How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Marty Your Own Question
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 54019
Experience:  Bosch Certified Master Tech. Over 35 years experience.
Type Your Mercedes Question Here...
Marty is online now
A new question is answered every 9 seconds

I have a 1981 Mercedes 380SL. Car starts first time, idles

Customer Question

I have a 1981 Mercedes 380SL. Car starts first time, idles ok most of the time, but when I put it in gear it "lopes"( shakes ) quite considerably. What is really confusing is that it accelerates well (no misses, or hesitation) and runs pretty smooth (like normal) when driving. Problem is when I stop at a traffic light the car starts to lope again, and shakes so much I have to put it into neutral until the light changes and I can give it some gas.
I have owned the car for almost 6 years and this issue just started recently. I have had it serviced with a tune up but it did not solve the problem. Any and all ideas welcome.
Submitted: 1 year ago.
Category: Mercedes
Expert:  Marty replied 1 year ago.

Hi, my name is*****'m assuming that the engine tune was done properly and that the overall ignition system is in good order. If the car runs smooth off idle but shakes and runs rough at idle I'd have the fuel mixture checked and have the intake system checked for vacuum leaks. Rough running at idle is typically caused by incorrect fuel mixture or vacuum leaks at the manifold or around the injectors or by a fault with the fuel distributor or the injectors.

Let me know if you have any questions.


Customer: replied 1 year ago.
Sir, I realize that there are a number of potential areas where there can be a problem, and checking all the areas of concern in your answer will probably resolve that problem, but your answer is a little too vague for me. I am not a mechanic and was hoping instead of an overall generalization of the many potential possibilities, that you could drill down and identify areas that a layman such as myself could focus on in some kind of chronological order. What and where would you start your process of elimination, how would I check the fuel mixture, any particular vacuum lines I should start with, etc.
Expert:  Marty replied 1 year ago.

I can explain this much easier if we talk on the phone.

Customer: replied 1 year ago.
Sir, I don't really see the advantage for me to pay a further $18 to have a phone conversation. Your generic answer was ok but it contained mostly what I had already suspected ; fuel mixture, vacuum lines, etc. What I was expecting was a little more detail on where would you start the process of elimination. I'm sure if you were doing the work, you would determine a start point and work methodically thru a logically process.
Expert:  Marty replied 1 year ago.

No problem on the phone call. That's entirely up to you but I can give you a whole lot more information in a phone conversation. I could write you a book on all of the things you need to check. If you want a starting point I would buy a can of carb spray and spray around the injectors and manifold with the engine idling and see if it affects the engine running. Vacuum leaks at the injector seals are a common problem. You can evaluate the mixture by pressing down 1 mm on the air flow sensor plate and see if it improves the engine idle. If the idle stalls try lifting up 1 mm on the plate to see if the rpm improves. If the engine running improves when you press down it tells you that the mixture is too lean. If it improves when you lift up it means that the mixture is too rich.

Let me know if you have any questions. Please remember to click on a rating for my service.