Idling problems
Thread Starter
Newbie
Joined: May 2010
Posts: 7
Likes: 0
1987 420 SEL
Idling problems
My Mercedes 420 Sel has an idling problem when I first start it, it idles really low almost to the point of turning off after reeving it up it clears out then idles high and when I put it in gear it seems to pick up more then slam tranny drop into gear.. Dose anyone have any ideas? .. Please help. Thank You.
Last edited by dannymiro; Jun 12, 2010 at 03:40 AM. Reason: misspelling
MBWorld Fanatic!
Joined: Jan 2007
Posts: 1,152
Likes: 29
From: Sydney, Australia
190D 2.5 (x2), 190E 2.6, W202 C240,W202 C43 (C55), W210 E55, W212 E250CDI
Check the fuse in the overvoltage relay (OVP relay). It may be blown. Also get a digital multimeter and check the dwell between terminal 3 in the diagnostic plug and earth. It should oscilate. If it is a fixed value then the engine control unit may not be working (faulty OVP relay) which is causing an uncontrolled idle among other things. Other symptoms include slow to start start cold and higher fuel consumption, possible ABS light on dash.
Newbie
Joined: Jun 2010
Posts: 1
Likes: 0
laurastone
I meet the same problem, too. Thanks Ausmbtech, thanks so much for your answer.
__________________
herman miller aeron chair
__________________
herman miller aeron chair
Thread Starter
Newbie
Joined: May 2010
Posts: 7
Likes: 0
1987 420 SEL
The over-voltage relay fuse is good there is no ABS light on the car dose have a slight misfire like put put put. I have a digital multimeter and checked the service plug on the left fender with the round plug and set the meter at V 20 and there is no movement. Is this the right service plug? and setting for the meter ? The manual I have showed a diagnostic plug on the right fender towards the back but my car did not have one there and this is the only one I found.
MBWorld Fanatic!
Joined: Jan 2007
Posts: 1,152
Likes: 29
From: Sydney, Australia
190D 2.5 (x2), 190E 2.6, W202 C240,W202 C43 (C55), W210 E55, W212 E250CDI
The over-voltage relay fuse is good there is no ABS light on the car dose have a slight misfire like put put put. I have a digital multimeter and checked the service plug on the left fender with the round plug and set the meter at V 20 and there is no movement. Is this the right service plug? and setting for the meter ? The manual I have showed a diagnostic plug on the right fender towards the back but my car did not have one there and this is the only one I found.
Trending Topics
Senior Member
Joined: Oct 2004
Posts: 272
Likes: 3
From: Michigan
SL600 r230, SL600 r129, SL500 r230, ML320, C280 Sport, R170 450SL, 190e 2.3 16V (2)
To test OVP = pull it out of its socket with engine running - idle should jump way up.
To test ISC = pull it out of its socket - idle speed should jump way up
To test ICV = pull the connector off, idle speed should jump way up.
If you do all three of those, and you get the desired results as stated, then they are <probably> not bad.
Next check all your air tubing for leaks. You can do this with a smoke generator or with Gumout Carb Cleaner. With engine running and warm, spray gumout or blow smoke around all the rubber air hoses. With the gumout, the engine will stumble when you find a leak; with smoke, you'll see the smoke sucked in at the leak.
You have two hoses running parallel to the valve cover, one going across under the fuel distributor, and then the short hoses at the ICV.
There are also "donuts" below the intake manifold. If those are leaking, you have a bit bigger of a job at hand, but it is not difficult, just time consuming.
If none of these find any issues, then you have to check your coolant temperature compensator switch (B11 switch):
B11/2 CTS
Temp C -- K Ohms
20C -2.5K
30c - 1.7k
40c - 1.18k
50c - .84k
60c - .60k
70c - .435k
80c - .325k
But I bet you find the problem when you get to the air distribution hoses.
To test ISC = pull it out of its socket - idle speed should jump way up
To test ICV = pull the connector off, idle speed should jump way up.
If you do all three of those, and you get the desired results as stated, then they are <probably> not bad.
Next check all your air tubing for leaks. You can do this with a smoke generator or with Gumout Carb Cleaner. With engine running and warm, spray gumout or blow smoke around all the rubber air hoses. With the gumout, the engine will stumble when you find a leak; with smoke, you'll see the smoke sucked in at the leak.
You have two hoses running parallel to the valve cover, one going across under the fuel distributor, and then the short hoses at the ICV.
There are also "donuts" below the intake manifold. If those are leaking, you have a bit bigger of a job at hand, but it is not difficult, just time consuming.
If none of these find any issues, then you have to check your coolant temperature compensator switch (B11 switch):
B11/2 CTS
Temp C -- K Ohms
20C -2.5K
30c - 1.7k
40c - 1.18k
50c - .84k
60c - .60k
70c - .435k
80c - .325k
But I bet you find the problem when you get to the air distribution hoses.
MB World Stories
The Best of Mercedes & AMG
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
10 Most Reliable Mercedes-Benz Models You Can Buy Used
Verdad Gallardo
MBWorld Fanatic!
Joined: Sep 2005
Posts: 6,189
Likes: 242
From: Albuquerque
'10 CL550, '12 GL550
When your engine starts cold, temp sensor advises computer to
- activate the cold start injector to provide more fuel
- activate the idle control valve to provide more air to create faster idle
You can probably imagine the problem if one or the other doesn't happen. Since you need the richer mixture when cold, you can imagine that a vacuum leak would interfere.
- activate the cold start injector to provide more fuel
- activate the idle control valve to provide more air to create faster idle
You can probably imagine the problem if one or the other doesn't happen. Since you need the richer mixture when cold, you can imagine that a vacuum leak would interfere.
Member
Joined: Dec 2008
Posts: 143
Likes: 6
From: N. Virginia
2023 E 53 sedan
What is the normal idling speed, anyway? I remember the SLK 320 I used to have idles around 750 rpm with or without the AC. MY CLK 500's idling speed over the past 3 weeks has gone up to around 850 rpm with the AC on which I noticed is kinda high cause just releasing the brakes when in gear the car starts moving without having to step on the gas. Idle goes down to 750 when I turn the AC off. Yesterday, I noticed with the AC on it was at 750 then it goes up to around 850 again after a few minutes. Same thing happened again today. Could my car be having the same problem(s)?
Thanks in advance,
Al
Thanks in advance,
Al
