Confusing Problem
 

Hi guys,

I have a matter that I confusing me a lot, my idle is perfect. Only during driving as soon as I slightly remove my foot from the gasoline pedal, I feel like as I turn ignition switch off and when put it back I feel like as I turn on ignition switch back again, where to start troubleshooting this problem. Any ideas would be great and thanks in advance.

You are confusing me a lot. I don't understand what the problem is.

"When I put my foot on the gas, the car goes"

"When I take my foot off the gas, the car stops going"

:D ;) :D

More information would help:

What year and type of car?

A better description of symptoms would also help. Do you mean that your idle is okay when stopped and in Park, but when you drive and slow down the idle drops very low and when you start to accelerate the idle is very slow to come back up?

Can you post the RPM when you're idling in Park, then idling with your foot on the brake in Drive?

If you are getting misfires that vary with the throttle position, I would look at the airflow sensor, but with the Bosch Jetronic on the 91 560 SEL you may want to get a professional diagnosis before guessing at parts.

Obviously doing the best he can to explain the trouble in English. This is what it sounds like he's saying to me: the car starts and idles fine, when he starts to give it gas it's also okay, but when he lets off on the gas it wants to stall. When he gives it gas again it acts normal again.

If that's correct, then it would help to know what model, year and engine it is.
What happens after letting up on the pedal if you don't give it gas again, will it actually stall, or does it just give a big hesitation and catch an idle again?
Does it only happen cold?, warm?, all the time?
Was there anything unusual you noticed before this started to happen?

First thing that came to mind was cracked hoses on the IAC, or a bad IAC valve. But that might give a few indications it was going bad before getting to this point.
Also the throttle micro switch that lets the fuel system know it should be in idle mode might have a similar affect if it isn't working properly?

Car model 91, 560sel Eur spec, there is no problem at all the times, idle is 650rpm when in park or on nuetral. 600rpm when in D and foot on brake. May be I explain it this way much better, when I drive the car, there is a smooth, no hesitation in acceleration no stalling at all. When I slightly take off my foot from the gas pedal, there is a feeling like power is being cut off and car start just rolling, when I just press little on gas pedal, like power does come back again and car has just received a little push from the back. No air vacuum leak is found, idle control valve , air breather hoses are all okay. Cold start is achieved within 2 seconds only. Car is neither stalled on warming up nor in driving mode.

Sounds almost like the behavior of electric golf carts--let off the accelerator and the motor disengages, altho the cart keeps rolling. Touch the accelerator even slightly, and the motor re-engages. Maybe his problem, too, is electrical in nature.

I got my problem solved, I guess the throttle switch was the problem. I removed the throttle body, cleaned and readjusted the throttle micro switch, the problem is gone.:D Great thanks to those gave me help.