Intermittent high / fast idle?

iacv is the likely fault, under larger throttle openings they open, when throttle is released they should close, but if they are dirty then they can stick open or close very slowly. The long term cure is to run on good petrol and oil (and change it regularly) To prove it is the iacv just disconnect it and take it for a drive, you may well have warning lights and it may not idle, but if the 3 - 4 k revving is gone then it is very likely the iacv , next would be remove and clean it or replace it, depending on ease of access and cost.

Thanks for that.

I've sorted issues before with IACVs on other cars - and actually found tha= t once either cleaned up, or replaced, I didn't have a repeat of the proble= ms, I tend to drive 50 or 60 miles at a time, so always used to find that o= nce cleaned or replaced they largely stayed clean (same with the throttle b= ody).

I did find on one Volvo (S70) that when the IACV was playing up, and / or u= nplugged, warm / hot idle was high.

I'll try and give it all a good clean today. I'll also try and unplug the I= ACV if I can get it to idle hot again, and see if that shows a difference.

Thanks again.

Likely a problem with the ICV. (Idle control valve). They are commonly a stepper motor moving a valve, controlled by the ECU. Removing and cleaning can often work.

Update: got chance to have a tinker under the bonnet at lunchtime.

I was wrong about the type of throttle - it isn't electronically actuated, = it does have a cable, it just wasn't that obvious from my first looks. I re= moved the induction trunking to the throttle body - have to say, the thrott= le body and plate looked quite clean.

The IACV was where I thought it was, bolted to the rear / firewall side of = the throttle body. I removed it and gave it a good clean with carb cleaner.= Looked a bit black inside, but not as filthy as I imagined it to be. Took = a bit of cleaning with some cotton buds, to get the metal flap and other ar= eas as clean as I'd like. As with other IACVs, when I'd finished cleaning i= t, I could feel the flap move a bit inside, when I swung the IACV - so seem= s to be moving freely as it should.

Put it all back together and ran the car up to temperature (parked up, mind= , not driving) and the idle speed behaved perfectly, but then I'm not so su= re it wouldn't have done the same prior to cleaning it. Even when warm, bli= pping the throttle had no lag or hesitation about the idle returning to whe= re it should be.

Road testing and general driving should give more of a clue as to whether t= hat's done the trick.

If it still plays up, I'll unplug it, see what difference that makes.

Thanks for the help, chaps.

it would behave while stationary as the opening is only done in response to throttle opening combined with road speed.

Further update: did journey of about 5 miles to nipper's nursery again, when I got there, engine was warm, idle about 2k revs. With the engine on, unplugged the IACV. Revs dropped a fair amount (at a guess to about 1200-1300rpm - experience with iffy IACVs in the past tells me that tends to be where the engine idles at, when warm, and IACV is either broken or unplugged).

After that, switched off, took ankle biter in to nursery, then drove another couple of miles, filled up with petrol. After that (ie turning on after filling up) then check engine light came on - I'm guessing that's almost certainly due to unplugging the IACV, and idle trim being out of bounds? I'm ever hopeful, that the Kia's engine software is one of those that doesn't need the light turning off with a specific tool / gadget (some cars, seem to right themselves where check engine lights are concerned, when it's been fixed, and several ignition cycles have been done, others, though, seem to require a software device to reset it).

Drove about 60 miles, then, car behaved as expected, warm idle

1200-1300rpm (as I'd expect with the IACV unplugged) but no issues when blipping the throttle, idle returns to it's previous point.

During the day, I've left the plug connected - to avoid any moisture ingress into the connections. I suspect if unplugged when started from cold, idle will be a bit too low (from what I've experienced in the past, 400-600rpms with a broken / disconnected IACV).

So I'm going to source a replacement, should be able to muddle through with it until then. Conveniently, you can read the part number on the IACV with it all connected up. What I'm wondering is, whether the crafty Kia people did that simple out of cleverness, pure dumb luck, or because the IACVs they use have a propensity for failure.

Thanks for the advice, chaps, will probably update the thread once I've put on a new IACV, just to confirm / deny it's properly cured the issue.

Generally, they are not the most reliable of devices. The ones used on the Range Rover with the old Rover V8 are a constant source of problems.

3rd update!

Not meaning to mither, but it may be of some use to somebody else...

