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Revs Dropping After Coming To A Stop


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#1 james4563

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Posted 06 February 2019 - 08:30 PM

I've noticed more and more recently that randomly when I pull up to a stop, traffic lights or junction for example, the revs dip down quite low almost like the  car is going to stall and then pick up to normal. Its normally just the one dip in revs and then it's fine but seems quite strange.

 

Any ideas on why that might be, what to check first?

 

MAF, plugs and coil pack etc are all not very old really but it is my everyday drive and I do leave it out in the rain.



#2 Exmantaa

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Posted 06 February 2019 - 11:31 PM

If no obvious fault codes are present, I would thoroughly clean your throttlebody inside and see if that helps.



#3 sford

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Posted 07 February 2019 - 09:57 AM

This symptom presents itself if you disconnect the rear left ABS sensor too. If you have an ABS switch then the sensor may be on it's way out although I'd have thought you would notice an issue with the speedo if this was the case. The rear passenger side is used for speed sensing.

 

But also throttle body. Make sure that is clean. And loom of doom may be worth a clean, just to be sure. 


Edited by sford, 07 February 2019 - 09:58 AM.


#4 SteveA

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Posted 07 February 2019 - 11:29 AM

VSS?



#5 james4563

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Posted 07 February 2019 - 02:58 PM

I assume VSS is the same thing sford is referring too, the speed sensor?

What's the relation between having an issue with the rear left sensor and the revs dropping?

I have an absolute cut off which I believe bypasses the front right abs sensor. So my abs is off and abs dash light is on ofc. I also run atm with rear right abs sensor unplugged, I read this should be done as well as cut of switch??

#6 sford

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Posted 07 February 2019 - 04:27 PM

The rear passenger side is what the speed is taken from, also what to unplug if you don't want to add miles onto your car however you will run into issues with the engine revs dropping to almost a stall when coming to a stand still. If the wiring on the way to the sensor is on it's way then this may manifest when braking and causing strain on that area. I'm only guessing, mine displayed similar symptoms when the sensor wire snapped at the hub but I couldn't diagnose it with the light as I had a cut off fitted too. 

 

The rear right sensor you've unplugged is to do with the proportioning valve I thought. 



#7 james4563

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Posted 07 February 2019 - 05:02 PM

I will try running with my abs all back on and see if any fault present themselves. I did recently have a look at those connections behind the rear passenger wheel arch, one of them is blue I think, they looked in really clean condition but worth another check.

I wonder what makes the revs drop if the ECU cannot read speed properly. Seems a strange link.


Sounds right about the rear right sensor, not sure if it actually did anything or not.

#8 sford

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Posted 07 February 2019 - 05:25 PM

I can't find my pic but this thread has a pic of the wiring at the plug end

 

http://www.vx220.org...d-speedo-issue/

 

A multimeter across those will tell you which is broken or if there is an issue. Connect everything back up first though. 



#9 aquilaproejct

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Posted 07 February 2019 - 07:16 PM

I had the same symptoms when my abs ecu was on the way out. Symptoms presented like a dodgy rear left wheel speed sensor. Turns out it was the ecu.

#10 siztenboots

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Posted 08 February 2019 - 11:05 AM

James to save you time crawling under the car , its not the ABS , or the ECU ( the 2.2 does cut out if speedo signal tampered with )

 

To me this sounds like a vacuum leak , or some unmetered air getting in , downstream of the air mass meter.

 

You could try a reset of fuse 8 to remove any bad learning settings for the idle control , this will also reset the fuel trims back to 0

 

Is this with a new intake manifold?






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