Rough idle and hesitation

1985 MERCEDES BENZ 380SL

1,000 MILES • 5.5L • V8 • 2WD • AUTOMATIC

SRF770

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Hi, I just rebuilt the fuel distributor and it starts up now, which is great. However, when the engine is running and I press the gas pedal, there is a significant hesitation and the car almost stalls. A few things to note:

There is about 1" gap in the air flow plate when the engine is off or idling. Every picture I've seen shows the air plate with little or no gap, so I'm not sure if this is the cause. I suspect the previous owner messed around with the plate. What is the optimal gap?

Would this be a result of the air/fuel mixture? I've tried to adjust this but the allen wrench seems to turn too easily in the fuel mixture chamber, so I'm not sure I'm actually adjusting anything.

Anything else I should consider checking?

Thanks in advance.

Aug 24, 2020 at 10:22 AM

JACOBANDNICKOLAS

CERTIFIED EXPERT
110,175 POSTS

Hi,

Please understand, because of the model year, my technical info is somewhat limited. However, lets give this a try.

When you say the air flow gap, are you referring to the throttle plate? If so, it shouldn't be open that far at idle. Here are the directions for adjustment:
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1985 Mercedes Benz 380SL (107.045) V8-3.8L (116.960)
Throttle Plate
Vehicle Power-train Management Fuel Delivery and Air Induction Throttle Body Adjustments Throttle Plate
THROTTLE PLATE
NOTE: The throttle stop screw is not used to adjust idle speed, it is used primarily to keep the throttle plate from sticking in its bore. Adjust only if the setting has been tampered with and is suspected of improper adjustment.
1. Use a screwdriver to back off the throttle stop screw (you may need to loosen a locking nut) until there is clearance between the screw and the throttle valve lever.
2. Use a small piece of paper as a feeler gauge and adjust the screw until it lightly contacts the paper.
3. From this position, turn the screw in 1/2 turn, and lock it down.

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Next, if that doesn't help, have you confirmed there are no engine vacuum leaks? If not, do that next. Here is a link showing how that is done:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

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Let me know if this helps or if you have other questions.

Joe

Aug 24, 2020 at 7:43 PM