Strange revving at idle today

[Mirageman38]

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[dspace9]

Could be a fluke... one time thing.

[Eggman]

What kind of gasoline do you use in your Mirage?

[TJ18CVT]

Maybe the MAF sensor needs a quick cleaning..this is my first rodeo with a Mitsu, but I've had GM's that did this.....

[dspace9]

This is only about 8 months old and only 16k miles. The gas was Wawa 87 octane.

Your engine is just being broken in at this point then. I don't think any piece of technology runs exactly perfect all of the time. The demo I test drove at the dealer years ago was a rickety thing under the hood.

Another thing is maybe some of the threads on here are making you uneasy about things, so you're listening hyperaware for problems that aren't there. Like how Dirk is always worried about his CVT.

Might be nothing eh!

[Eggman]

This is only about 8 months old and only 16k miles. The gas was Wawa 87 octane.

I don't doubt the symptoms you are reporting. The thing is, it could be several different reasons why. The most likely possibility that I can imagine from here would be funky fuel. I'm not familiar with Wawa fuel so I looked it up. It is not listed as a Top Tier licensed brand. Not sure if you have followed the threads here on this, but cheap gas has a track record of causing problems.

Try running some fuel system cleaner (not fuel treatment) such as Techron, follow its instructions and see if that improves things. It's cheap and easy.


More reading on the subject of Top Tier fuels:

The Truth About Cars: AAA Study Finds Drastic Differences In Gasoline Quality

According to the AAA study, the non-Top Tier fuel caused carbon deposits that were 19 times higher than the deposits from the Top Tier fuel. They also saw better drivability and better fuel economy when the better fuel was used. Emissions were also reduced, likely due to the ban of metallic additives in Top Tier fuel.

The laboratory completed the test on a Ford port injected 2.3-liter engine, which appears to be the Lima engine from the late 1980s. This engine has been used for testing for about 15 years and is a popular one, due to the orientation of the valves (which shows the difference in carbon deposits in just 100 hours of testing). The full report shows compares the average 34.1 milligram carbon deposit in the Top Tier fuel test to the average 660.6 mg carbon deposit in the non-Top Tier fuel test.

Pictures illustrating the carbon buildup of lower-quality fuel can be found at the link.

This TTAC news article is based on a AAA report on Top Tier fuels.


The takeaway is cheap gas isn't the bargain it appears to be if it causes engine fouling.

And please let us know how this goes. It's always helpful to let us know the solution so it can be shared with others.

[Eggman]

Hey Mirageman38, what other details can you give? Like how much RPM variation are you noticing? I wonder if this is something like an A/C compressor cycling, or your alternator loading down the engine. Fummins (?) reported some bad alternator wiring and I can see an intermittent alternator field controller wire causing these symptoms. Are you able to monitor vehicle voltage somehow? Just brainstorming.