High Idle Speed

[H474YGF]

Sometime, pretty much always when cold and occasionally when hot, my stupid 16v idless at about 2500rpm. Its quite random and very annoying.

Its not the throttle cable or switch. I was thinking it could be a faulty idle valve but I'm not convinced of that either. Did I once read that the engine management will increase the idle speed when the battery voltage drops too low? The car does have some dodgy wiring around that battery...

[Vanny]

dont know about a low voltage causing a high idle, but there is a temp sensor in the thermostat housing which will up the idle speed when cold, but not typically by that many RPM.

[Mike P]

I would suspect the ICV.

Mike P.

[H474YGF]

The temp sensor seems ok. As you say it wouldn't make it do that anyway even if it thought the engine was freezing! I swapped the idle valve and, unless I have two identially broken ones, its not that either. Its definately the engine management deciding to rev it that high as you can tell by driving it for a while.

Mystery. I'll have another look today.

[RobC]

i had this once. never got to the bottom of it. then one day it just stopped doing it as suddenly as it had started doing it in the 1st place...

probably some wire/connection somewhere temporarily shorted or sommat.

[thanuttiscotsman]

hi there,
i had this for years and couldn't solve it with 1 of my 16v's. turned out to be the ecu at fault, have you tried another ecu?

rossco

[H474YGF]

Well there is an easy way. Without the cable connected it runs OK. Its sluggish when you start it but then, after a few seconds, its OK. Sod the ICV!

I had them (the idle valves) both on a variable voltage power supply and watched the valve open and shut. One of them was a bit jerky but the other seemed nice and smooth.

I did have a spare ECU but cant remember where I put it. I think its at my parents house somewhere!

I had another problem this week too. Actually I had three but I'll let you in on one of them. The pulley the air-con belt goes over has knackered bearigns... that bad the pulley now rubs against the mount causing a right racket. So you can sit here and read about how I cheated my way out of it or let yourself feel great in case this ever happens to you... Because we all know sh*t happens... with these BXs and stops us enjoying ourselves... which is why we go on these forums... So I went to Halfords... not my favourite shop... with a bicycle inner tube cut to the length to make it over the main pulley and just the alternator. A good start I thought... and then I asked the nice chap to go and find me a belt with five teeth that was the same length... and the jolly chap came back with one... and you know you feel great when things just start working out like that. And the guy said are you happy with that and I said yes I think I am happy with that because You, like me love it when you find a fix that gets you out of a hole. Any way the car feels great and runs OK now so we are happy. Because we like to be happy dont we? I do too...

[Timmo]

one thing may be worth a try is cleaning out all the breather pipes that run onto the tb and inlet pipes as they could affect your idle a smidge, and also with the engine off, lift the throttle bit and check your throttle position senser clicks when its returned to the stop, if yes thats okay, if not that could also be an issue!
if you say its okay wioth the cable of then it may be worth loosening of the cable a bit through the odd thing that holds the outer tensoin where the cable comes out to the butterfly attatchment!??!

[Toddman]

Also worth checking the plug that connects onto the AFM - Clean the pins on the AFM and the pins inside the plug can benefit from being tightened up by pushing them together with a small screwdriver making a much better contact onto the AFM.

Another very common problem is the TPS not being hit when the throttle is closed as this switches the ecu into idle mode and without this happening you will neve rget a decent idle.
The TPS is the pack on the side of the throttle body and is basically 2 micro switches one to trigger idle mode and the other for full throttle mode.

Cheers
Luke