Does anybody know?
Thread Starter
Newbie
Joined: Sep 2016
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A170(W169) full manual
Does anybody know?
I am trying to find out why my RPM goes directly to idle when shifting in neutral. My engine idle is 750 rpm. Some people say that, when the car is moving and you shift in neutral to a manual gearbox car, the RPM should stay higher, at about 1000 rpm. Only after the car has stopped, the RPM should go to idle. My car doesn't do that.
I discovered something like this on a different site:”Elevated idle speed during deceleration is an emissions strategy to maintain clean exhaust output and prevent overheating of the catalytic converter. The PCM uses speed sensor input to determine when the vehicle has stopped , then return the idle speed to normal.”
My A class, petrol engine, manual transmission, no ACS, no cruise control, W169/2004 model, doesn't maintain RPM higher than idle, while in motion. I suspected a clutch switch malfunction, but there is no error on STAR diagnosis.
I know it is not normal to drive with shift lever in neutral position. This situation can be noticed when approaching a red light and I press clutch pedal, set neutral, than release the clutch pedal.
I would like to know if my car should have elevated RPM when in neutral and the car not stopped. Thank you.
I discovered something like this on a different site:”Elevated idle speed during deceleration is an emissions strategy to maintain clean exhaust output and prevent overheating of the catalytic converter. The PCM uses speed sensor input to determine when the vehicle has stopped , then return the idle speed to normal.”
My A class, petrol engine, manual transmission, no ACS, no cruise control, W169/2004 model, doesn't maintain RPM higher than idle, while in motion. I suspected a clutch switch malfunction, but there is no error on STAR diagnosis.
I know it is not normal to drive with shift lever in neutral position. This situation can be noticed when approaching a red light and I press clutch pedal, set neutral, than release the clutch pedal.
I would like to know if my car should have elevated RPM when in neutral and the car not stopped. Thank you.
Junior Member
Joined: Apr 2016
Posts: 58
Likes: 9
From: England
...
Sorry George, can't help with your question, I'm afraid - never driven a manual and know nothing about them. Just didn't want you to think your post is being ignored.
If you're looking into fitting DRLs, or a dashcam, or footwell lights, etc, etc - I'd be happy to share my experience
If you're looking into fitting DRLs, or a dashcam, or footwell lights, etc, etc - I'd be happy to share my experience
Thread Starter
Newbie
Joined: Sep 2016
Posts: 7
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A170(W169) full manual
OK Chode McBlob, thanks anyway.
I asked an automatic gearbox owner about this. In his case, the RPM indicator stayed higher than idle while the car was rolling. Then, he applied brake and stopped rolling...the RPM indicator went to idle. I think, even if i have a manual transmission, the RPM should stay higher than idle as long as the car is moving.
I asked an automatic gearbox owner about this. In his case, the RPM indicator stayed higher than idle while the car was rolling. Then, he applied brake and stopped rolling...the RPM indicator went to idle. I think, even if i have a manual transmission, the RPM should stay higher than idle as long as the car is moving.
MBWorld Fanatic!
Joined: Jun 2011
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From: Cape town
not a merc
There will not be an error because there is no fault. I said check coding!
But honestly why would you bother with such a feature? It has nothing to do with emissions. Sometimes that feature is implemented to help serve as an anti jerk control when you travel at very low speeds in stop start traffic. If your A class drives fine I would not worry about it. I will take note next time I work on a manual to see how the idling in neutral behaves.
Good luck
But honestly why would you bother with such a feature? It has nothing to do with emissions. Sometimes that feature is implemented to help serve as an anti jerk control when you travel at very low speeds in stop start traffic. If your A class drives fine I would not worry about it. I will take note next time I work on a manual to see how the idling in neutral behaves.
Good luck
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Thread Starter
Newbie
Joined: Sep 2016
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A170(W169) full manual
Revs drop slowly between shifts. Could be clutch pedal switch, or borken PCV(Purge Control Valve)...still searching.
By coding did you mean to check if codes that are written on injectors are programmed in ECU's soft?...suchlike diesel engines?
I suspect Check Valve inside Fuel Pump, also.
By coding did you mean to check if codes that are written on injectors are programmed in ECU's soft?...suchlike diesel engines?
I suspect Check Valve inside Fuel Pump, also.
Last edited by george_w169; Feb 27, 2018 at 06:53 AM. Reason: I forgot something
