Hi guys, I'm new here.

I have an EF Fairmont S2 that I have converted to manual using futura donor including ECU about 5yrs ago.

It had developed the slow to return to idle(800-900) just before XMAS especially when the AC kicked in and out. It once ran away to over 3000 whilst sitting at the light so I turn it off fast and restarted without the AC.
Scary.

Then the clutch cable pulled through the firewall so I left it with the battery disconnected for 2-3 week over XMAS until I could get a mate and the Mig over to fix it.

Once fixed, I started the car and it idled at 2000-2500 so I disconnected the ICS and drove like that for a day. I though the ICS was wornout.

I fitted a "NEW" genuine ICS and the F$%^& is just as bad if not worse.
When changing gears the revs (2000-2500) dont drop unless I stay in neutral for an extended period (10-20 seconds). They drop to 1100 ish then 2 seconds later they drop to 800-900.
When the AC is put on it struggles quickly to 1000.
I disconnected the battery and reconnected it to do the 5 min self tune but no good.
The ICS has a purpose and once worked fine so "What the?"
By the way the car is stock so there are no mods interfering with the ECU.
Can I clear the ECU back to default value if this has just tuned itself to madness?
Is it a fuel issue or the O2 sensor is the cause?
Injectors dirty?
Had the brakes done at an exhaust place today and he said he was surprised the original exhaust was still on after 200,000K and suggested it was running lean, which supports one of the posts above.

There must be some cluey bloke here who has battled this and won!

With the ISC disconnected, how high was the idle?

Also, could be a problem with he ECU, or one of the sensors.
Run a diagnostic and see if you pull any codes.

do a diag, failing that, theres a new fix for i6 ecu's having to do with capacitors ( http://www.fordmods.com/forums/viewtopi ... highlight= ) i doubt it is the oxy sensor because even if it is a bit off it should be able to compensate. but after 200,000 it'd be worth replacing. have a quick squiz at this too, explains a bit.

i'll put my name to it that the fuel filter is plugged up to the s**t. replace the filter, plugs and oxy and then reset the ecu again. i think she'll run like new

and welcome to fordmods

Thanks for the fast response and welcome guys.

I have since done a search and looked at a lot of posts to do with idle issues and there are a lot of suggested causes.
My idle with Idle Control Solenoid (ICS?) disconnected was 800-900 which was the norm before the problem.
I will run a diag when I make up a box of diodes and switches after digesting the sticky about this. I wonder if a plug for the ford socket is available?
Another post rightly pointed out the diag will show a stuffed sensor but will it show one operating out of normal range?

My next move will be a quick look at the MAP for a loose/stuffed hose tomorrow when there is light.

Thinking about the O2 sensor, would it not affect only closed loop tuning?Not the holding onto revs.

If it was the spark plugs would it not "miss" but would it affect holding onto revs.

Fuel filter would affect outright accelleration/performance? No issue there.

Just thinking out load and trying to be logical.

If the failed Capacitors in the ECU prevented the ICS from performing properly buy limiting the PWM power to the ICS, this may prevent it shuting quickly when the throttle is released and the ICS is slow in controlling the decent of revs back to idle. Emissions thing where the hydrocarbons are burnt better if you don't snap the throttle shut.

Thanks again.
Cheers

Well your base idle sounds a bit high anyway, which doesn't help. Try lowering it to 700rpm.

http://www.fordmods.com/forums/viewtopic.php?t=41564

&

http://www.fordmods.com/forums/documents.php?doc=52 (shows you how to read faults without the special box)

and i think you should check the fuel filter, you'll be suprised i think. it's possible that it hasn't been swaped out for over 100,000k's. and i know a fair bit about the different types of fuel and believe me, i put my money on it that it could be clogged.

thing about it is, the isc activates when it sences the revs drop and it incrimentally checks the oxy sensor, when the revs are dropping if the tuning is lean the computer will read a better AF ratio of 14.7 when the revs are dropping because there will be less air and the same amount of fuel, telling it to idle a bit higher and thats why the revs wont drop back. it will actually be in perfect tune for a split second after the foot comes off

is it normal for the car to stall when the isc is disconected when the engine is up to normal running temp.

hi
im pretty sure the idle should be about 500 rpm with the isc disconected.

so i would run your car with the isc disconected and adjust your idle down to about 500 rpm and plug the isc back in and it should be ok...

i think it is, but i couldn't be sure

No, you generally want it to be able to idle without the ISC.

have you checked your power steering pressure switch? if that is dead/leaking that can cause idle problems as i had found with my car.
bloody things :S

Yes the car should stall or come very close to it with the ISC disconnected. If it idles right with the ISC disconnected then you have the idle set too high and will get all sorts of problems like slow to return to idle speed, high idle, erratic idle, etc.

The ECU always wants to control the idle by the ISC. That is why the idle speed without ISC control needs to be low. The ECU will always try and leave the ISC open a fraction when backing off the throttle. If you have the idle speed set too high then of course the idle is going to be slow to return!

Before hacking into your loom installing a switch to disconnect the ISC, set your idle properly!!!!

Get car to running temp. Stop engine and disconnect ISC. Place a 0.75mm feeler between the throttle stop and idle speed screw. Set idle speed to 650+-50 rpm in drive. Turn car off and remove feeler and re connect ISC cable.

If your ISC is not stuck your car will idle fine. It will start right, it will return to idle quickly. If it doesn't then you have a vacuum leak somewhere or some other problem.

Anyone who says your car should idle fine with the ISC disconnected WITHOUT adjusting the idle speed is just plain wrong.

cheers
Scott

The point is the car SHOULD idle without the ISC, regardless of whether it does out of the factory, or if you have to go out there and adjust it.

It shouldn't stall, but it certainly shouldn't be any higher than say 700rpm either unless you plan on disconnecting it.

I've experienced bad hunting issues with having idle set too low, and hanging with having it set too high. The perfect medium for me is around 600-700rpm, just as you also suggested.

Yes it should idle without the ISC IF you turn the idle screw up. If you don't want the functions of the ISC; air con power up, power steer power up, cold running power up, then by all means unplug it and adjust your idle speed to suit.

BUT if you simply unplug a correctly adjusted ISC then expect your car to stall or idle extremely low and hence very rough. You cannot expect a functioning ISC to be able to run a car correctly when the base idle is set at 650rpm with the ISC disconnected. It just will not happen. You need that feeler guage in there to give the ISC some working room. Period. No ifs, no buts.

cheers
Scott

Runs fine for me man, if I set it any lower it hunts.
Although I'm quite happy to accept the fact that cammed cars do not behave as stockers do.