I drove around for a couple of journeys with the IACV unplugged (although plugged it in when stopped, to try and avoid any moisture ingress). Truth be told, it didn't seem a world away from where it should be - most noticably, the idle speed was consistent, but higher than it should be (at a guess around the 1200rpm mark). That was the same whether the engine was warm or cold (I started it up, after being left around 8 hours, parked up) and the cold idle was at this point (but remained at that point). No issue with blipping the throttle leaving the revs high, though. As I mentioned in my previous post, after about 3 cycles of the ignition, with it unplugged, the check engine light came on.

I bought an aftermarket IACV (was just shy of =A350 - Kia dealers wanted around =A3150, and other sites selling OEM spec ones seemed to be in that order).

Looking at it, and inside at the workings (from what you can see down the tubes) it looks identical to the OEM one I took off. Design looks identical, markings look identical, I supposed the gubbins inside might be of inferior quality, but doesn't look to be from the outside.

Anyway, I've put this new one on the car, and it behaves perfectly as it should do - but only tested with the car stationary. After 3 cycles of ignition, the check-engine light went out - so yay on that score.

I'll probably post one more update as to whether it's truly fixed the problem when I've had chance to drive it properly, and get the engine fully warm.

Thankyou.

4th update!

Not quite as positive as I'd hoped. For 3 or 4 days I thought I'd got it sorted - with a replacement IACV (new, but pattern part). Over mainly distance journeys (around 60 miles at a time) and some shorter journeys, it behaved perfectly with the new IACV, when it would have definitely showed behaviour as before replacing the IACV.

But today was a different story - quite a warm day, just short journeys, with the kids, mile or two at a time, often with the air-con on a lot. It happened again - revs creeping up to around 2k when idling and stationary - and it sort of creeps up there, too. Any blip on the throttle would make the idle rise to, say, 3k revs and stay there.

One other thing I noticed, when it's doing this - say stopped at traffic lights or at a junction, when it's idling high like this, switching on the air-con brings the idle down to about 1k revs - which seems a lot of change, accepting that an air-con compressor is a far amount of drag on the engine.

One other factor - one of the drive / auxiliary belts must slip at times - most noticable at low engine speeds, with the air-con on. I've not noticed the battery / alternator light flickering when it's doing it, though. I'll have to get that sorted, it's nagging at me that it's in some way related.

So I'm left with the following possibilities:-

1. Original IACV was bad, new one has gone bad in a short number of days - a possibility. I'm pretty sure that when it's revving high, if I unplug the IACV, the creep / rise in idle revs to 2k, won't happen, so it's clearly related.
2. Some condition of the engine, is making the IACVs go bad. Everything seems OK, otherwise, no oil consumption, fuel consumption seems about right. When I'd looked at the throttle plate / body, it was cleaner that I'd expected - truth be told, the trunking to the throttle body, and the clip and bolt looked like they'd never been apart or unfastened - so I expect nobody had ever had it apart before I did.
3. Some condition, fault, or problem is making the ECU tell the IACV to behave this way. Seems odd, and unlikely, but if it's the IACV that's making the engine race when it should be idling (and unplugging it when it's doing this, and seeing the revs drop to where I'd expect, were the IACV not operating implies that), and there's a certain degree of unlikelihood that a new replacement IACV is either broken in less than a week, or made bad by some condition of the engine - then I have to at least accept the possibility.
4. Some other fault / problem / issue is causing this behaviour, and unplugging the IACV when it's doing it, stops it, but masks the true cause - dunno how plausible that is.

There's no check engine light on, or any other warning lights on - and they all seem to work correctly - come on when the ignition is turned on, go off when the engine is started. Nor is there any behaviour or condition of the engine I can look at that seems overtly wrong - with the exception that I can hear one of the belts slipping at times, at low engine speeds, especially with the air-con on.

I think the next course of action will have to be unplugging the IACV for the moment - it's more tolerable to have a permanently slightly higher idle, than one that is far too high when the engine is hot. This will no doubt, put the check engine light on, like last time, which went away, after installing the new IACV, plugging it in, and 3 cycles of the ignition / engine start.

After that, I think I should probably buy one of those cheap code readers / erasers, plug in the IACV, clear any codes, drive it, see what happens, hopefully it will do it again, and read the codes.

