[ShadowWorks]

I just cleaned my throttle plate and intake body yesterday and something strange has happened.

when i rev the engine above 1500rpm and the revs drop, the rpms stop at 1200 and then slow climb down to 950 rpms.

I have seen my brothers Honda do this so i though fine, its an improvment because before when i boosted and then came out of gear and coasted my 900 i could almost stall it and have done so before but now when i coast the engine speed stays at 1200 rpms and does not go back down to 900 rpms as it did before until the car has stopped moving? it never did this before:roll:

So i decided to clean the AIC, automatic idle control valve and it was dirty with oil, so i blasted it was brake cleaner and polished the body of it, it is from the Lucas system.

So i put it back on the car and now my idle is 1000 rpms i cant get it to go below that even when its really warm.

What did i do wrong? everything was fine before? should i oil the AIC as i put it back in bone dry.

I have to edit this, its 4.55 am and i have just taken the AIC out and opened it all up and gave it a proper clean this time and the little tip seems to be jammed?

i could'nt move it in or out? i even tried 2 volts 4 volts going up in 2 volts steps and nothing! i only got resistance in the first 2 pin holes of 57 ohms, i close the pipes and hooked it up to see if the wiring would move the plunger and nothing? should it be fully closed when the engine is runing and open when there is some load on the engine like from the alternator?

Is this normal for the plunger to be open all the time and not fully close the hole?

 

[Matthew]

A think a shot of light spray oil or WD40 would have been a good idea. Afterall, the AIC has moving parts. Dunno if the AIC should ever close completely.

It's common for idle to jump up high once crud has been cleared out of components in the inlet system, including the AIC. Over the years owners tweak up the idle as it drops due to debris. Take away that debris and suddenly the idle's too high.

On Bosch cars the way to adjust the idle speed is a bypass valve on the throttle body:

Lucas might be the same, I don't know. Wind the screw in to block the bypass port and slow the engine's idle speed. Be careful winding in the screw too far as it can damage the throttle body:

Also check that the throttle stop screw is properly adjusted (Bentley has instructions):

The slowly decreasing engine speed after 1500RPM might be to do with the throttle dashpot:

That damps the movement of the throttle when it's snapped shut. Again, instructions for adjustment are in Bentley (I can't remember what they are).

But then you may know all that already!

4.55am... do you ever sleep?! :lol:

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[mpribas]

Lucas has some electrical "help"...

Throttle control valve, I suppose....

 

[Fred]

This is a link to CU14 system wiring diagram. Its on the SAABMASTER site so url does change
http://townsendimports.com/Web/electrical_system_folder/Electrical_900_89-90/078-83.jpg
Your picture is of the throttle potentiometer.

 

[ShadowWorks]

I can't sleep when something is not right, i think am getting anal in my old age;oops:

Anyway the idle was still at 1000 rpms this morning and the car felt slow and my MPG has dropped alot!

So i took the AIC out again and this time i noticed the plunger has a metal tip and one side was very polished and the other side was not, i think by me removing all the gunk and goo! i have reduced the air tight sealing that the plunger should be doing and was doing before, so in this case cleaning the AIC was not the thing to do.

The Lucas system is a little different from the Bosch it would seem, there is no dashpot that stops the plate from snapping shut on mines?

Anyway i read that the stepping motor in the AIC moves the plunger backwards and forwards by some kind of throttle sensing? so I reved the engine and it moved, i now understand it cant be moved by hand.

The AIC shout be fully shut and air tight when the cars idles and when the idle has to pick up because of a load it should open a little, this is what happens with my AIC, cleaning it has picked up my Revs and i retro fitted some greeze to simulate the Gunk and guess what the idle was 800rpms and it sounded perfect and drove much better.

My greeze only lasted a few minutes before the idle went back to 1000 rpms.

The think i suspect now is the throttle stop screw, mines is wound down, right too the end and Matthews looks like it only half way down? am afriad to adjust this incase i mease up something else?

If i disconnect the battery for a few hours will this reset set the ECU or something? my brothers Honda requires this so it can remap itself, does the Saab Lucas system work like this as well?

 

[Fred]

You are going the right way, the collected experience of the forum is here:

http://www.saabcentral.com/techhelp/c900/idling_problems.php

As you say next step is to clean and set throttle opening.

 

[ShadowWorks]

Never do two things at once

I cleaned my throttle plate and AIC at once so i wasnt sure if it was the cleaning of the plate that moved the idle up or cleaning the AIC which moved the idle up, it was both really but mostly cleaning the throttle plate.

Matthew was right, the last owner must have never cleaned the throttle plate and just wound the screw down, cant think why as it seems silly to do that.

Cleaning the AIC is a good thing to do, i reset my throttle stop screw and and the idle is perfect again, lowered by 200rpms and feel and sounds so much better, it was not as big a deal as i thought and i was worried about nothing really!

 

[alan forsyth]

good to hear you got it sorted sha , will you be coming over this weekend ?

 

[silversaab96]

I've just had a not dissimilar prob with high idle on my 900, but due to another cause. As well as the idle being wonky, the engine speed drops suddenly by 100-200rpm whenever the fans cut in and put some load on the alternator. Turns out both vac hoses to the AIC are sucking in air due to being old and spongy, so it can't compensate for the load. Funny though..didn't think they'd draw too much current.

 

[cdaly]

Radiator fans are among the heaviest electrical power draws in the car (the rear-screen demister is another). As the fans get older, they'll draw more current, mainly due to bearings slowing down because of grease thickening. It might be possible to dismantle and clean the fan motors to restore their original power draw...

 

[silversaab96]

It might be possible to dismantle and clean the fan motors to restore their original power draw...

Thanks mate, I'll give that a shot soon, along with cleaning the AIC, which I didn't know you could do.... Got all the big stuff out of the way so doing all the little things is becoming very enjoyable. Too bad I'm selling it in a few months, but then I do have to make way for the '90 5-door turbo. :cheesy: