# A little help with my '86 QSW please



## Row1Rich (Sep 11, 2001)

Got a little issue I need some help diagnosing, thanx in advance.

The car starts up beautifully every time and purrs like a kitten. However, when it reaches temperature, the idle rises and when you give it any throttle it sputters and bucks. Seems to be running really rich. If I unplug the lead to the ? on the end of the intake pictured below, the idle drops to normal and the car drives fine. If I leave the plug off and try to start it when cold it doesn't like it and takes repeated attempts.
Any ideas? It started doing this after I mis-shifted and revved the engine really fast but it didn't over rev. :facepalm: I caught it before it hit redline. eace:


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## jeroland (May 29, 2010)

The Bentley manual says that Bosch part you have pictured is the Differential Pressure Regulator. You should do a quick search on it. From what I understand the DPR tells the ECU how to adjust the mixture based on coolant temperature and the oxygen sensor. Good luck with that.


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## AudiSportA4 (Mar 3, 2002)

IAT?


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## ziddey (Apr 16, 2006)

head to the cis section in technical, and read up on how to tune cis-e.

fine fueling beyond the baseline mixture is controlled via the DPR.

It sounds like something happened that's causing your mixture to be outside of the threshold that the ECU can adapt for. Most likely, you've sprung a vacuum leak somewhere.


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## Row1Rich (Sep 11, 2001)

ziddey said:


> head to the cis section in technical, and read up on how to tune cis-e.
> 
> fine fueling beyond the baseline mixture is controlled via the DPR.
> 
> It sounds like something happened that's causing your mixture to be outside of the threshold that the ECU can adapt for. Most likely, you've sprung a vacuum leak somewhere.


Thanx Ziddey, could the mis-shift explain the vacuum leak? I shifted form 4th - 3rd instead of 4th - 5th. Didn't hit redline but the engine revved really quickly through the rev range.


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## ziddey (Apr 16, 2006)

it shouldn't, but it's possible, especially if your engine mounts are worn, and a vacuum line was on the brink of breaking off.


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## Row1Rich (Sep 11, 2001)

ziddey said:


> it shouldn't, but it's possible, especially if your engine mounts are worn, and a vacuum line was on the brink of breaking off.


My mounts are good, but still a good suggestion. I'll check it out.


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## Row1Rich (Sep 11, 2001)

New coolant sensor fixed the problem, thanx for all the suggestions :thumbup:


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