2010 1.3 CZ2 Mitsubishi Colt

[Fishpie90]

Hello PH
Long time lurker here and I am hoping you could assist with an annoying but not detrimental problem I have with my Mitsubishi Colt, 1.3 manual, petrol, 63k
I picked up a cheap motor for winter driving and although there is nothing majorly wrong with the car, aside from being a bit agricultural, it does have an annoying issue.
After the engine is warm and between 1500-2000k rpm there is a random very short slowing. I am not sure how to describe it "an opposite of a surge". As if the break peddle has momentarily been pressed, it is not a judder just a noticeable slowing.
It only happens when maintaining speed, if I have the clutch in no issue. If I am in a high gear using engine breaking when descending down a hill no issue. If the revs are outside this range no issue.
No problems with accelerating or pulling away, starting, or rough idle.
I have had the car serviced, plugs, filters, fluids and this did not immediately resolve the issue, a few days after it randomly stopped for a couple of months until it came back.
This happened to be after the car wouldn't start and I used a battery pack (although the battery was not dead as it turned out). Although I am not sure if that was just a coincidence or not.
After some browsing on PH forums, I have replaced the ignition coils but sadly no effect. There is no noticeable back fire and the car starts on the button first time, each time apart from the aforementioned.
Any ideas?

Edited by Fishpie90 on Wednesday 12th February 11:46

[GreenV8S]

Could it be throttle position related rather than engine speed related? That car's old enough that it could have a worn throttle pot.

[Fishpie90]

GreenV8S said:

Could it be throttle position related rather than engine speed related? That car's old enough that it could have a worn throttle pot.

Could he a possibility, having done a bit of research I would have thought to have some other issues of it were that such as dodgy acceleration. I'll keep an eye on that though.

Could it be a clogged/bad fuel filter? If the issue goes away at higher revs could that be there's enough pressure / delivery of fuel to get passed a bad or clogged filter?

[E-bmw]

Fishpie90 said:

Could it be a clogged/bad fuel filter? If the issue goes away at higher revs could that be there's enough pressure / delivery of fuel to get passed a bad or clogged filter?

No, the fuel pressure comes from an electric pump that is on all the time & a pressure regulator regulates the pressure with reference to the intake manifold pressure.

As more fuel is used at higher revs it would get worse with revs if that were the case.

[stevieturbo]

GreenV8S said:

Could it be throttle position related rather than engine speed related? That car's old enough that it could have a worn throttle pot.

It's only 10 years old, almost no chance.

And that would yield fault codes.