In the meantime, any thoughts, ideas or suggestions welcome!

And I was so sure it was fixed, too.

Small airleak somewhere?

I wondered about an air leak, but thought if that were the case I could expect the problem permanently, even when cold?

There are times when it takes provocation to do it. Yesterday, I ran with the IACV unplugged - thinking it was the problem again, and found with it unplugged the first time, the car was much less problematic. What I found, though, made me reconsider the IACV as being the fault, and merely contributing to it when it happens.

I had two journeys of around 60 miles to do (home -> office -> home) - mostly motorways, and a couple of small journeys at both home ends. I noticed, part way through the morning motorway run, that the idle was higher than I would have expected (this is all with the IACV unplugged) - blipping the throttle doesn't seem to affect it with the IACV unplugged - but again, turning on the air-con, drags the idle speed down to about 1k revs.

So I'm guessing the hot idle rising is independent of the IACV, and perhaps with the IACV connected, the only issue being that throttle blips when idling, can push the idle up further.

Anyway, when I'd driven back to my home town, and had to collect my son on the way back home (by this point, I'd have driven a little over 60 miles), the car was idling around 1700-2000rpms, IACV was unplugged, I parked up, nipped in to my parents to collect my son - would have been in their house

2-3 minutes, no more than 5, so the car would have still been warm. Got in, started, car idled about 1k revs (IACV still unplugged - I suspect had it been plugged in at that point, idle would have been at the normal 800-900rpms). I then drove a short distance to my house, parked, left the engine running, and opened the bonnet - it would have been idling about 1700-2000rpms at that point. I tried unplugging the MAF (wondering whether that's what was causing this - and I'd read that often, unplugging it when engines are playing up, and it having no effect, is kind of suggesting it's knackered) - that seemed to make the revs rise ever-so-slightly.

So I then plugged in the IACV, and the revs dropped to a completely normal level (I suspect around 800-900).

Before doing that, I was inclined to think maybe cleaning the MAF (it's a Bosch MAF, from memory, similar is used on several cars / engines - in the trunking betwixt airbox and throttle body) - I'd read that being very gentle, and spraying on a little carb cleaner and letting it evaporate off, can often clean the thin wire.

Now, though, and I think I'm going to be more cautious and not throw parts at it. I've ordered a cheapo, generic code reader, I plan on resetting / clearing all codes, and / or leaving the battery disconnected for a bit, connecting it up, plugging in the IACV, then driving it as normal, and waiting for it to play up, then seeing what the code reader says.

I'm partly wondering whether there's some odd adaptation going on, here, and being confused at times with the IACV being unplugged (definitely brings on the check-engine light). But still, there could well be some real problem, here, and I'm just a bit puzzled with it.

Any of what I've written sound daft, or is there any other approach anybody would recommend (and yes, I have considered just taking it to a dealers / garage to sort out, but experience has shown me - especially with main dealers - that with problems that are either intermittent, or dependent on temperature, they can be quite ineffectual, time-consuming, and inconvenient - in terms of having to get the car there, and often not having a courtesy car to give you - albeit at short notice)?

And sorry to mither and go on about it, but I'd love to be able to have sorted - or at least diagnosed this.

It'll still be there but the IACV will br almost closed instead of open when the engine's cold.

Would you expect a check engine light, at some point, though, with an air leak? 'cos surely if it's unmetered enough to disrupt warm idling, it's enough (over time) to trigger some condition. That said, reading the codes may be much more revealling.

The only thing that seems to bring on the check engine light at present, is leaving the IACV unplugged for 3 cycles of the ignition / engine start. Reconnecting it, and 3 cycles later, it goes out.

What's swaying me away from induction air leak, being that it only seems to be certain conditions triggering this. Today I just drove a shortish journey - and I've kept the IACV plugged in, now - the car temperature gauge got fully into the normal bit, and the IACV responded to bring the idle down from cold (little over 1k revs) to normal warm idle (800-900) and I drove for a few miles, locally, and had no issues.

I would have thought an induction leak would have meant it would behave the same any time the temperature got to the point where the IACV is bringing the idle down to warm / hot engine speeds - but that's not necessarily happening - and as I mentioned from my use, yesterday, after an hour, or so, driving, stopped for a couple of minutes, when I started again it idled perfectly 'til I'd been driving for a minute or so.

