1985 500SEL Starts great but idles around 1100-1500 RPM (used to idle about 800) Some times it's about 800 and some times it is arround 2000 nut it is usually between 1100-1500 and I can't pin down any sort of pattern. I am not sure if this is a related issue or not but the Economy gague on the dash is always in the red evev when idleing near 800. any ideas? I did not buy this car to save gas but with gas prices the way they are I can aford for it to be burning more gas then it is suposed to.

You have a vacuum leak or a leak of the piping which comprises the idle air system. It could also be an idle air control valve stuck open. Your car should idle at 650± 50 or thereabouts. Even 800 is a little high. Get it looked at soon since slamming the car into gear at 1100-2000 RPM will land up costing you much more in transmission repairs than correcting this relatively minor issue.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Thanks for the quick reply,

I love to work on this car myself, do you have any advise or have you seea thread that will help me check this out? I saw an article in DIY that describes how to check for leaks in the vaccum system. Does this apply to my issue.

Thanks

the air cleaner and with the engine running spray wd40 on all the vac lines. when you are near the leak the engine will speed up.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

That sounds simple enough, I will give it try tomorrow morning and see what I can find. I guess the fix is to just replace the leaking line?

the rubber fitting.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I found the leak! That was easy enough. One of the thermo-vacuum valves has broken. I noticed corrosion around these valves, I think there are three of them, green and rusty looking kind of like battery terminal corrosion. I think these are Thermo-Vacuum valves. They are not expensive but are they hard to replace and is there anything I should know about this job before I get started?

i had high idle on my 420sel. there were 2 problems. vacuum leaks and idle air valve. its easy to change vacuum lines just pull them off and replace. to check idle air valve i took one rubber hose off made a plug with about 5mm diameter opening in it and stuffed the plug into hose and reinstalled the hose back on idle air valve. idle became normal 650rpm. then i just replaced idle air valve with junk yard one and no problems ever since. about economy gauge. maybe that is your vacuum leak. if its always in red chances are its not connected or vacuum hose to it is broken. hope this helps and good luck

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1999 ML430 Silver 135k ml
Smoked LED taillights, Alpine in-dash DVD player, 12" sub, Pioneer components, 2 amps, 4200k HIDs, ML55 headlights, 20" rims, mirror LED blinkers

SOLD. 1996 E320 145k ml. Burgundy

SOLD but miss it everyday 1992 500sel Black
Chime buzzer mod,Alpine CD/MP3 player with stock amp,Euro headlights,S600 grill,20" rims, BEST CAR EVER!

SOLD. 1990 300E White
187k ml,smoked tails,Euro headlights,17rims,Intake,12" sub in first aid kit,alarm/autostart,buzzer mod

be replacing the thermo-vaccum valves on Saturday so that will fix the vaccum leak, if that doesn't solve the problem I will move to the idle air valve and follow the steps you laid out. I'm not too worried about the economy gauge as long as I know it is broken, if it is accurate I am using WAY too much gas.

Thanks to all for your help on this.

Well I replaced the thermo-vacuum valves that were leaking and that did not fix the idle or the economy gauge. I continued with the WD-40 leak test as mentioned above but I have not found any more vacuum leaks.

I did do something that may have been quite stupid of me. I stuck my handy dandy allen wrench into the mixture adjustment tower and gave it a few turns. I did not count how many or pay attention to what direction I was turning it. I mainly wanted to see if would have any effect on the idle, the engine was running while I did this. I turned the car off after I did not notice any effect on the idle and now it will not start, any advice?

is to try to put it back the way it was.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

It's actually a little tricky to even engage the allen screw, so unless you had a voltmeter hooked up and watched the reading change you didn't change anything.

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Davo

500sl R107