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you don't want to put a voltmeter set to Ohms to the harness wires, thats for sure!
Testing Volts is fine, just attach probes before switching on IGN, to be safe.

No great help to your problem, but this is what is inside the TPS:)
One is Fiat X1/9 (but same Bosch part# as our S4 spider) and the other is a volvo (looks identical except it's a mirror image)
 

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Discussion Starter #22
Once again, thanks very much for the suggestions, very much appreciated in getting this mystery solved.
I've rechecked the TPS, and indeed it does switch at WOT, I just didn't open it enough last time when checking. The TPS is working correctly.
I cleaned out the throttle body as well, it was a bit dirty, but not enough to cause any trouble IMO.
I did however find 2 definite problems. I checked again the operation of the fuel vapour solenoid, and there is not enough voltage on it to activate the solenoid. As the switched side is ground, I disconnected this wire, and grounded the solenoid manually, and could feel and hear the "click" and also tested by blowing through it, and it does operate, closed when off and open when activated. It seems like I must have a poor connection between the ECU and the solenoid, since when it should be ON, the switch is only pulling it down to 10.5V rather than full ground. The resistance across the solenoid is about 38 Ohm, so this means with a 3.2V drop there is 8mA flowing through... Something wrong here, need to check the wire back to the ECU.
But the bigger and more likely cause of all the trouble is that the set screw on the throttle seems to have been “adjusted” at some point, as it was about 5 turns out from even touching. I measured the output of the O2 sensor, and even when the idle seems stable, you could see it was hunting as the voltage was oscillating between .2 and .8V. I adjusted the throttle so that it is open ever so slightly (about ¼ turn from touching) and the idle is much better as is the transient (foot off throttle for example, it stabilizes at idle much smoother now). Seems that I need to set the throttle back in the calibrated position. Any tricks to getting it to the right position? I was going to monitor the O2 sensor output and find the spot where this control stops hunting and (hopefully) settles on stoic (0.5V for a NB O2 sensor right?) Is there some other method to recalibrating the throttle “in-car”?
By the way, regarding taking measurements with the DMM, for sure (as Dom said) I am not taking resistance measurements back to the ECU, only resistance of potentiometer sensors (disconnected) and voltage measurements. Voltage measurements are "harmless" as they are not injecting a current into the circuit (to calculate resistance). Thanks though for the warning :)
 

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But Mad North-Northwest
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Whoa there, Tex. The O2 sensor voltage output is SUPPOSED to oscillate between 0.2-0.8V at idle or cruise. It should average about 0.45V but it will NOT be a steady voltage.
 

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Discussion Starter #24
Ah, got it. Didn’t realize that narrow band sensor control strategy was to « flip-flop » over lambda = 1, but makes perfect sense when you think about it.
So is there a technique to resetting the throttle stop position with the throttle body still on the engine? Should I just adjust it until the O2 sensor output oscillation is symmetric? (I think I will hook up an oscilloscope to get at better picture of what the sensor output is really doing)
Is there another technique for re-setting the calibrated stop on the throttle?
Second question is for the evaporative recovery solenoid, does it come on systematically with the ignition, or is it controlled somehow on some other parameter (like temp?)? Seems like if it was always on with ignition, then they would have just grounded one side of the solenoid and the power would be switched form the relay as it is currently. Was thinking about just grounding one side of it to avoid hunting for a voltage drop in the wire harness, or having to disconnect the big connector to the ECU, I’m worried about upsetting some other fragile connection in the process….
 

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Discussion Starter #25 (Edited)
Curveball

Just as I was thinking that this issue was not causing me enough grief (I am late getting my smog test done….), I had another curveball thrown at me today. The idle went from being somewhat stable (and better than before) to sounding like it was running on 3 cylinders all of a sudden. Sigh…. I suspected the ignition, so swapped all kinds of components out and eliminated this as a potential cause, but did confirm that it was cylinder 1 seemed to be running much richer that the others (based on the spark plug colour). In despair as I was leaning on the intake plenum looking at the motor run like a tractor, I felt the front side of the intake plenum was almost icy cold…. Long story short, the fuel pressure regulator is spitting all kinds of un-metered gasoline drops into the plenum through the vacuum hose that is just below that one for the evap solenoid. I presume it is not supposed to do that…. <sarcasm>.
Guess I’ll start looking around for a new fuel rail, or complete manifold assy (doesn’t look like the regulator is easily replaceable as a component). I sure hope that I haven’t poisoned the new catalytic converter that just installed.
In the meantime, if someone knows how to re-calibrate the throttle set screw (if I ever get to this stage!), would very much appreciate knowing how to do it.
Thanks
 

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yes fuel should not be in the vacuum hose....the other hose is the return hose!

Likely a bad FPR. Pretty sure you can swop out the fuel pressure regulator w/o fiddling about with the fuel rail though.....I believe it just unbolts off the end of the rail, OR, even just pops into the rail with an O seal, and the bracket holds it in, something like that (I'll double check that, I got a spare in the cellar!)
 

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But Mad North-Northwest
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Yeah, that's not good. Rock Auto carries just the regulator.

No idea how to calibrate the throttle stop, but I don't think it's very sensitive to that setting on the S4 due to the active idle control. Just make sure wherever you set the stop that the TPS is set up right.
 

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just FYI: be sure to get the correct regulator. IAP list a motronic one that is screw on (no good)...for instance

For the S4 it pushes on and seals with an O ring.....then you put the 2 small bolts back on to hold it all in place.

correct S4 type is the grimy one here:)
http://www.alfabb.com/bb/forums/5003226-post4.html

As for throttle stop: WSM uses a Solex flow meter to calculate flow thru the 'closed' butterfly with the throttle body removed from the car. I believe they call it a fluxing test on later alfas. (WSM values: 'air leakage with throttle disc in closed position 240 thru 260 scale N') and calls the stop an "air flow rate adjusting screw"!