I guess if nothing else, one thing I've found is initially thinking it was the IACV, it seems to behave like this with it disconnected. Roll on the fault code reader arriving.

And thanks for your suggestions - anything making me think over it is help, and I'd really love to crack this nut.

Me too!, my olde Audisaursus has an almost identical fault thats more annoying that anything else. Its doing almost the same thing odd in that when its in fault mode the revs will go from 850 odd to 1500 as if your blipping the throttle. If you should rapidly switch the ignition on and off it more often than not settles down to 820 rpm till you put your foot on the go pedal when its off again.

IACV changed original was duff so I reckon theres another part faulty somewhere MAF seems clean must get around to checking some resistance readings. It is much worse when hot, both temp sensors changed, almost behaves itself when cold from start..

Have to say, I'm wondering about coolant temperature sensor. But then I don't want to blindly go buying parts - but it does seem at least as if it may be relevant. I just would have thought I'd get an engine light. I think the fault code reader, when it arrived, may shine more light on it.

Oddly enough, in other cars I've had, I've had check engine lights come on - or at least definite symptoms - for bad sensors - but in those cars, no warning lights from either bad, or disconnected IACVs.

Like yours, mine is fine from cold, and often (for short periods) fine when warm or hot. But when it starts happening, it doesn't yo-yo, if you slow down to stop, the revs may naturally fall to somewhere, say 1300-1500 revs, before declutching. Then when stopped, either in neutral, or in gear, waiting to move, with the clutch down, the revs stay at that point, and progressively rise to settle at around 2k. Air-con compressor being turned on, drags it down to around 1k, if I turned it off, the revs would rise to about 2k again. With the IACV connected, blipping the throttle would see the revs stick at their highest point. Blipping the throttle with the IACV unplugged, has the revs rise a bit, then drop down to about 2k.

And also like you, turning off the car, then restarting it can often see it behave normally - at least until driving around a bit.

Thanks for replying, the info is all sinking in.

Just one other thing (said in a Columbo manner...) - I've read a couple of comments, now, from web links suggesting an alternator issue for these symptoms. One was unqualified, the other in relation to a 2005 Mini, and said that the ECU had detected low voltage from the alternator, and decided to up the revs.

Does that sound tenable?

I mentioned, previously, that occasionally I can hear one of the drive belts slipping (tends to only really be noticable when the air-con is turned on), so I suppose that could be contributory.

If it was the alternator, should I expect to see any flickering or blinking of the battery warning light? Or failing that, would a fault code likely be logged?

Also worth noting, once when this problem occurred, I'd just left on motorway, and was waiting at a junction on a roundabout to join another. This would probably be when I'd first really noticed it. So I was stationary, the car was revving away at about 2k revs, I'd blipped the throttle and the revs had risen to 3k. Not wanting to sit there for a while, waiting for the lights, with the engine blazing away at 3k, I turned off - that may not have been the best thing to do, but it didn't seem good to sit there with it running at 3k revs, either. Then I struggled to start it again. But it didn't turn over and fail to fire, it just didn't turn over. I was stuck for a couple of minutes like that, with my hazards on, and people having to drive around me, expecting I'd have to call out breakdown cover, when I tried again, it turned slowly, then started. Slightly before that, I'd noticed a little smoke from the side of the bonnet. After that, I drove to my destination, everything seem fine, when I got there, I had a look under the bonnet, and could see no rhyme or reason for the trace of smoke I saw.

Needless to say, ever since, whenever I've had it rev like that in traffic, I've never turned it off, I've always managed it some other way.

No idea on that car, looking `at the live readings would be revealing.

Has it got the irritating VAG failure mode where the engine management temperature sensor is completely seperate to the dashboard one?

Not sure about that until I look into it more. The temperature gauge seems to behave normally, and settles in the region that other owners say is normal (always stays a little below halfway - I'd normally think that was suggestive of the thermostat needing replacing - but it appears to be normal for the model).

Just seemed to be frequently mentioned as the fault for plenty of similar symptoms, from googling it (CTS, that is). That said, so is the TPS. I think when I experience it happening again (still awaiting the fault code reader), and I've got an opportune moment to stop, I'll see what unplugging the CTS and TPS does to the idle behaviour.