Mercedes-Benz Forum banner

1 - 3 of 3 Posts

·
Registered
1986 420 sel
Joined
·
43 Posts
Discussion Starter #1
Hello,

My car (1986 420 SEL) has been giving me problems for about a year now. I havent been driving it and havent been working on it allthat time. I sit on Benzworld and get a new theory and apply it but so far nothing has seemed to work. My daily driver is down and maybe will be for a while so now the choice is to walk or get to the bottom of this.
Here is the problem. I can start it up and it will idle fine and smooth, economy gauge pegged to the left and then it will move to the middle and run ruff. On the road, when I need power sometimes it will be there and sometimes not. The time it idles nice to nasty is not consistant. I was going to get a smoke test done on it but it am thinking if I had a vacuum leak it would be consistant. I replaced the temp sensor to the ECU and the O2 sensor thinking that those may have been sending it mixed messages. I replaced the vacuum modulator to the trans. I think I may have not have done that correctly so am going to redo it with a new one today hopefully. I can swap out ECU and Idle control relay and nothing changes. I have replaced all the vacuum lines and idle air hoses. It doesnt seem to matter if the system is in either closed or open loop. The last time it ran great is after I received a EZL ignition control from one of our fine members. It ran great for about two weeks and then this started to occur. So the question is (if it is the right question--there may be a better one) what happens when I shut off the engine that it will go back to good and then deteriate again? It has me baffled. Any help you can give would be greatly appreciated. Thanks Kim M.
 

·
Registered
1997 Mercedes-Benz S500
Joined
·
213 Posts
Hello,

My car (1986 420 SEL) has been giving me problems for about a year now. I havent been driving it and havent been working on it allthat time. I sit on Benzworld and get a new theory and apply it but so far nothing has seemed to work. My daily driver is down and maybe will be for a while so now the choice is to walk or get to the bottom of this.
Here is the problem. I can start it up and it will idle fine and smooth, economy gauge pegged to the left and then it will move to the middle and run ruff. On the road, when I need power sometimes it will be there and sometimes not. The time it idles nice to nasty is not consistant. I was going to get a smoke test done on it but it am thinking if I had a vacuum leak it would be consistant. I replaced the temp sensor to the ECU and the O2 sensor thinking that those may have been sending it mixed messages. I replaced the vacuum modulator to the trans. I think I may have not have done that correctly so am going to redo it with a new one today hopefully. I can swap out ECU and Idle control relay and nothing changes. I have replaced all the vacuum lines and idle air hoses. It doesnt seem to matter if the system is in either closed or open loop. The last time it ran great is after I received a EZL ignition control from one of our fine members. It ran great for about two weeks and then this started to occur. So the question is (if it is the right question--there may be a better one) what happens when I shut off the engine that it will go back to good and then deteriate again? It has me baffled. Any help you can give would be greatly appreciated. Thanks Kim M.
It sounds like a vacuume leak to me. It is a 24 year old car. If your idle is smooth and the car is in Park and when the car is warm, but still in park, your Fuel economy gauge goes to the middle that is a sign of a vacuum leak. Start with the stuff that you can easily change. Both rubbers to ICV, Breather hoses to every injector, on both sides with some new end caps at the ends, and a cross over pipe. I replaced mine. It looked great, but after a closer look i realized that all these pipes were either cracked or hard as a rock.
Remember, when it comes to the vacuum lines DO NOT cheap out. Only Genuene MB parts. I got a Uro cross over pipe, tried to save money, lasted me 3 days, then it just cracked. If your idle is not high and within the
700 RPMs in "Park" I dont think your idle control relay is at fault. Usualy when economy gauge moving in Park its a vacuum related. I changed the major vacuume lines it costed me no more than 120-150 bucks from
pelicanparts. com
 

·
Registered
1986 420 sel
Joined
·
43 Posts
Discussion Starter #3
found it

Today I was swapping out the EHA because I had a surging thing going on as well as all the other things mentioned above. I thought maybe the
EHA counldnt decide what to do or something like that. I was concerned with the less than perfect connection at the EHA. I went to test the wire to the ground post as it was the brown ground wire that I questioned. When going to the other end of the wire I found that the bolt on the post for the four ground wires closet to the EHA were loose. Ureka!!!!!!!! After months of poor running, testing components, swapping components, buying new components, scratching my head and wanting to cry, I tightened the bolt. I took it for a 10 mile test drive and it drove and performed like a brand new car. It seems was my problem all the time. How many hours did I spend on here digging and researching. Granted I know more but just goes to show stick with simple first. Thanks everyone for your imput. So glad to have my car back running like a Mercedes and pass someone again.
 
1 - 3 of 3 Posts
Top