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Severe idle issues


ok, so im having an idle issue with my kia rio 03 160,000 miles with no check engine light. when it starts the car idles around 900 rpms and is very rough; after a few miles it will start to drop to 7 or 8 then finally to 600 at this time the car will occasionally die when idling to long such as at a stop light. it will start right up afterwards and i can generally save it if i see my rpm gauge start to flicker up and down il throw it in N and throttle the gas peddle until the light turns green. based on all the research iv done it can be a numerous amount of things so im hoping to narrow it down a bit. at this point it has new spark plugs (4 days old) and new distributor wires and a new distributor which i got from a local junk yard so idk if that is 100% working but its been working about a month or 2 now. in addition iv resealed the valve cover gasket the gasket itself seemed fine so i just resealed it although it didn’t work out perfect because cylinder 2 still gets a bit of oil in it everyday but i wipe it out regularly. im pretty certain its not the fuel pump because its been happening for about a month and hasn’t quit yet plus i can still traverse hills just fine. this weekend if nothing else i will be taking out my idle air control and giving it a good cleaning. and finally im not sure if these are related or not but on occasion il notice my temperature gauge will jump to 3/4 when it normally sits at half but it will return to half within a moment or so aswell as my transmission module is beginning to fail. thats pretty much it, keep in mind im not very car savvy mostly everything i know has been self taught through this car alone. if anyone has a recommendation of where to start that would be amazing, thank you for the read.

I hope that’s a typo…
I hope it is supposed to refer to 900 rpm, 700-800 rpm, and 600 rpm. :wink:

Either that or I need to get out more or buy a faster car or both.

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lol my mistake that wasn’t a typo, i thought it was thousands not hundreds. i did second guess myself when i typed it but i convinced myself otherwise

also assuming that is 160,000 miles ?? or is it 16,000 ?

Yes 160,000

This car could benefit from a senior car wellness check-up. It’s an 03 (75 in car-years). You didn’t happen to check compression while the plugs were out, did you? A compression test (wet/dry) would be a starting point.

Does this vehicle use any appreciable amount of vital engine fluids, such as oil or coolant?

Not sure what a compression test is but no i didnt. But i will look into it and see if it is something i can do with my limited expierence and tools. And as far as fluids it seems to be fine im not sure if there extensive testing for that but my levels are always good. However the problem did start right after i recieve an oil change at a local shop.

Any new mysterious whistle sounds?

No not that i have noticed it sounds fairly normal but its much louder then it used to be and the sound of the engine will go utoand down in pitch constantly but no whistle

Your reports of a change in the manner the coolant temperature is jumping up at times is concerning. That could indicate a head gasket problem, which could also cause poor engine performance especially at lower rpms b/c

  • coolant is leaking into the cylinders and causing misfires
  • compression is no good, causing misfires
  • outside air is being drawn into the cylinders, cause lean mixture misfires
  • oil leaking into the cylinders, fouling plugs

Suggest to start by looking at the coolant in the radiator. Do you see any oily residue, esp under the radiator cap? Anything at all unusual about the coolant? Is the engine losing coolant at all? Check the oil on the dipstick too. Notice anything unusual? Is the oil level on the dipstick rising over time for no reason?

If nothing found there, you’d need a shop to look for further evidence of head gasket problems. But it might have nothing to do with that. So read on.

The most common reason for poor idling is that unmetered air is leaking into the engine, bypassing the MAF. This causes too lean of a mixture in the cylinders, and resulting misfiring. It’s worse at idle b/c there’s very little gasoline being injected at idle. The extra air swamps the gasoline out. As the rpms increase more gas is injected and that extra gas will mask a small air leak. One place air leaks happen is the brake booster. It’s connected by a thick hose directly to the intake manifold. So ask your shop to test the brake booster and its hose for vacuum leaks. There’s other things that will cause this, but some of the above are ideas anyway. You’ll likely need to bring a shop in for a proper diagnoses.

well a shop would be my last ditch effort which might not even happen there is alot of problems with this car and im just trying to get by until October. new info though i filled my gas tank to half and it almost immediately died at the next idle which was a drive through it was at 600 so i had my hand ready just in case and it just dropped to like 200 and began to sputter heavily it was definitely faster then all the other times. so maybe i should reopen the fuel pump case. however it does sound like that might further more support your statement of unmetered air. is that something ? and i will check my radiator cap in the morning and go from there.

If the two are related, could be a faulty purge valve. When you fill the gas tank the fumes displaced are supposed to go into the canister, and only when driving at a healthy speed, the purge valve opens and routes the stored fumes from the cannister to the engine. If the purge valve is open all the time, this symptom can result. A faulty canister can cause it too.

A faulty fuel pump check valve wouldn’t be a likely cause for the above symptom, if that’s what you mean. A leaking fuel injector could though.

Other ideas: Problematic idle air control devices, electronic throttle bodies, and sticking throttle valves are often involved in idle rpm wandering. I had that problem on my Corolla and it turned out to be the idle air control gadget.

If I had those problems on my Corolla the first place I’d start is a complete vacuum system check. Followed by a fuel pressure test. Then a throttle body service. Somewhere along that route I expect the problem would be discovered.

ok so today i tried to locate and clean the iac but i couldn’t find it. i found the throttle body it was a little greasy but not to bad but i couldn’t get below it because i dont want to go to deep and not be able to reassemble it. i was told that if i take off my air filter box i would easily be able to see it but i looked with no luck. is it possible its on the bottom or does my model have a different looking one then im used to, based on picture iv seen for this model they all look the same. also i checked for anything unusual with my coolant and oil everything seems to be fine.

It sounds like you need some assistance beyond what can be provided over the internet. Suggest to either secure a repair manual for your make/model/year, or hire a mechanic to help you at least get started.