .028 - .032" for non-platinum plugs). Your car didn't come with platinum plugs, but they are available and last much longer. I like the +2 design the best, +4 is a little overboard for your application. Did they check/replace any filters?