I love this List!!

Dennis,

Thanks a lot for that explanation. It really helps clarify how this engine operation is controlled, and clears up misconceptions on my part. I'm going to go back now and revisit the whole issue of idle speed setup and adjustment, and do some trouble shooting.

Thanks again.

John

John Rodgers Clayartist and Moldmaker 88'GL VW Bus Driver Chelsea, AL Http://www.moldhaus.com

On 8/18/2011 12:44 AM, Dennis Haynes wrote: > > -----Original Message----- > From: Dennis Haynes [mailto:d23haynes57@hotmail.com] > Sent: Thursday, August 18, 2011 1:32 AM > To: 'John Rodgers'; vanagon@GERRY.VANAGON.COM > Subject: RE: All Is Not Well in Air Conditioning Land > > Here goes! > The ECU does absolutely nothing to regulate or stabilize idle speed. The > idle speed control is an afterthought to help compensate for O2 sensor > fluctuations, alternator loading, power Steering and air conditioning. The > latter two which are not as common in Europe in those years. > > Now there are some inputs that are shared between the ECU and the idle > controller. Mostly engine temperature and of course speed. > > The real proper way to set the idle speed is by measuring the current or the > duty cycle of the idle valve. Instructions in the good book, (Bentley). > > With the idle valve electrically disconnected it should be completely > closed. Test by pinching or blocking off a hose. If you can affect the idle > speed by pinching the hose with it un plugged the valve is no good. > Connecting the valve and having the engine drop in idle speed is also an > indication of a valve problem. The controller should only be able to open > it. A defective valve (weak-broken spring or stuck plunger), will sometimes > get pulled closed from the low frequency signal from the controller but this > again is a sign of a problem. > > Of most importance is to have the throttle switch working and the basic > settings correct. When warm the engine should be able to idle reliably at a > set RPM without the valve. The AC load will drop the idle speed but it > should not stall the engine. > > Run away (high idle) speed is often the result of a bad connection to the > temp 2 sensor. Remember both the ECU and idle controller use this sensor and > the sensor sinks the signal to the chassis. Thus any high resistance tells > both the ECU and the controller that the engine is cold. Really cold engines > need high idle, advanced ignition timing and no O2 sensor control. Guess > what! 1,500 to 2,000 rpm idle speed. Especially if AC or PS boost is added. > > Dennis > > > -----Original Message----- > From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of > John Rodgers > Sent: Wednesday, August 17, 2011 11:03 AM > To: vanagon@GERRY.VANAGON.COM > Subject: Re: All Is Not Well in Air Conditioning Land > > As I understand it - and my interpretation may be off here so maybe a more > knowledgeable person can correct me - the idle circuit includes the Idle > Stabilizer Valve( ISV - top of the engine) and the Idle Stabilizer Control > (ISC - in front of the right hand brake light), and the Electronic Control > Unit(ECU). The ECU receives inputs from the Temp II sensor and from the O2 > sensor. These inputs change as the engine warms up. The ECU uses the inputs > - and some others - to adjust the idle speed through the Idle Circuit so the > engine does not stall when the AC is on. > I think I have read somwhere that it is set up to kick the RPM up if it > falls below 1300-1500 rpm, preventing the eninge from stalling, say, at at > stop light, when normally the engine would drop back to idle. Of course if > that happened, with the load of the AC on it, it would stall, so the ECU > works to keep the engine running fast enough to create the horsepower needed > to run the AC - which by the way, is around 5 hp. > > Make sure all of your vacuum lines are connected and there are no leaks. > Then set the idle RPM per the Bentley. Be sure you remember how many turns > of the idle speed screw you used. You may want to go back to where you were > with it. Check operation after adjustment. > > Beyond that - we are paddling the same boat I'm afraid. I haven't figured > out why mine wants to idle to fast, even after adjustments. > > Good luck. > > John > > John Rodgers > Clayartist and Moldmaker > 88'GL VW Bus Driver > Chelsea, AL > Http://www.moldhaus.com > > > On 8/17/2011 7:42 AM, Harry Hoffman wrote: >> Hi John, >> >> I'd be very interested in hearing what you find out. >> >> I just got my A/C recharged and working (it feels great too) but now >> idle is 1k+ and anything lower and the engine will die (with or >> without A/C running). >> >> Cheers, >> harry >> >> On 08/16/2011 11:46 PM, John Rodgers wrote: >>> After all my excitement about having air conditioning - a new >>> problem has reared it's ugly head. Out of control RPM. >>> >>> After I got my AC system working - I noted the engine idled way to >>> fast, even with the AC turned off. Work associated with the AC effort >>> was getting the vacuum lines connected correctly - which they were >>> not. Now, with everything as it should be - apparently - the engine >>> idles to fast, as I said, even with the AC off. I went through the >>> idle adjustment procedure per Bentley, and with O2 sensor and ISV >>> disconnected, and engine warm, it idled perfect - 850 +- rpm. When I >>> reconnected - the engine died. Repeated the procedure, it will not >>> idle when O2 and ISV are reconnected, I could only get the rpm by >>> adjusting while the ISV is connected - and it is approximately >>> correct > but still is a bit to fast. >>> I can leave the ISV disconnected and just run it - which i have done >>> for years, but now I have the AC working, I need that to work in >>> conjuncton with the AC to keep the engine from stalling and it's not > happening. >>> Anyone have any ideas? >>> >>> Thanks, >>> >>> John >>> >>> -- >>> John Rodgers >>> Clayartist and Moldmaker >>> 88'GL VW Bus Driver >>> Chelsea, AL >>> Http://www.moldhaus.com >>> > > > >