jonnyc

Hello everyone.
Got an issue with my cossie idle speed again.
Took her out the other night and when i got back My idle speed was resting at 15oo rpm. Took iscv out and the plastic disc moves freely up and down the shaft. Made no difference to idle speed whether iscv was connected or not. Hot or cold engine starts and slowly rises to a resting idle of 1500 rpm.
Sprayed hoses with wd40 and no rise in rpm so no leaks pressent. Fitted a MD wasted spark kit 2 weeks ago but dont think this would affect my idle speed would it?
saphire cosworth 1992.

JonathanJ

Air leak would be within the inlet manifold not hoses around intercooler , have you tried screwing the idle speed screw in (underneath the throttle body ) ?

mpales

Tps has two small screws!!!!! attached to the butterfly and sometimes these bolts loose!!!!! and the tps goes out of scale!!!!!and the result is that the idle speed increase..usually everybody think thats is the iscv...other think that is the screw under the butterfly..

tabetha

The plastic part is not the problem sticking wise, often the actual shaft sticks in the iscv.
If it was ok before idle wise and it is now 1500 rpm, then this suggests the base idle is correct as it was before, unless of course it's come loose.
This leaves us air getting in through a stuck iscv or through a leak, as it needs the air to raise the revs over what the throttle body bypass gives air wise to set the base idle speed.
You could use a wood dowel to block the hole the end of the iscv goes into, this will ensure the only air it should be getting is via the bypass screw, some just use a big wadge of bluetak to temporarily block, if this then idles at the speed it used to, you know it's the iscv at fault.
The WS kit could conceivably give a tad higher rpm as it is making a more complete burn of the fuel, but wouldn't account for 500rpm increase, and would have done it right away.
tabetha

jonnyc

I will try the blue tac trick. when i dissconected the map sensor the revs drop back to 800 but the engine runs bumpy. does this indicate the map sensor is ok cos a mechenic at an old mans garage told me that this could be the issue. is this plausable?
This forum is lucky to have knowledegable people like you mate.

jonnyc

Just done the blue tac trick.. Engine still revs at 1400-1500 rpm hot or cold. I guess this rules out a dodgy ISCV being the culpret?

rscos2004

Have you altered the mixture screw on ecu as this can turn youre revs up as mine was when first fitted l6 ecu.

martysmartie

iTrader: (1)

No you must have an air leak somewhere this is the sole way the engine speed can increase, maybe the inlet manifold gasket?

A sensor cannot cause a high idle directly but it could indirectly if it tells the ECU duff information which in turn gives an output to ISCV to open to raise revs, you have eliminated that by disconnecting the valve, the only other way is through throttle or the air bypass screw, either that or throttle is sticking open so check cable is free etc, disconnecting the ISCV would have sufficed, unless you suspect it had stuck open.

The car won't run at all without the MAP sensor runs lumpy as it's running rich, it probably would have cut out after a while especially if you tried to drive it.

Martin

jonnyc

Where is the screw on the throttle housing? do you mean the control/adjustment screw cos surely this would loosen outwards which would decrease the revs?? I have not adjusted the mixture screw on the ECU. I have disconnected every small hose and covered their manifold connector with my finger with no change. I will disconmnect the big intercooler hoses and check the plennum is not partialy open.

I love being a cossie owner. Cant believe how tempramental they are.

martysmartie

iTrader: (1)

There is a screw on the throttle housing this is the "Base idle adjustment" the idle speed cannot go BELOW this but can be raised using the ISCV. (Make sure nut is done up properly if ever adjusting this as many have fallen out from not being tightened after and there not cheap to replace/source)

2WD you need to undo the locknut first with spanner then adjust screw as you correctly say anti clockwise will decrease revs and clockwise will increase. However this isn't your problem seen as it hasen't been adjusted and was ok, so you either have an air leak or the throttle is sticking.

When these cars run they are very reliable, however as with anything old expect age related problems from time to time.

Martin

jonnyc

Tried the screw but it was set full clockwise and wouldnt turn anymore. When i turned it anti clock the revs went up as they should.
Booked into ford tommorow. I give up!

martysmartie

iTrader: (1)

Try disconnect the ISCV again (Not actually removing) if it still continues after this it will be am air leak or throttle stuck open.

Martin

jonnyc

dissconected the iscv at the grey plug and no difference. Sprayed every surface on the intake side with aerosol and it does not increase revs. maybee the spray is not a sure way to tell for intake leaks. Just been out in her and it still pulls like a train under full boost with no hesitation. I checked the plenum screws today and the butterfly plate is solid. Checked for obstructions keeping the plennum open but found nothing. Its a mystery.

cozmeister

iTrader: (1)

I'd put money on the inlet manifold gasket...

Did it happen all of a sudden or has it got gradually worse?

martysmartie

iTrader: (1)

Did you spray it around the plenum elbow as well I.E behind the throttle body?

Martin

jonnyc

it happened all of a sudden. I think i went over two pot holes and having konis it really gave the car a good thud.

jonnyc

Ford have given up also. Not able to diagnose issues with cars fitted with aftermarket bits fitted.
Stu at MD recons dump valve knackered or plenum gasket gone.
Which dump valve would I use on stage 3 t34.

cozmeister

iTrader: (1)

Can't go wrong with a Bailey one.

martysmartie

iTrader: (1)

Yes that is possible, easy to test just remove dump valve, and plug it with a cut down broom handle, the diaphragms split in them after so long.

To be honest I don't think Ford would have a clue what to do now, it's not like a modern car where they can plug computer in and read the fault codes and then act, sadly most true mechanics have now gone.

Martin

jonnyc

I have removed the inlet pipe between the intercooler and the throttle housing. When i cover up the hole inside the throttle mouth the revs drop to 800 which is perfect. am I right to asume that if there was no leak behind the butterly then the engine would stall and because it dropped to where it should be this indicates either that the adjustment screw is worn (unlikely) or that as someone said above, the plennum gasket is shot.
who needs Ford anyway!!!!!!!!!!!!!!!!!!!!!!!

rscos2004

Most of the people in fords wont have a clue what to do do i had that problem with my merc 300d at main dealers.