was having a spot of trouble with my car, it would hunt around for idle, and recently it started idling really high, from cold and stayed high when it was warm.

i removed the iscv, cleaned that, and also removed the throttle body and adjusted it to 0.25v @ no throttle. (by the pins on the ecu, it was previously at around 0.1v.

when i put it back together, it still idled high, so i closed up the throttle screw, and this had very little effect. but when i unplugged the iscv it dropped to 500 rpm. i then adjusted the CO screw, by a few turns to get it to idle @ 900rpm (adjusted without a exhaust analyser , so i have no idea what the co level is??)

could it be a fult in my loom, cos when you plug in the iscv, even when warm, the revs jump to 1900 rpm

took it out for a test drive, was wary of going on boost (or is this unaffected by idle and CO, used to rs turbos adjusting anything can mean bang if not done properly)....but it did notice the throttle feels better, less twitchy and they revs dont ever drop past 900 rpm when you slow down, before they used to drop and rise??

please help me guys. criticise me, or help me.

its due for its mot now....thats why i am doing all this

cheers

 

bttt

its in for the mot today

 

it passed is mot

turned the co down to 2.5% on the ecu, to pass, what affect does this have on the engine, on boost etc?

i am now running it without the iscv connected and its idling really low, at about 700 rpm. but when i plug ir in it goes back to 1600rpm

anyone got a solution? what governs the iscv???

please

 

Ginge......

You have to adjust the idle with the engine at operating temp and the ISCV disconnected,set the idle to about 900 and re-connect the valve....

 

when i reconected the valve the engine speed jumps up anyways?

even with the engine warm

 

Maybe an iffy valve then.......You got another to try ?

 

its unlikely to be the valve at fault, the system is driving it on, probably not fully on, but on some. The base idle does need to be adjusted by the air bypass screw under the throttle to idle at 850-900rpm when warm WITHOUT the iscv connected. When it's correct the engine speed shouldn't change when you plug the valve back in. By the sound of it though, yours jumps straight back to 1500rpm when you plug it in irrespective of the other conditions
ECT faults which make it idle high would also make it run rich, which it doesn't sound like it is.. You've adjusted the throttle sensor now which is the normal cause of high idle on 4x4 L8, so its a bit of a mystery (assuming here that you do actually have a L8 ECU and PF09 throttle sensor and 4x4 engine loom?)
If the base idle is set properly and CO settings are adjusted suitably (maybe a bit richer than the 2.5% that you have) then it's likely it will be ok in normal use without the iscv connected, with warm engine at least.

 

well at the minute, the CO is set to 2.5% @ idle

the engine idles @ approx 700rpm

for some reason the idle valve is permanently open, whatever governs it, is keeping it open?????

need to get this sorted asap??

 

a lot of cars have iscv disconnected.

i'm going to try & talk to someone about the problem a bit later Rory.

 

if the idle speed is 700rpm with the valve disconnected, then the base idle setting is too low - you need to raise it to 850-900rpm (warm engine) by adjusting the air bypass screw under the throttle body, before you do anything else

 

i know the mondeo can suffer with idle problems due to the power steering sensor.
prob no help to you at all though

 

will have a go at this today

wont touch the CO screw as i dont have an analyser here, but will try and raise the base idle a little.

would like to know whats causing the iscv to be permanently open though???

 

i had this with my old cossie was just driving along one day came up to a juntion and the revs wouldnt go below 1800rpm disconnected the idle valve and it went back to normal again as soon as i connected the idle valve back up hot or cold it would go to 1800 rpm and it turned out to be a broken wire going to the throttle position sensor as soon as i fixed the broken wire by putting another plug on it was fine.....

so have a look mate might be wrong but its worth a look

 

i am starting to think that it may be a wiring failure.

thats why i need to know what governs the iscv.

so many wires though, what a headache

 

please can somone tell me what controls it???

could the TPS be at fault?? or just the wiring, and how do i check it?

i wanna get this sorted before i take it back to scc to get the CO adjusted back after turning it right down for the MOT.

 

BTTT

 

where did you measure the TPS voltage? Back at the ECU plug, or locally at the TPS? Either way it's unlikely to be TPS, as you are actually measuring the correct voltage. If you measured back at the ECU then that proves the wiring also..

