1986 500SEL Engine Tuning/Idle Troubles! Any and all help will be much appreciated!
04-24-2012, 10:57 PM
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1986 Mercedes Benz W126 500SEL, 1976 Buick Electra Limited Park Avenue
1986 500SEL Engine Tuning/Idle Troubles! Any and all help will be much appreciated!
I am new to this forum and own a 1986 W126 500SEL, i love the car and has always been a fairly reliable source of transportation however recently it has become a pain.
The car was being used daily for about two weeks and one day it began missing terrribly. I knew immediately that it would be the number two cylinder spark plug having fouled or shorted as this has happened twice or thrice in the past. The valve guides are weak and are allowing some oil to enter that chamber.
Typically a quick plug change would sort everything out and the car would be running normally.
However this time after the plug was replaced (it was bad and all others were checked they are fine) the car continued to have problems.
The idle was very rough and it would surge as though the car is struggling not to stall. However at any rpm above idle in any gear the car was perfectly fine. We tried adjusting the mixture but that was to no avail.
Finally the idle control valve was removed and cleaned out using some WD40 and was blown into (by mouth not compressed air) and allowed to dry before being reinstalled.
This seemed to fix the problem and the car ran beautifully for some a few mins on idle till hot and then a good 2 to 3 km drive. However suddenly the problem resurfaced accept now it was much worse than before.
The car would stall immediately after firing up and it was very difficult to get the rpm up enough to keep it running. However once that was done to drive the car home, above about 2000rpm again the car drove fine but when left to idle it stalled immediately.
As a result i assumed the Idle Control Valve needed to be replaced so i purchased a brand new VDO unit using their online catalogue ie. Part Number - "Siemens/VDO 408202010002Z."
I installed the new part, made sure all the hoses were hooked up and the car fired immediatly and settled to a very smooth idle when cold. However as the car heated up it began to surge and splutter once again and seemed to struggle to stay at idle. When i tried to give it some gas in this condition to see if it would clear up the engine reacted very poorly and continued to seem to be choking severly and even gave off quite a large back fire.
I need help diagnosing what is wrong with the car and have gone into this much detail so that you guys have a clear idea of what the car is doing and what has been done to it. I do apologize for the long rant but i am getting a bit desperate and veru frustrated.
Any help will be much much MUCH appreciated!
And i thank you in advance
Taimur
The car was being used daily for about two weeks and one day it began missing terrribly. I knew immediately that it would be the number two cylinder spark plug having fouled or shorted as this has happened twice or thrice in the past. The valve guides are weak and are allowing some oil to enter that chamber.
Typically a quick plug change would sort everything out and the car would be running normally.
However this time after the plug was replaced (it was bad and all others were checked they are fine) the car continued to have problems.
The idle was very rough and it would surge as though the car is struggling not to stall. However at any rpm above idle in any gear the car was perfectly fine. We tried adjusting the mixture but that was to no avail.
Finally the idle control valve was removed and cleaned out using some WD40 and was blown into (by mouth not compressed air) and allowed to dry before being reinstalled.
This seemed to fix the problem and the car ran beautifully for some a few mins on idle till hot and then a good 2 to 3 km drive. However suddenly the problem resurfaced accept now it was much worse than before.
The car would stall immediately after firing up and it was very difficult to get the rpm up enough to keep it running. However once that was done to drive the car home, above about 2000rpm again the car drove fine but when left to idle it stalled immediately.
As a result i assumed the Idle Control Valve needed to be replaced so i purchased a brand new VDO unit using their online catalogue ie. Part Number - "Siemens/VDO 408202010002Z."
I installed the new part, made sure all the hoses were hooked up and the car fired immediatly and settled to a very smooth idle when cold. However as the car heated up it began to surge and splutter once again and seemed to struggle to stay at idle. When i tried to give it some gas in this condition to see if it would clear up the engine reacted very poorly and continued to seem to be choking severly and even gave off quite a large back fire.
I need help diagnosing what is wrong with the car and have gone into this much detail so that you guys have a clear idea of what the car is doing and what has been done to it. I do apologize for the long rant but i am getting a bit desperate and veru frustrated.
Any help will be much much MUCH appreciated!
And i thank you in advance
Taimur
