W126 500 SEC 1985 - Experiencing rough operation on cold start - Any suggestions?

[Geek2232]

After investing significant effort on preparing my SEC for the MOT, it has unexpectedly started experiencing severe performance issues upon starting.

The button initiates flawlessly and remains in a state of perfect idleness. Nevertheless, the engine fails to increase its revolutions and instead slows down, ultimately refusing to operate at full capacity. Once it has reached a higher temperature, the weather will become clear, but it is not optimal. After replacing the gasoline pump, filter, and lines, the vehicle initially functioned well. However, it has lately begun to have issues.

Do you have any suggestions about the first place to search?

[WiseSage]

Are you referring to the distributor cap and rotor arm? What is the age of the HT leads?

 

[bvlenci]

As these components age, it is normal for air leaks to occur at the injectors, inlet manifold rubbers, and other related parts.

E5E10 is not effective in improving the fuel system on Ke jet.

Does the engine exhibit a significantly elevated idle speed when it is cold?

[jennycarlotta]

These engines are susceptible to changes in vacuum pressure. Perform a smoke test on the automobile to detect any leaks. It seems that the problem persists when the temperature is warm, but is concealed by the warm environment. Most likely, the reason is that the ICV (Idle Control Valve) is closed, resulting in a reduced occurrence of hoover leaks.

[Matt865]

The distributor cap, rotor arm, and HT leads play a crucial role in the functioning of these vehicles.
Attempt to get a comprehensive collection of MB products if possible.
I had difficulties with a non-original distributor cap.
After replacing it with an authentic Mercedes-Benz part, my issues were resolved.

[bvlenci]

If the issue resolves within a time frame of 1-3 minutes, it is very probable that the cause lies in the cap and rotor arms. However, if it takes 15-20 minutes for the issue to clear up, it is more likely to be attributed to a vacuum leak or a sticky Idle Air Control (IAC) valve.

Regardless, if they are outdated and not impressive, then it is certainly worth making a change.

[Geek2232]

Thank you for all the responses.

The automobile has essentially remained inactive on the road for many years, but it was nevertheless started at least once every couple of months. Approximately a decade ago, the system was taken to a professional who conducted a thorough overhaul of the input system. This included performing a smoke test and replacing any seals, O rings, or gaskets that were deemed questionable. In addition, there were new leads and plugs installed. However, it is uncertain if the cap and arm were replaced.

Thus far, the operation of the device has consistently been flawless upon the act of turning the key.

The problem arises in cold weather, when the engine fails to start initially and stalls completely if you apply excessive power. However, after a period of 2-4 minutes, the issue resolves itself and the engine works smoothly. There are no issues with the idle; it remains precisely in the expected position.

Perhaps it would be worthwhile to consider replacing the cap and rotor.

[bvlenci]

If such is the situation, it is certainly advisable to replace the distributor cap and rotor arm.