Crazy high idle?

[chieflief]

Hey all. Just went for a quick blast, couldn't get the idle down below 1.5K, at times it was a steady 3K. Anyone know what's going on and how I can fix it? 1996 S1 stock. Cheers!

[Pabl0]

More details would be useful but suspect IACV. May need cleaning or replacing.

[kambites]

When I had this, it was a dodgy temperature sensor connector.

Be wary until you know because if you have a loose connection to the temperature sensor, the ECU can spontaneously decide to introduce a 4500rpm rev limit, which isn't much fun if you're at 6000rpm in the middle of a corner. The S1 might be different, mind.

[Thorburn]

Also worth checking the throttle body and throttle cable/linkage aren't sticking.

Had this on mine due to the bush in the throttle linkage wearing, allowing excess movement of the linkage on the pivot and the cable pull getting caught on the plate the linkage is attached to. Greased up the throttle cable at the same time as it wasn't pulling through particularly smoothly, so the cable was drawing back slowly if you snapped shut the throttle, resulting in a brief flare of revs on gear changes.

[davidf4]

Check that the throttle cable isn't sticking in its insulation at the engine side. It could be holding the throttle open. A squirt of WD40 and a little mananual throttle operation to work it in freed mine up when it did this.
Some of the bits and pieces in the engine bay are exposed to the elements through the engine lid grill and damp and crud can get in and build up.

[chieflief]

I WD-40d the throttle cable - seemed to have done the trick, although it does settle at about 1200RPM. What should 'normal' idle be?

[kambites]

chieflief said:

I WD-40d the throttle cable - seemed to have done the trick, although it does settle at about 1200RPM. What should 'normal' idle be?

About 1200rpm when cold and 800rpm when warm, I think.

[John D.]

Pabl0 said:

More details would be useful but suspect IACV. May need cleaning or replacing.

Sounds like when my IACV was sticking on my S1. More frequently it wouldn't idle at all from cold then would be fine once up and running/warmed up. Once or twice it did stick at a very high idle, which would creep higher and higher (rather embarrasing stuck in traffic in town!). Could usually 'fix' by stopping, shutting off, and doing the TPS reset procedure.

Cleaning it didn't help. New IACV sorted it.

[chieflief]

John D. said:

Pabl0 said:

More details would be useful but suspect IACV. May need cleaning or replacing.

Sounds like when my IACV was sticking on my S1. More frequently it wouldn't idle at all from cold then would be fine once up and running/warmed up. Once or twice it did stick at a very high idle, which would creep higher and higher (rather embarrasing stuck in traffic in town!). Could usually 'fix' by stopping, shutting off, and doing the TPS reset procedure.

Cleaning it didn't help. New IACV sorted it.

Took the car for another drive; the revs won't settle below 1500RPM - although it DID, ONCE, at a thoroughly acceptable 800RPM. Have looked at http://wiki.seloc.org/a/Idle_Air_Control_Valve, and will have a go at cleaning it. Will let you know how I get on. Thanks for the help.

BTW there is a definite petrol smell in the cabin after a fill up (until the tank is about half full) - might the two be related?

[John D.]

chieflief said:

Took the car for another drive; the revs won't settle below 1500RPM - although it DID, ONCE, at a thoroughly acceptable 800RPM. Have looked at http://wiki.seloc.org/a/Idle_Air_Control_Valve, and will have a go at cleaning it. Will let you know how I get on. Thanks for the help.

BTW there is a definite petrol smell in the cabin after a fill up (until the tank is about half full) - might the two be related?

Dunno. My S160 stunk of petrol as soon as you gave it proper beans

[chieflief]

I cleaned the IACV (very sooty), made sure the throttle body butterfly valve was working properly, gave the entire throttle cable a good soaking in lubricant... and it's still not completely right. By twisting the part by hand where the throttle cable ends (tightening the throttle cable; in the photo the black part on the left), I can make the car idle at 800rpm (when warm of course). But after kicking the revs higher, it will only settle at about 1500rpm.

What is the three pronged plug on the right in the photo? I think the problem lies there; I pinched more closed the points of contact for the plug, cleaned them with electrical contact cleaner, and it seems slightly better. By really pushing the plug in, I can make the revs settle at 800. Taking it for a short blast it now settles at 2000rpm, but can now blip the throttle and it will settle at 800rpm nearly all the time (well, during that short blast, anyways).

I know it sounds contradictory, but let me clarify: I without intervention, the rpms settle at 1500 after revving the engine by hand, but on the road the rpms settle at 2000. It doesn't quite make sense to me either.

What I do notice is that the revs decay very slowly when the clutch is depressed (or when in neutral). For example if I shift from first to second at 3000rpm I can get in to second at the same rpm; similarly from second to third, etc. No need to double-clutch! I can link a video if it would help clarify the symptoms.

[kambites]

chieflief said:

I know it sounds contradictory, but let me clarify: I without intervention, the rpms settle at 1500 after revving the engine by hand, but on the road the rpms settle at 2000. It doesn't quite make sense to me either.

Sounds believable. The idle speed depends on how fast the car is moving (at least on my S2). If you're travelling at above about 10mph, it idles about 1100rpm, if you're not it idles at 800. Not quite sure why, some emissions oddity, I suppose.

[chieflief]

So according to a friend's mechanic, it's the potentiometer (the thing that plugs in to the three-pronged part I mentioned earlier) that is likely at fault. Will try to find a replacement somewhere and see if that fixes the problem. Anything I should be aware of when fitting a new one?

http://en.wikipedia.org/wiki/Potentiometer

[BernB]

chieflief said:

So according to a friend's mechanic, it's the potentiometer (the thing that plugs in to the three-pronged part I mentioned earlier) that is likely at fault. Will try to find a replacement somewhere and see if that fixes the problem. Anything I should be aware of when fitting a new one?

http://en.wikipedia.org/wiki/Potentiometer

That could well be the problem - I had similar high idle issues when I replaced the throttle body on my elise, and forgot to connect the TPS (Throttle Position Sensor) back up.

You could try removing it and spraying it with some contact cleaner to see if that fixes it.

When you fit it again (or a replacement), you'll need to do a manual recalibration :

http://wiki.seloc.org/a/Throttle_Position_Sensor

[chieflief]

BernB said:

When you fit it again (or a replacement), you'll need to do a manual recalibration :

http://wiki.seloc.org/a/Throttle_Position_Sensor

I didn't need to replace anything in the end; it just needed a quick recalibration, as mentioned above. It's completely sorted now.

And a pint it is for you, Mr BernB... next time you're on Vancouver Island let me know.