RPM drops and car shuts down when I change gear

ABDELLATIF ABDOU

MEMBER
2006 MITSUBISHI LANCER
1.3L
3 CYL
MANUAL
165,000 MILES

Hello, and thank you for reading this.

This morning when I came to start my car (CS1A I think ), the crank was so low and the car could not start. I figured it was the battery, so I used my neighbor's battery to start the car, then I put mine after ( while engine is running ). I went to a battery dealer who tested the voltage and told me the battery was bad, but the real problem is, even if I am now starting my car normally, when I change gears the rpm drops to 1000, and when I shift back the rpm drops to 300 to 400. The battery light goes on, and if I shift back to first gear it also makes the car shut down and I have to start it again.
After seeing an auto-electrician he said the battery was faulty, and my mistake was replacing the battery while engine running, but the car should re-program itself shortly in a day or two (he meant the ECU I think ).
My question(s) is : Is that true? If yes what should I do in situation overall?
If not, how much damage have I done in this case please?
Please note that there is no Mitsubishi service where I live, and any repair would be done at local garage.
I would infinitely be thankful for any advice or piece of information, and sorry for the trouble.

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5 Replies

CARADIODOC

MECHANIC
33,873 POSTS

You were told correctly about removing a battery cable while the engine is running. That can lead to voltage spikes and numerous damaged computers.

Your car is newer than most that develop this problem, but the solution might be the same. Also, this applies to Chrysler products, but Chrysler uses a lot of Mitsubishi parts, and they do a lot of things the same way. Your mechanic was right about the engine computer relearning data while you are driving, except for "minimum throttle". Until that is relearned, idle speed will be too low, often to the point the engine will not start unless you hold the accelerator pedal down 1/4". This is the one thing that requires specific conditions for the relearn to take place. To do that, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.

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Thursday, January 11th, 2018 AT 7:06 PM

ABDELLATIF ABDOU

MEMBER
3 POSTS

First of all thank you for your prompt and very helpful reply. Yesterday I noticed that after driving for a couple of hours, the car started going back to normal (well no shut downs at first gear), then I went and got myself a new battery, when I replaced it same thing happened again, until I drove it back home and parked it. The following morning she was working fine again. I will take it tomorrow and do exactly what you said, maybe it will explain the loss of power I felt lately.
Anyway, I cannot thank you enough for your help, I hope we can benefit from your advice, for as long as there are cars.

PS: should I shift to neutral or just drive to fifth gear and cruise?

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Friday, January 12th, 2018 AT 12:01 PM

CARADIODOC

MECHANIC
33,873 POSTS

This will not work in neutral. The engine computer needs to know when you have your foot off the accelerator pedal, then it takes a reading from the throttle position sensor and puts that in memory. From then on, any time it sees that same voltage, it knows it has to be in control of idle speed. The condition that triggers it to do the relearn is high manifold vacuum for seven seconds. You can get high vacuum from just snapping the throttle, but not for seven seconds. Vacuum will not be high when the engine is idling. That is why you need it in gear when coasting.

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+1

Friday, January 12th, 2018 AT 7:47 PM

ABDELLATIF ABDOU

MEMBER
3 POSTS

Thank you ''Doc'', so I did exactly as you said, drove it for about ten seconds without touching any pedals, the idle is now stable as far as I can tell, the car is running just fine thanks to your advice. Although I still have this feeling that the acceleration is not as it should be, especially when driving up a hill, but it is just me I suppose.
Anyway much appreciated help, really detailed in depth and informative responses, and I want to give you a hug lol.

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Saturday, January 13th, 2018 AT 4:17 AM

CARADIODOC