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  #1  
Old 2nd November 2005
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Default High idle

A few days ago I cleaned out the throttle body and also cleaned out the AMM with carb cleaner.

It now idles way too high. It also seems to get higher the longer it runs.

Its almost normal when it first starts up and then over time it will eventually get up to an estimated 1500-1800 rpm. (I say estimated because the tach does not work so I truthfully don't know, way to high though)

Does anybody have any ideas as to why cleaning the throttle body, which was rather gunked up, or cleaning the AMM would cause the idle to suddenly jump so high?

I suppose I could have messed the AMM up somehow. I don't think so though, it was just carb cleaner, I was just trying to clean off the temp sensor in there.

It idles high enough that I really dont feel comforatable driving it, it diesels when I shut it off and thats not good for an engine. I've taken to loading it with the clutch right as I shut if off so that it pulls the rpm's down before I kill the engine. That works pretty well but I"m going to be getting some horrible gas mileage if I sit in traffic idleing at 1500-1800 rpm.

An ideas would be welcome, I'm a bit puzzled. Its probably just some simple thing I overlooked or left unfastened.
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  #2  
Old 2nd November 2005
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The creeping warm idle usually indicates lean running behavior which means a leak in the intake tract. It can also mean the throttle plate is just too far open.

It doesn't seem likely that you ruined the AMM. I have cleaned the AMM on my car the same way with no ill effects.

It is possible that in cleaning you have cleared the idle circuit/bypass allowing more air. Typically the idle control valve can handle a small change like that.

When is the last time the idle bypass, the throttle stop screw and the position switches/sensors were adjusted ?
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  #3  
Old 3rd November 2005
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Considering the rising idle and dieseling, I'd say the engine's running rich. Sounds like it's not coming off the cold-start fuel enrichment cycle.

NTC sensor?
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  #4  
Old 4th November 2005
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Matt,


If the car is one of your 1988 non-turbo models, try reading out trouble codes even if your check-engine light is not on (some problems do not trigger the CEL).

Also, check your TPS (throttle position sensor) to make sure it clicks when you close the throttle. If not, you can adjust it.
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Old 5th November 2005
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Quote:
If the car is one of your 1988 non-turbo models, try reading out trouble codes even if your check-engine light is not on (some problems do not trigger the CEL).

Also, check your TPS (throttle position sensor) to make sure it clicks when you close the throttle. If not, you can adjust it.
Its the 1987 900S. I've already checked the tps, swapped out the NTC sensor, AMM, and IAC with ones from my other cars (with the right part #'s of course ). Didn't change a thing.

It happened right after cleaning the AMM and throttle body, and since I tried the AMM from my turbo on it and it didn't change anything, I can only assume it is somehow related to me cleaning the throttle body. The rps's also drop very slowly, almost as if the dashpot was adjusted to far in or something, but its not.

It was having cold starting problems beforehand and that is why I was messing around cleaning things. The starter quit on me the other day too, I haven't had time to change that so I haven't been driving it.

I've pulled codes out of the 88's many times but never on a 87. Is it the same procedure but just a different location for the connection? Under the back seat right?

There is still a connector at the right front fender but if I recall right, grounding that out on an 87 will fry things.
Cheers
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  #6  
Old 5th November 2005
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This might be really simple - as the throttle-body became gunked up, the idle speed lowered and this was adjusted up manually to compensate. Then you clear out all the gunk, and we're back to true idle speed.

You have tried adjusting the idle speed down?
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Old 5th November 2005
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Quote:

This might be really simple - as the throttle-body became gunked up, the idle speed lowered and this was adjusted up manually to compensate. Then you clear out all the gunk, and we're back to true idle speed.

You have tried adjusting the idle speed down?
I thought of this, and I'm wondering if someone came up with a really creative way to increase the idle because since its an 87 16 valve I don't think there is really any way to adjust the idle, its supposed to do that automatically.

I did check the throttle stop and dashpot to make sure they weren't adjusted to far out and keeping it from closeing all the way, no problems there.
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Old 5th November 2005
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Doesn' the throttle body have an adjustment screw like this:


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Old 5th November 2005
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No I'm afraid not. I wish it was that easy, but on the 16 valve systems its supposed to adjust itself automatically. So they took away that little adjustment screw to keep people like me from just adjusting out something that should have been tracked down and fixed properly. Technololgy.
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Old 5th November 2005
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The throttle body shown in the pictures is from my old 1988 T16...
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Old 5th November 2005
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Interesting. Must be one of those UK vs. US market idiosyncrasies.

