idling problem

[Struggler]

So the car idles lovely, but in the wrong place! it sits at 2500rpm,
then sometimes lowers itself to 1500rpm,
its not lumpy or anything, when driving its pretty much fine,

dip the clutch in any gear and the revs drop to around 500rpm, then goes back up to 2500rpm?!

ive been told that it may be a cracked inlet but i would have thought the idle would be lumpy, and wouldnt drop to normal idle point before rising!!
im thinking its possibly the idle control valve playing up and needs a clean, so im going to do that tomorrow.

any other suggestions??

 

[sideways danny]

3 common issues, and a couple of less common ones.

first there's a speed sensor earth that goes to the back of the dash clocks, if it's corroded or broken it confuses the ECU.
then there's a sticky idle control valve, remove, soak in brake cleaner, the lubricate well with wd40.
Thermostat, if the engine doesn't get up to temperature properly you'll keep reverting to cold idle conditions and this seems to make the F7's rev to closer to 2k.

If none of those fix it, you're going to need to start investigating for vacuum leaks

 

[Struggler]

how would i know if its a thermostat issue?? would the water temperature not give it away?? because it was sat spot on nominal.
and it was after a bit of blast so i would have thought it would get up to temperature reguardless if the stat opened or not?

im worried it is a vacuum leak since only friday i converted to manual steering that obvious gets rid of one of the inlet manifold supports.

im going to get some carb cleaner tomorrow and sray it all over the inlet manifold and see if that gives away if ive split the inlet.
and soak/clean the idle control valve.

ill look into this wire behind the clocks, how will i know what wire it is??

thank you for replying btw

 

[sideways danny]

just change the stat, it's an annual service item IMO, bit of an issue with the seals falling apart too

 

[Struggler]

thank you, ill pick up/order a new stat when i go to the motorparts tomorrow to get some carb cleaner

any advise on this possible corroded wire behind the clocks??

 

[sideways danny]

never had to do one, but it's well discussed on the mk1 forums. Better place to ask really

 

[Struggler]

ahh thankyou, ill look into it!

 

[huizit]

could be an air leak, i had this on a previous car

 

[MicKPM]

Nagh, I doubt its an airleak and think Danny has hit the nail on the head with either the speedo earth (It's part of the speedo cable IIRC) or faulty IACV.

Its not very often we get to see the older cars these days but I've just had to do a friends Williams 1 that had similar issues and that was IACV

 

[Struggler]

ok did a quick test,

with the throttle i blocked the idle control valve with my hand.

the revs dropped but the car seemed to still run,
also thought i could see a bit of the inlet gasket handing out the bottom of the inlet,
going to spray the inlet with easystart first tomorrow as this will confirm that it is an airleak