erratic idle speed question

[RichL]

I've had a 3000rpm idle once or twice caused by the intake pipe coming loose between the airflow sensor and the manfold. It could be something similar on your motor, but the fact its not a constant thing makes me doubt that and point to something electrical or a sensor.
It might be a split in the rubber hose or a the hose come loose at one end, and when the engine rocks it causes the split to open/close and give you the high idle speed, but I doubt it.
I'd be VERY wary of disconnecting the battery for 5 minutes and 'cold booting' the ECU on a modern engine. Higher end management systems are sometimes adaptive and more or less 'learn' how to control the engine. A workmate had the battery go flat on his Daewoo, and after recharging it took 10 minutes before it would idle properly, and drove like a bag of poo for the next 20 as the ecu gradually came back online. After that it was fine.

[dave m]

OK, I'll look for splits, loose hoses etc first. Mind you it seems like my system has already forgotten how to control the engine
When it's behaving it runs fine and can do so for days at a time, then just as I think the problem has gone away it'll be a real pig again

Dave

[Dogbert]

I had the EXACT same problem with my car. Check the idle speed control valve.

[dave m]

Will do

[mutz]

...been through a car wash lately? Cold rainy weather? (UK, silly question)

Could be something got wet and/or you have condensation in the electronics...

[dave m]

Interesting...

I got home tonight and the revs climbed up to nearly 3000rpm, I wiggled lots of hoses with no result. I rapped the top of the inlet manifold, where the throttle control (slack so not that sticking)and various electrical connections are, with my knuckles (I don't have a decent service manual, so I don't exactly know what is what) and the revs instantly dropped to a ropey 300 rpm. I then wiggled the electrical connection into what I am guessing is the idle control valve and it instantly jumped to a stable and smooth 750 rpm.

So it looks like the problem was the idle control valve, and with any luck it was just a bad connection. MURC does it again!!

My warranty ran out on Tuesday so I was hoping it wasn't going to be serious, let's hope that was all it was. If it's more serious at least I know where in the engine to look,

Thanks all,

Dave

[Rags]

Dave, what kind of car is this exactly?

2.5 DOHC 24 valve V6 doesn't say much, really. Is this a Ford product?

Rags

[GT98]

Originally posted by Rags
Dave, what kind of car is this exactly?

2.5 DOHC 24 valve V6 doesn't say much, really. Is this a Ford product?

Rags

Kia Sedona

[dave m]

Actually it's Korean, a Kia Sedona, but I believe it borrows it's engine design from the newish Rover 75.

GT98, you just got in there while I was posting this.

It's built like a tank, lacks refinement, but does what we need it for.

Dave

[efty]

I have the same problem with my car Mitsu Eclipse 94.
The idle speed valve is busted. The funny thing is that the car when rested for a couple of hours it works fine for a few minutes. Then the trouble start. It will not let me go above 2000rpm. It feels like air brakes are being applied. The stupid thing costs almost 300 dollars to replace and I have already spend too much on this shitty car. One day I will take to the hudson car wash and get done with it.

What is rather strange is why it works for first few minutes and then it acts up.

[Rags]

Then that motor in the Kia is the corporate Mitsu V6. If it's the same electronics like in the US, which it most likely is, then I would be diving for that Idle Air Control Valve. They have problems with them big time, also I wouldn't rule out a connector pin problem, the Kias are notorious for having pin pressure problems where the pins won't flow the current properly, removal and replacement or tightening of the connector pins seems to do the trick.

Rags

[Rags]

Originally posted by eftychios
I have the same problem with my car Mitsu Eclipse 94.
The idle speed valve is busted. The funny thing is that the car when rested for a couple of hours it works fine for a few minutes. Then the trouble start. It will not let me go above 2000rpm. It feels like air brakes are being applied. The stupid thing costs almost 300 dollars to replace and I have already spend too much on this shitty car. One day I will take to the hudson car wash and get done with it.

What is rather strange is why it works for first few minutes and then it acts up.

You engine won't rev above 2000 when warm?

Your idle air control valve should have no effect on that, since it is metered air.

Rags

[efty]

A mechanic cleaned the motor's carbon(?) and it worked fine for a few days.

It is possible since it is a stepper motor to cause the problem. Most propably gets stuck at a position not fully open thus not enough air is entering the combustion chamber. When this happens the check engine light comes on and the exaust air is not clean.

I am no expert but what else could it be with this symptoms?

[dave m]

OMG!!

Must have been a dodgy connection on that idle valve, today it's a totally different car. The engine is smoother, livelier, much more responsive and accelerates away at much lower revs than before. I'm beginning to think that valve was playing up before I even got it (as an ex-demonstrator with 6,000 miles on the clock). Previously there was always a bit of hesitancy in acceleration with full power not cutting in until you hit 4000 rpm when it would take off as if a turbo had cut in, now it pulls away smoothly with the power building up from the word go.

With any luck it looks as if it's fixed, but at the weekend I'll probably take the connector off and check the pins and sockets to make sure they're tight.



Dave

[Rags]

Originally posted by eftychios
A mechanic cleaned the motor's carbon(?) and it worked fine for a few days.

It is possible since it is a stepper motor to cause the problem. Most propably gets stuck at a position not fully open thus not enough air is entering the combustion chamber. When this happens the check engine light comes on and the exaust air is not clean.

I am no expert but what else could it be with this symptoms?

Not the IACV. But what model of Mitsu eclipse is this? Turbo? 2.0 DOHC?

Rags