...I doubt it is rocket science, as long as the butterfly is just the tiniest bit open...a bit of experimenting...trouble is you can only see the butterfly when the hard plastic inlet pipe is removed.
 

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When I find messed-with throttle stops on an S3 here is what I do: back out the stop screw until the throttle is closed. Turn it in until it just about to contact the throttle stop. Start the engine and adjust the stop screw until it increases the idle speed by ~ 50 rpm over completely closed.

Now, on a Series 3 (L-jet) the idle speed is set by the idle air device (squeezes an O-ring to vary the idle air allowed to enter). I am not sure how to do this with a Series 4 because they have the IAC device. Perhaps you can disable it temporarily?
 

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Discussion Starter #31
After a weekend away, got a chance to replace the fuel pressure regulator. I ended up getting a Bosch (same part number as the one I removed), turns out this parts is also used on many VW's of the same era. There seems to be some issues with the regular part suppliers about the right part number (exactly as Dom pointed out, threaded vs. nipple connections). I didn't want to go down that foxhole, so just got the right Bosch part number (0 280 160 235) which is a 3bar regulator by the way.
Put it in and the car runs (dare I say...) as it should. I fiddled around with the idle stop, and it doesn't seem to be too sensitive, I guess the IAC is simply compensating to get the right amount of air in there. Here is what I ended up doing : Found the point where the set screw comes in contact with the throttle (using a very thin feeler gauge is good for this), marked the point, then turned the screw CW (in) to see where TPS sensor trips open (bottom two pins, normally closed), found this point then turned the set screw back (CCW) to see when the TPS closes again. There is, of course some hysteresis in the switch. This is shown in the picture below.
The idle seems pretty insensitive to the position of the set screw, as long as it is between the first contact point and the point where the TPS opens. The idle does increase as soon as the TPS opens, and the idle does go down when the throttle is fully closed, but in between these two positions, i did not notice much difference, so I left it at the halfway point.
Can anyone confirm that the TPS open and close positions are more or less right?
The last thing I need to address is the evap solenoid not getting a good ground switch to come on, I think what I will do is just ground the neg side of the coil so that the solenoid comes on when the ignition is on since the 12V is supplied by the switched relay. I believe that the solenoid is always on with ignition unless it is cold, in which case it either waits for the coolant temp to get to a min value or uses some other trigger. Does anyone know the switching logic for the evap solenoid?
 

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Discussion Starter #32
I just read the link about setting the throttle stop on a TS, I beleive that this should be identical to the S4, will give that a try to dial it in a bit more
 

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But Mad North-Northwest
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The TPS position is adjustable. So using where it's at now may or may not be a decent guide.

The last thing I need to address is the evap solenoid not getting a good ground switch to come on, I think what I will do is just ground the neg side of the coil so that the solenoid comes on when the ignition is on since the 12V is supplied by the switched relay. I believe that the solenoid is always on with ignition unless it is cold, in which case it either waits for the coolant temp to get to a min value or uses some other trigger. Does anyone know the switching logic for the evap solenoid?
Not a great idea, since IIRC the Motronic actually adjusts the mixture slightly when it opens the solenoid to account for the additional air. Are you sure it's not ever opening the solenoid? You may just be checking for ground during times when the solenoid is supposed to be closed: it's not open all the time.
 

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Discussion Starter #34
Not a great idea, since IIRC the Motronic actually adjusts the mixture slightly when it opens the solenoid to account for the additional air. Are you sure it's not ever opening the solenoid? You may just be checking for ground during times when the solenoid is supposed to be closed: it's not open all the time.
You could be right, I've been assuming that it is open when the engine is warm, but I know what happens when one assumes...

I'll check it in a few more operating conditions to see whether or not it is turning on or not. Thanks for the tip.
 

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Also, if the solenoid is malfunctioning you will get a check engine light and code. This happened to me so I know the self-test works. So I'm thinking you may not actually have a problem.
 

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Discussion Starter #36
Thanks Gubi, that is good to know. I've never had a check engine code for anything other than O2 sensor out of range (1223).

Gubi or Dom (or anyone with a 91 spider) would any of you be able to do a quick voltage check at the evap solenoid to see if your is on when the car is running and at operating temp?

I am going to drive the car around for a day or two, and if there are no more symptoms (or check engine lights!), I will go in for my smog re-test. finger crossed!
 

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Discussion Starter #37
Believe it or not, I just glanced through the owner's manual (what one does once the problem is more or less solved...)and found the following paragraph about the evap solenoid :

"When the engine is operating under load conditions, with a considerable flow of air into the engine, the injection and ignition ECU provides for the opening of the "evaporative" solenoid (14)"

So it would seem it is NOT on all the time, just under load. I am going to assume that mine is functioning correctly since I've tested the solenoid itself, checked that the lines aren't plugged, and don't get a check engine light concerning it. Thanks for prompting me to investigate this further Gubi.
 

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so just to sum up....the root cause was in fact a bad fuel pressure regulator, that correct?

Glad it's fixed and good luck with the Smog test!
 

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Discussion Starter #39
Yes, it seems that the fuel pressure regulator was the cause of the idle problems. Thanks very much Dom and Gubi for getting me through this one!!
 

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Discussion Starter #40
Passed the smog test with flying colours :
previous / limit / new
HC (ppm) 199 / 121 / 3
CO(%) .16 / .76 / 0
NO (ppm) 2842 / 807 / 0

no oddities at all driving the car, I think it is safe to say that the problem is solved!

Thanks again, vielen danke for all the help Dom and Gubi!
 
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