1991 300SL HEsitation
 

Hello all,

I am having a hesitation problem with my 1990 300SL (CIS fuel injection). Here are the details.. what should I look at next???

Problem:
-Hesitation when accelerating from idle.
-No problems with starting engine, idling, or once car has started moving. Accelerating from 5mph-60mph is perfectly fine!
-Anything other than light pedal pressure causes it to bog down for a second before it accelerates. Hard acceleration causes it to stall!

Conditions:
-Happens consistently all the time (cold weather, just after starting, when fully warmed up, etc, etc.)

Thanks

Tom

Throttle Responce
 

First thing i would do is have your Throttle cleaned if you haven't already. Buy Throttle (Not Carb!!!) cleaner and spray into the throttle to dissolve grease/ grime that has built up and could be causing the throttle plate to stick on initial accelleration.

Second, I would check your Coolant Temp Sensor. It is located on the top of your water pump. I was experiencing the same problem with my M104 engine and it looks like it was the coolant temp sensor after all.

Between those 2 updates, you should be ok.

Be aware, in a very rare circumstance, it could be early signs of a failing ETA (electronic throttle acuator)- but i don't believe it is this due to the fact it is only hesitation on accelleration.

Lots of luck, and remember- Only buy the throttle cleaner! Do not buy the Carb/ Choke cleaner that is available. They are not the same product!!!!:)

Ps!!!
 

Check the Air Mass Meter that is plugged into your intake pipe that goes to the air-cleaner box. I don't believe you have an Mass Air-Flow Meter as a seperate unit (that came in 1993 3.2L M104 engines). The Air Mass Meter could be failing and not being able to tell the engine management system how much fuel/ air to mix.

Thanks
 

I will update, I apprecaite your replies.. Tom

I always thought that stumbling at idle to 10 MPH was due to a vacuum leak. (air/fuel mix ratio too lean at throttle open). Be shure to check for vacuum leaks before you start throwing parts at it.