Erratic RPMs at idle/start-up | Solved with fuel system cleaner

[Fummins]

Dirty maf? Ever change the plugs?

[Fummins]

The engine still surges upon warm-up, but the vehicle otherwise has no problems. Now at 133,000 miles.

It surges during warm-up then idles fine once warm? Has your battery/alternator been tested? The electrical systems in these cars are super sensitive and small changes can make the car do weird things.

[dspace9]

I have a 2015 Mitsubishi Mirage ES with a CVT, 128,412 miles.

That's a lot of miles on your original battery.

[Eggman]

I really hope it’s not the fuel pump. I found some cheap gasoline additives at Dollar Tree, but it hasn’t done anything

Try Techron, a fuel system cleaner, rather than a gasoline additive.

[grevster]

Five minutes is plenty of time to check for vacuum leaks on a cold engine. When I check for leaks I start the engine cold and spray carburetor in areas where I suspect a possible leak. If the engine idles higher when I spray a certain spot then I’ve found the source of the leak. It’s not rocket science and only takes a few minutes to perform this test.

I don’t think it’s a vacuum leak though. It sounds more fuel related to me. I would do two Techron treatments (one after the other) and see if it fixes the problem. If it fixes the problem, switch to a top tier brand of gasoline and do a Techron treatment from time to time. I do a Techron treatment every time my tires are rotated and I try to only use top tier brands of fuel such as Shell and Exon.

Do you suggest driving continuously a long distance with the treated gas? I am mostly using the car for a 20 minute commute x2 everyday and I am not sure if it will be enough to get up to a decent duration to run long enough at high enough temperatures.

I have problems finding Techron in Calgary, Walmart Canada has it as pack of 6 and it costs $145 https://www.walmart.ca/en/ip/Chevron...RD57QK5MGEUVZ5. I just need two bottles of this. I already had a bottle of gumout, I will give it a try to it first then will try to find a Techron.

[dspace9]

Do you suggest driving continuously a long distance with the treated gas? I am mostly using the car for a 20 minute commute x2 everyday and I am not sure if it will be enough to get up to a decent duration to run long enough at high enough temperatures.

I have problems finding Techron in Calgary, Walmart Canada has it as pack of 6 and it costs $145 https://www.walmart.ca/en/ip/Chevron...RD57QK5MGEUVZ5. I just need two bottles of this. I already had a bottle of gumout, I will give it a try to it first then will try to find a Techron.

You know there greyvster, before you pour anything into your Mirage, get a basic tune up done. Things like spark plugs etc. oil filter. oil. new battery tune up items. Not much else to the Mirage.

My word I wouldn't be doing anything to my Mirage besides a proper tune up. Myself, I need new drum brakes on my '14 Mirage with 121,000km's on the od.

I broke my old Ford Escort using additive I picked up on the fly from a Walmart in northern Michigan. So I would be wary. Not fun being stranded in a foreign land lol. I made it a great time of course, pawning Canadian beer for rides around the UP. Get the basics done and see how your Mirage is. Annoying but it costs money to have preventative or even just smooth running transportation. Nothing stays new forever.

[Mark]

I really hope itÂ’s not the fuel pump. I found some cheap gasoline additives at Dollar Tree, but it hasnÂ’t done anything

I looked up Steve's discussion on this topic, because he bought a new fuel pump & clutch kit. A bottle of Techron, however, solved his problem. This issue popped up for him @ 206,000 miles. 60,000+ miles later those items he purchased are still sitting in the box. If you have dirty fuel injectors, replacing a fuel pump or clutch isn't going to fix that.

I am not a big fan of gas additives. If I had an issue, however, I would give Techron a try. I would add the recommended amount just before taking a longer trip with my car. If your goal is to clean your fuel injectors, it's going to do more good while the car is running (verses sitting the gas tank). I would also buy the Techron product that is meant to clean injectors verses the one that claims to treat your fuel system.

Steve's post -
206k miles - For the last few months I have been convinced my clutch was starting to go out. Every few days I would feel a loss of power while accelerating. Last week I noticed the rpm drop while idling, which is not indicative of a bad clutch. Loss of power, while not driving is either an ignition problem or fuel issue. I replaced spark plugs at 200k miles, so I wasn't too worried about ignition. I went ahead an ordered a used fuel pump on eBay for $40. While waiting for the fuel pump to arrive, I started thinking, maybe I just had a dirty fuel system. Stuff like a dirty fuel filter or injectors could cause a loss of power. Last week I switch from Racetrack/Walmart gas to Shell since it has extra detergents. I also did a treatment of Techron. Almost instantly my problem was gone. I'm planning to keep running Shell gas and to do another treatment of Techron on Monday. I will keep this thread updated as time goes on.

I do think other suggestions have been good. If you are over 100,000 miles, changing spark plugs is just part of normal maintenance. Normal maintenance items like oil/filter, air filter, etc... should not be neglected. Most places like AutoZone will test your battery and alternator for free. If it's time for a new battery, by all means do that. It may not solve your problem, however.

I wouldn't use a dealership to do simple maintenance items, but that's me. Warranty or recall items are the only time a dealer is going to see my Mirage. If I didn't feel like changing plugs, I would have my local mechanic do it for way less money. If you are up to date on your normal maintenance items & quality fuel injector cleaner doesn't help, I would have items like your MAF sensor, fuel pump, gas filter, etc... checked out.

Given what Steve has shared, I would try a bottle of Techron first. It's cheap and easy to do.

[grevster]

Here is an update, I used a bottle of Gumout all in one cleaner in a full tank of 87 octane gasoline (sorry, i could not find any techron locally) and drove 2 hours continously on the highway around 110 - 120km/h. The next morning, when i started from cold, i still had the erratic idle but this time it was not bouncing between 1100 rpm - 750 rpm but it was bouncing around 900 - 750 rpm. So the amplitude of idling bounce reduced.

I gave another bottle of Gumout this time in half tank Shell 91 octane gasoline. It is still in the tank not finished yet but when i checked this morning, i didn't see any bouncing at all. Of course i need to check couple more morning cold starts to make sure but i guess it is getting much better and cleaner really helped. Thank you all!

[stevedmc]

Awesome. Techron is based on PEA and I believe Gumout is as well. Just keep doing treatments until your car idles perfect and add it to your regular maintenance schedule. It won’t hurt to only use Top Tier fuel from now on as well.

[Eggman]

Here is an update, I used a bottle of Gumout all in one cleaner in a full tank of 87 octane gasoline (sorry, i could not find any techron locally) and drove 2 hours continously on the highway around 110 - 120km/h. The next morning, when i started from cold, i still had the erratic idle but this time it was not bouncing between 1100 rpm - 750 rpm but it was bouncing around 900 - 750 rpm. So the amplitude of idling bounce reduced.

I gave another bottle of Gumout this time in half tank Shell 91 octane gasoline. It is still in the tank not finished yet but when i checked this morning, i didn't see any bouncing at all. Of course i need to check couple more morning cold starts to make sure but i guess it is getting much better and cleaner really helped. Thank you all!

That's good news. Please check back in a couple of days with an update. I'd like to include the solution in the first post.