My 87 16V, 88 16V, and 88 16V Turbo do not have it. I've only seen it on the older 8 v models.

Does yours have the Bosch or Lucus system?
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  #12  
Old 5th November 2005
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Do you have the Lucas system?

I cleaned the idle control valve and throttle plate and got a high idle of 1200 rpms, i got worried, Matthew stated that owners some times turn the idle up to pick the lagging rmps up, its like a lazy fix.

I had to reset the idle screw which is a small 3mm screw with a hex bolt holding it's position.
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  #13  
Old 5th November 2005
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Quote:
Originally Posted by Matt88S
Does yours have the Bosch or Lucus system?
Bosch LH2.2.

Sha - where was that idle adjustment screw? Doesn't sound similar to the one in the pics so perhaps there's something else that Matt could look for.
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  #14  
Old 5th November 2005
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In post number 8, in the very first picture.

Too the left of the spring, at the bottom left hand side of the picture is a small threaded shaft with a striaght slot on top held it in place by a 8mm nut, thats the screw i used to adjust the idle.

The hex bolt above the spring next to the 2 blue silicone hose i left well alone.

The US Saabs dont have the top hex bolt for some reason.
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  #15  
Old 5th November 2005
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Quote:
Originally Posted by ShadowWorks
Too the left of the spring, at the bottom left hand side of the picture is a small threaded shaft with a striaght slot on top held it in place by a 8mm nut
That's the throttle-stop adjustment screw. Bentley says IIRC that you should adjust it so that it's *just* touching the throttle cam, and back it off 3/4 turn.

Quote:
Originally Posted by ShadowWorks
The hex bolt above the spring next to the 2 blue silicone hose
That actually is the idle adjustment screw.

At the top of the throttle body there's an airway that bypasses the throttle plate. The screw restricts the airway to allow a certain amount of air past the throttle when at idle.

High idle problems can be a combination of things: vacuum leaks, mis-adjusted TPS, mis-adjusted throttle stop and mis-adjusted idle adjuster. I've found that it's sometimes easier to reset all those instead of trying just one.
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Old 5th November 2005
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Mine is bosch as well, what can you say but that was saabs way. Mix and match.

Quote:
Too the left of the spring, at the bottom left hand side of the picture is a small threaded shaft with a striaght slot on top held it in place by a 8mm nut, thats the screw i used to adjust the idle.
Do you mean the throttle stop?

I've already checked that. Its only about a turn in, not enought to effect idle.
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  #17  
Old 5th November 2005
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If the throttle-stop is screwed in to touch the throttle cam, and then one turn more then that might be enough to affect idle. A comparatively small movement on the throttle cam at that position might would open the plate enough to allow a significant amount of air to pass.

The screw shouldn't be touching the cam wen the throttle's shut.

Gotta be worth another look.
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Last edited by Matthew; 10th January 2006 at 05:19 AM. Reason: Typo
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  #18  
Old 5th November 2005
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My throttle stop screw used to be in touch with the throttle cam, after cleaning the AIC and throttle plate the idle jumped up.

I didnt know that the true idle adjustment was the top bolt, Well i do LSNED

I was told that you should be able to slide or pull a 0.06? feeler gauge past the throttle plate? this is how you know if the plate is in the right position.
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  #19  
Old 6th November 2005
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Quote:
Originally Posted by Matt88S
Its the 1987 900S. I've pulled codes out of the 88's many times but never on a 87. Is it the same procedure but just a different location for the connection? Under the back seat right?
Unfortunately, the '87 has the LH 2.2 system, from which you can't pull codes

I suggest looking in the Bentley manual; there's a section on setting up base idle for the 2.2 system step by step (pages 240-24 to 240-27).

Maybe adjusting the TPS (throttle position switch) might be all you need, but do the entire procedure just for peace of mind
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  #20  
Old 8th November 2005
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Oh i checked today and my UK 91-900c does not have that adjustment screw, only the smaller throttle cable screw, so its not a US UK thing, post 1990 900 in the UK switch to Lucas for some reason.

Matthew your silicone vacuum hoses look chunky, whats the ID of them?
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