 

i measured it at the back of the ecu.

will do a full sweep of the tps to see whether its reading or not, over the full range....is it 0-5V?

what wires from the ecu give the output to the iscv? can check this too?

 

Mine did this a while back ginge, I went my me local garage and they stripped the throttle body down, cleaned it all out, cleaned the ISCV and put it back together and it was fine after that. Major build up of ack and grime had made the throttle linkage sticky. Could be the problem

 

put a secs monitor on it, then you will see if the throttle positiom switch ,ect sensor etc is all working

 

Pin 34 is the ISCV earth pull on the ECU

HTH

 

Sounds like TPS failure to me, however, i have seen issues like this when there is TOO MUCH voltage at the valve itself. A customer had a real mare with one like this and pinned it down to EXCESS voltage at the ISCV after rewiring a fuel pump.

 

Rory, when you've investigated it a bit more, if you think its to do with the throttle body/tps etc, i have a brand new one if you get stuck.

 

well i have cleaned the whole throttle body isc so it isnt dirt.

it could be a TPS failure. GUZZLER, could you PM me with a price on the 4x4 TPS, if its cheap cheap

SECS has been very helpful in helping me diagnose it, and i have few more tests to try tonight.

at the minute the TPS is reading 0.25v@idle so is working, but something is sending a signal to open the iscv fully? even when warm

will check pin 34 on the ECU to see if it varys? where does the other wire from the iscv terminate? at the tps?

i have been told to bridge the tps at the ECU and then try and start it, should i do this with or without he iscv plugged in?

cheers for all the help and advice guys

thats why i love this forum

 

the other iscv wire (black one) is a constant main relay fed 12V supply, that also feeds Amal valve and injectors.
By all means try changing the TPS, but if the ECU is seeing 0.25-0.3V TPS signal voltage at idle, then that's all that is needed as far as the iscv operation is concerned with regard to the TPS signal.

 

the ecu IS seeing 0.25v @ idle , but the iscv is permanently open??

so there most be something else causing the iscv movement. or a wiring fault.

when i set the CO on the car, should it be with the iscv plugged in??

even if it causes the revs to rise to 1600rpm?

 

no, you're right, there IS evidently something forcing the iscv drive, or making the system think it needs a fast idle..
OR - as you say there is a fault.. I'm just trying to clarify the position with the TPS to avoid you chasing problems that aren't there unneccesarily.
Simon SECS is probably best placed to understand the conditions that would make the system think it needed a fast idle.
The other possibility is that the iscv drive output stage in the ECU is broken, forcing a permanent earth on pin 34 and driving the iscv on all the time - hard to know without looking at the signal with an oscilloscope to see if it's permanently low or switching (as it should be). Try briefly shorting pin34 to chassis with a length of wire whilst it's running and see if the idle raises even further - this would indicate if the valve is being driven hard on or only part on..

 

well as far as i was aware, when checking before, i plugged in the iscv, when it was removed from the engine and it just popped open, looked like full displacement.

in theory, if i put a voltmeter on it, as the car warms up the output voltage to it (measure the plug that goes on it) should drop as the valve is required to close????

this may give some suggestion?

will try fitting a new tps sensor, but dont see what this will achieve, as it will be set to the same voltage @ idle.

will try and skip off work early and get to the bottom of this tonight

will try all of the advice given here, and the help from simon@secs

 

the iscv gets driven by a pulsed waveform (one terminal of valve has 12V supply, other terminal pulses low driven by pin34) - if you measure pin34 with a multimeter with respect to ground, what you will measure is the "average" voltage drive determined by the on/off ratio - as the valve drive reduces to close the valve, the average measured voltage will increase and conversely as the valve is driven open the average voltage measured at pin34 wil decrease
This may seem odd, but it's due to the active "on" signal being low.

 

so to summarise the voltage should start low, and raise as the engine warms up?

is it ok to measure the pins on the connector? with a DC multimeter.

if it doesnt change i can assume the valve is drive open ALL the time and there is afault somewhere?

 

yep, that's about right.
The actual voltage value you measure with a dc multimeter will indicate if the fault is with the ECU output driver, or elsewhere in the system.
A broken ECU driver stage would show as a consistently very low (approaching 0V) value. A strong pulsed drive signal, capable of holding the valve well open, will show as an average value somewhere appreciably above 0V.