Fast idle after war-up - PeachParts Mercedes-Benz Forum

Bill Mobley · #1 02-06-2007, 09:53 AM

I have a 1987 560SL. When I first start the car the engine RPM goes to 1,000. After a brief time the RPM drops to 500. I drive around the neighbor and stop several times. The RPM drops to 500 each time I stop. However, after the car temperture reaches normal operating range the RPM goes to 1,ooo and stays there. I recently replaced the cold start valve and some vacumn tips / lines. What could cause the RPM to go to 1000 after the car warms up? Thanks for any suggestions.

just-n-time · #2 02-06-2007, 10:23 PM

Quote:

Originally Posted by Bill Mobley

I have a 1987 560SL. When I first start the car the engine RPM goes to 1,000. After a brief time the RPM drops to 500. I drive around the neighbor and stop several times. The RPM drops to 500 each time I stop. However, after the car temperture reaches normal operating range the RPM goes to 1,ooo and stays there. I recently replaced the cold start valve and some vacumn tips / lines. What could cause the RPM to go to 1000 after the car warms up? Thanks for any suggestions.

Look into the Idle control valve and where it gets its signal.JNT

tjseitz2001 · #3 02-07-2007, 07:40 AM

I have an 89 560sel that is doing the same thing. I have been chasing it for a couple months now. Tom

david s poole · #4 02-07-2007, 09:33 AM

there is an idle control relay hidden behind the glove box with the fuel pump relay.you will need to remove glove box and panel underneath it to access but probably the problem.

david s poole · #5 02-07-2007, 09:35 AM

the relay for the sel is behind the angled panel on the floor where passengers feet go.

tjseitz2001 · #6 02-07-2007, 08:18 PM

David, Thanks for the tip. I will check it out and see if that helps.Do I dare ask what this relay looks like with out sounding too dumb? Thanks again Tom

tjseitz2001 · #7 02-07-2007, 09:29 PM

MTUpower, Thanks for the info. Sorry I didnt say I had the 89 560sel.So mine should be in the pass. foot well.... Yes I checked and cleand the ICV and rubber boots. I want to say when I unplug the ICV the idle goes UP from 1000rpm to say 13 or 1400rpm. Tom 89 560sel.

MTUpower · #8 02-07-2007, 09:56 PM

You can always check the throttle linkage. Remove the air cleaner and have a friend pump the gas pedal- you'll see the linkage moving. In the front there is a section that goes straight down. Take a 8 mm wrench and put it between the two linkages and twist- the lower one will then pop off- do the same to the bottom and then you have a short linkage section about 4 inches long. If you hold the end with pliers you can take the 8mm wrench and spin the lock nut down and then rotate the ball end. Making the whole section shorter will decrease the idle- making it longer will increase the idle. It only does so much- as the other controls will come into play. Idle is also a part of the fuel mixture. with the air cleaner off you can see the fuel distributor- which is what the air cleaner sits on. In the front of it is the mixture control- it's a 4.5mm allen wrench adjustment. Put the allen wrench into the hole and press down- it's spring loaded. By twisting either direction slowly you adjust fuel/air ratio I believe. This effects idle. So now you have about 5 different systems affecting idle. Oh- also is the warm up control- which is right next to the idle control valve. Tap on it a few times. It's designed to raise the idle just a bit when the engine is cold. While doing anthing tot he car be sure you know where you started with every change you make so you can set it back to where you started. YTou dont want to change a bunch of stuff and not be able to get back to the staring point- yo could really mess up how the engine runs and then you gotta spend alot of time or alot of $ to a pro to fix your F*&^up.

Shortness · #9 07-10-2007, 04:11 PM

Quote:

Originally Posted by MTUpower

The idle control box is next to the windshield washers, on the window side of the firewall, right on top- it's a black rectangular box that holds circuits inside.

Unable to find, can you clarify which winshield washer or do you mean wipers?

TIA

Wayne
'88 560sl Black