Question about 1986 Mercedes-Benz 300

2 Answers

Cold start injector is not energizing. When i do get it started it runs rough until it gets warm.

Posted by on


2 Answers

  • Level 2:

    An expert who has achieved level 2 by getting 100 points


    An expert that got 10 achievements.


    An expert that got 5 achievements.

    Vice President:

    An expert whose answer got voted for 100 times.

  • Expert
  • 203 Answers

I am assuming this is an 86 300 e. first see if you are getting voltage to the cold start valve. this valve is fairly simple although it is hard to describe to someone how to test it and also there are other things that happen when these valves fail. assuming you do not have excessive cranking and you know that this valve is not working i'll just give you the most likley problem. on these earlier cis systems there was a 2 pole tempurature senser( 4 pole in the later version) on the in line six motor. if you look to the intake side of the engine it is the last senser located on the top of the head to the side of the valve cover. There will be 2 seperate wires going to the senser. both the cis and the idle speed computers use this senser. I would usually think the check engine light would be on but these earlier systems are not as sensitive. most likley the senser is giving false info to the cis unit which grounds that solonoid(cold start valve). take a ohm meter and test each pole form ground to the senser pin. compare the 2 readings. I know the 4 pole sensers cannot be more than 10 ohms differense. To make things easier on yourself just get a new senser and install it with a new crushwasher. ask for the pcm engine coolant temp. senser. The other sensers are used for your gauge and aux. fan.

Posted on May 17, 2009

  • Ryan Jasper
    Ryan Jasper May 25, 2009

    unfortunately in 86 $ 87 model years the cis computer did not have fault storing capabilities so it has to be failing at the time of code retrieval there are no hard faults


  • Level 3:

    An expert who has achieved level 3 by getting 1000 points


    An expert that got 20 achievements.


    An expert that got 10 achievements.


    An expert that got 5 achievements.

  • Mercedes-Benz Master
  • 19,396 Answers

You need to check all the factors that can affect cold start.

Check the AIF Sensor, check the air intake and the air filter. The air intake sensor can also affect cold start.

Also check your spark, and have a code reading done at your garage to scan car computer, this will tell more on the fault.

Posted on Mar 07, 2009

  • Ginko
    Ginko Mar 07, 2009

    If your car is a 1986 mercedes, things may be different if you have a carb model.
    In that case check primarily the idle settings and air settings on carb, the air intake and spark plugs.

    As you mentioned the injectors, I assume you have a diesel or an electronic injection model.
    In that case do an injector cleaning, replace air filter and spark plugs, if the problem persists check the AIF, check the air intake and the air filter. The air intake sensor can also affect cold start.
    Also do an injector cleaning, and test your fuel pump (test fuel pressure), fuel pump can also be cause for rough start.



1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

a 6ya Mechanic can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repair professionals here in the US.
click here to Talk to a Mechanic (only for users in the US for now) and get all the help you need.

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

2007 murano runs rough at cold start then runs fine

misfire can be from plugs and also from injectors. It it is fine when it warms up I would be looking at injector tip problems from the cold.

Jan 10, 2015 | 2007 Nissan Murano SL

3 Answers

Starts and runs fine.....rough runs, when you restart after warmed up

Sorry - I didn't see the vehicle information the first time.

Let me research this - i will get back to you soon.

Aug 03, 2014 | 1999 Subaru Legacy

1 Answer

Runs ruff while cold at start up

There is a door in your air intake that is thermoststicly controlled
that is to remain partially closed until tge engine warms up.Thereby letting in cold air on a cold engine, causing it to run rough.

Nov 08, 2013 | 1994 Dodge Spirit

1 Answer

I have a 95 Ford F350 with the 460 motor. It started running fine when cold but after it warms up it starts to run rough, lose power, and runs REAL rich. I'm only getting a little more than 2mpg.

It Sounds like it is staying in the "cold start" routine. It also sounds like the diagnostic computer is not working right, because it must be rich and the O2 is not telling you a thing.

I would start by looking for a temperature sensor. You may have 2, with 1 being for the dash and the other being for the engine controls. You want to replace the temperature sensor for the Engine controls. This will help get it out of "cold start" routine.

Change your thermostat. The onboard computer does not monitor operating temperature.

Fuel pressure regulator. Have pressure checked.It could be forcing too much gas in each time an injector opens.

If you can not do this yourself, tow it in. At 2 mpg it may be cheaper to tow it than to drive any distance for repair. The Mechanics are going to need some gas left over in it to work on the engine.

Also turn on ignition and energize the fuel pressure, check for leaking fuel lines. Put on fuelcap locks if fuel drops when parked.

For this much of an extreme problem, I would like to know what you find wrong with it. I hope my solutions help.

Sep 20, 2012 | 1995 Ford F350

1 Answer

2000 beetle cold start rough idle until it warms

Could be the fast idle sensor check to see that the vacume line is hooked up properly.

Mar 12, 2010 | 2000 Volkswagen Beetle

1 Answer

1998 Mercury Grand Marquis GS runs Rough when cold

I have the same problem and can
Not figure it out did u have any luck?

Feb 02, 2010 | 1998 Mercury Mystique

1 Answer

Engine runs rough on cold start warm ok

without more details about your truck it's hard to give you a reliable diagnosis. a common problem on a high mileage engine would be fuel injectors leaking fuel while the engine is off, causing a rough run until excess fuel is burned off

Dec 06, 2009 | Chevrolet Suburban 1500 Cars & Trucks

4 Answers

When car is cold it seemingly runs on 3 cylinders

seem like you got the same problem as my scion xa, check the fuel pressure regulater. bad regulater some time smell like leak gas. auto zone might cause you about $80.00.

Feb 09, 2009 | 1992 Honda Accord

2 Answers

Car trouble

Its because that the engine is very cold, try to worm it up more time before you start driving.

Jun 14, 2008 | 1999 Daewoo Lanos

Not finding what you are looking for?
Cars & Trucks Logo

Related Topics:

146 people viewed this question

Ask a Question

Usually answered in minutes!

Top Mercedes-Benz Experts

Colin Stickland
Colin Stickland

Level 3 Expert

22258 Answers


Level 3 Expert

77169 Answers

Michael Contreras
Michael Contreras

Level 2 Expert

166 Answers

Are you a Mercedes-Benz Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides