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Discussion Starter #1
Ok I have gone through most of the checklists in the manual and so far haven't been able to find the problem. Maybe somebody here has some guidance based on my situation. My idle is normal cold, high warm (1250rpm) AC off, 1100rpm AC on, Idle is also normal in gear.

OVP (Overvoltage Protection Relay)
checks out ok per manual, power present fuse not blown.

Coolant temperature sensor
car idles normally when cold, high idle only when warmed up, sensor ok.

Ignition control unit
no checks given in manual but car runs fine so I am assuming this is not the
problem.

Throttle valve switch
Resistance checked out, I did notice that with the accelerator pressed to
the floor and kickdown switch engaged I had to push the linkage further to
get the ohms to zero. I'm sure this doesn't affect my idle but could I be
losing some HP at full throttle???

Electronic speedometer
no checks given, my speedo works.

Starter lockout and backup light switch
did not check

AC compressor control unit
did not check but seems to be functioning correctly rpm drops about
150 rpm with AC on.

Idle speed air valve
Current at idle speed 1050ma
resistance 4.5 ohms
wiring checks ok
I did take this out and clean it, and it operates, if I unplug it revs go up
I also tested it with a 9v battery and it seems to close fine, could this be
working but not working fully?

Idle speed control unit
I disconnected it and did the checks on the harness, I did not do the
checks in section 5.0 under TF signal for N16/4.
I tried shaking, twisting, banging it and idle speed was not affected.

Air pump
Mine doesn't seem to be working, does this have much affect on idle?

Sensor plate
I read 073-245 and mine doesn't seem to be as it should. There is
a few mm of free play, I don't hear an "audible impact on the spring loaded
stop when it returns from full open. Also if I manually pull it up when the
car is running the idle speed comes down.
The zero position also seems to be low compared to the pictures in the
manual. Should I mess with this or is the problem elsewhere?

The only thing I didn't check is vacuum, will the car idle normally with the air cleaner removed? If so the loose breather hose from the passenger side valve cover is not an issue. My vacuum lines look to be in good condition the hoses are not cracked and the rubber ends are still soft and tight on the fittings.

Any advice would be greatly appreciated.
 

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It could be the idle air valve. There should be a voltage value to test for. I think(IIRC) if you apply 12V(VERY BRIEFLY) to the valve the engine should stall.

Also, you might have a vacuum leak. Use carb cleaner or something like that. Spray it around any potential vacuum leak, also try to get under the upper intake manifold. Where is the economy gauge needle at idle?
 

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The idle speed control unit - is that the little black box under/around your steering column?

If so, did you pull it apart and have a look inside?

I had the same problem as you're having, and when I pulled the box apart, the internals were burnt. Replaced it with a spare one I had lying around, and the idle was back to normal.

Lucky I had a spare one, as a new unit is serious $$ - even a used one doesn't come cheap.. at least not here in AUS anyway.

Good luck!


Cheers :cool:
 

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PAS--

I'd say it's an idle control unit (under the passenger footwell). I have a few spares, and in testing one of them, I had the exact same symptoms (normal cold, high warm). I can send you one of my spares and a spare ICV (once I test them all) if you want-- They cost me less than $10 each at the JY.

Dave
 

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I paid $14,000 + freight for my '86 560, and $16,400 + freight for my '88 560 - and that's AUS $$ too! Granted they are both Euros w/ Tri-ys, but still...

Those Americans don't know how lucky they are!


Cheers :cool:
 

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Discussion Starter #9
It could be the idle air valve. There should be a voltage value to test for. I think(IIRC) if you apply 12V(VERY BRIEFLY) to the valve the engine should stall.

Also, you might have a vacuum leak. Use carb cleaner or something like that. Spray it around any potential vacuum leak, also try to get under the upper intake manifold. Where is the economy gauge needle at idle?
I checked the idle speed air valve per the manual and it checked out ok, it is doing something because when I disconnect it with the engine running the revs go up to 1800 - 2000 rpm. I will try putting 12v to it and see what happens.

Are there any typical locations that are good to start with for vacuum leaks? The thing is that the car idles well in gear and when cold so I don't think I have any serious leaks. The economy gauge is pegged low at idle.
 

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Discussion Starter #10
PAS--

I'd say it's an idle control unit (under the passenger footwell). I have a few spares, and in testing one of them, I had the exact same symptoms (normal cold, high warm). I can send you one of my spares and a spare ICV (once I test them all) if you want-- They cost me less than $10 each at the JY.

Dave
Dave thanks for the offer I sent you a pm.
 

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If all else is OK it will be the rubber donuts / sleeves on the intake manifold (8 pcs.)
this rubber becomes brittle and deforms just enough to cause vacuum leakage. need to remove upper manifold to thoroghly inspect.
 

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Thanks, these threads aren't very exciting, but they are informative.
 

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Discussion Starter #14
I like to follow up with the solution, a lot of times you find threads that have the info you are looking for but after they solve the problem most people never come back to the thread to tell what it was. You look at 10 threads and none have the answer.
 

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By under the passenger footwell, do you mind under the carpet, or behind the glove box? i suspect it's behind the glove box, and in this case, do you have to take the glove box down as well as all the plastic tubes? Sorry about that, I'm struggling to find it. Would anyone have pix?
Thanks!
 

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nrapp--

The ICU is in two different places, depending on the year of the car. The later gen 2s have it behind a false wall underneath the carpet in the passenger footwell-- no need to drop the glove box or anything-- simply pull the carpet and remove the plastic cover. Earlier cars had the ICU between the two firewalls in the engine compartment. What year is your car? That would help in getting you better instructions.

Dave
 

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NP, nrapp--

On a w107, I haven't a clue where the ICU is. Maybe someone here does, but you might have more luck on details like this in the w107 forum...

D
 

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ElRojo,
Thanks for your help. Checked this morning, but there's nothing under footwell. Posted a message on the 107 forum.
 

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High idle on 1989 e260

Hi - I have a similar, though more extreme problem. My e260 idles at about 3000rpm after about a minute's warmup. When I turn the steering wheel to full lock in either direction, it drops to about 2000. It started doing this after having the opposite problem - low idle and stalling - for a day. Then this high idle, but on two occasions it has started and run completely normally. So I am guessing some kind of sensor is going wrong, but does anyone know how to identify what this might be? I see a lot of talk about the MAF sensor ... but I don't seem to have one - is this something that is only in cars with fuel injection? I have an air filter and carb etc.

thanks for any help -

Andrew
 
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