1984 GTI Rabbit Ox Sensor Frequency valve and Control Unit Mystery

Hello
Note this is long with lots of details but I believe it is important to understand what is going on.
I posted a couple of months ago about my 1984 Gti Rabbit. I originally
thought that I had fuel pressure problems.
The car would start immediately and then die 2-3 seconds later, I could restart it and then again it would die 2-3 seconds later. If I started it with my foot on the gas pedal it would start and run at about 2000 rpm however I would need to keep the rpm up for several minutes and then it would be ok. I ruled out losing fuel pressure because of this situation where it would take minutes of holding my foot down a bit and keeping the rpm up at about 2000 rpm. If it was losing fuel pressure like when you change a fuel filter, the idle stumbles for a few seconds or so upon restarting but after about 10 seconds or so the system pressure is built back up.
In my case it takes a couple of minutes of holding the gas pedal down at 2000 rpm before I can release it and then the car can idle by itself. I also noticed that at this time after about two minutes when the car can finally idle by itself the rpm is about 850-900 rpm. After driving it for 30 minutes on the freeway the idle is about 1200 rpm. This may be an indication of the problem, the idle increases as the car comes up to temp.
I checked for vacuum leaks, changed the idle air bypass screw oring, fuel filter, injector orings and injector holder inserts. I also had a spare warmup regulator sitting around and I swapped that too. None of this made a difference.
One it is warmed up it starts and runs fine. I only have this problem after it sits for a while.
I've been driving with these conditions daily for a few months now, freeway driving to and from work about 20 miles each way. A couple of months ago when all this started to happen one day I started it up and the car had all kinds of power like never before also all kinds of throttle response, it was undeliverable, this lasted for about a week and then it went back to normal running conditions, and then my problems started shortly after. Was this a sign a something failing? The frequency valve control unit?
Recently I started to think that, the car starts immediately and then dies, so it must have fuel and then it runs out. I was thinking maybe the frequency valve was not working upon a cold start up. So today after work I dove into it and checked out the O2 sensor and the frequency valve. (Note I do hear the frequency valve buzzing, however I need to check it in the morning cold when the problem exists and listen to see if the valve buzzes for the few seconds that it does run.)
So this is what I measured tonight when I got home, car was up to temp, etc.
I hooked up the dwell meter to the test plug near the cold start valve to measure the dwell of the frequency valve. Upon starting the car the dwell went to 45 degrees steady and the car was hot. This is like open loop conditions however the car was up to temp. After about 1-2 minutes the dwell then went to 50 degrees and heald steady for 3 seconds then it went back to 45 degrees and held steady for 2 seconds then it went to 50 and swung between 50 and 54 degrees. I turned the car off and restarted it and it did the same thing, went through this weird cycle where it looks like it goes open loop and then up to 50 (solid) back to 45(solid) then swings between 50-54 and pretty mush stays here swinging between 50-54. I was surprised I thought that it would be either open loop or not, is there some sequence it goes through even if the car is up to temp? The fan was coming on.
So I took a voltmeter and measured the ox sensor voltage with it still connected, and I measured .4-.6 Volts as the dwell swung between 50-54 degrees. I then disconnected the ox sensor and grounded the green wire (the one that goes to the control unit), the dwell slowly increased (within about 5 sec) went up to 74 degrees, stayed there for a few seconds then slowly went down to 36 degrees, the ox sensor read .8 V. I read that, upon grounding the wire to the control unit that this would simulate a lean condition .8V - 1V and that the dwell should go to 75 degrees or higher. My dwell increased but then cycled back down? Is this normal?
I read on a Volvo web site a CIS discussion that upon grounding the wire the system would compensate for the lean / rich condition. As it compensates the lean rich condition will eventually swing the other way and the entire procedure will start all over again? Is this true, that if you disconnect the green wire from the ox sensor and ground it that the dwell will swing up and then back down? I've read previous posts on this group stating that it would swing up to 75 degrees and stay there. Why would the dwell go up and then come back down with the wire ground. I would think that it would go to one extreme and stay there.
Lastly, if you are still with me, another odd thing I noticed. This is the last test / experiment I did. The car was up to temp; I disconnected the ox sensor temp switch. This switch opens above 77F and shorts below 68F. So I ohmed out the switch and it was open as expected therefore leaving the connector off the switch made no difference. The car was idling and the dwell was between 50-56 degrees. Just for the hell of it I took a small piece of wire and I shorted out the connector. This would simulate a below 68F water temp and put the system into open loop? Well the wire shorted across the connector the dwell went up to 60 degrees and stayed there. What give? Shouldn't it have gone open loop to 45 degrees?
Do I have a bad control unit?
I repeated all of the above tests 3 times and got the same results.
Thanks for you time.
Ideas?
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Only one, and it is a SWAG of all SWAGs, and given with the caveat that I am *NOT* familiar with that particular FI system.
Disclaimers completed, and making the assumption that you have changed the fuel filter: Could you have a bad/partially collapsed fuel line such that it does not fully open up until it gets warmed up some? Codicil to this SWAG... sludge in the fuel tank could give this symptom until it is dispersed by the circulating gas...
Remember, I warned you these were SWAGs, and based on eliminating the potential mechanical problems before looking for electronic trouble.
Peter Wieck Wyncote, PA
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Hello
Today I went to the junkyard and got a ox sensor control unit and the problem still exists. I kinda doubt it is bad and failed in the same way. I reran the tests for the hell of it and all the results I got yesterday in my orignal post are the same. I put the original unit back in.
So I need to go back and troubleshoot, things that are running through my mind, worn fuel dist, ignition dist, ignition control module?.
I am going to remove the ducting for the air intake and clean the throttle body and the air flow plate. This way I can also inspect the hoses and boots.

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OK When your engine starts it needs certain items to function properly in this case: Fuel Control Pressure Regulator (test with fuel pressure gauge) Sensor for the 02 Sensor system Properly adjusted Fuel Distributor Properly tuned engine Functioning Aux. Air Regulator (did you check this out?) And other items like proper ign and fuel delivery
Is your only problem the engine idle speed when cold and hot? The Aux. Air Regulator will allow the idle to be higher on a cold engine and then will close as the engine warms up reducing the extra air into the engine slightly. It has a heating element to help it close and is also heated by the engine. Also you might have other Air Regulators if this vehicle has A/C.
--
later,
dave
(One out of many daves)
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Time to attach your fuel pressure guage and check that system out as per Bentley manual. Pay attention to residual pressure.
Also inspect all fuel injectors for drips when using pressure guage.
On Fri, 20 Jul 2007 18:35:50 -0700, "Tube Audio"

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Jim and Dave thanks for the replies.
I got up this morning and hooked up a dwell meter to the ox sensor test port, had the meter leaning against the front windshield. I started the car and the dwell went up to 60 degrees and stayed there for a few minutes then came down. The outside temp is 62 degrees and the car sat overnight.
This doesn't seem correct the dwell should be 45 degrees open loop.
Anyway I traced all the wires coming through the firewall on the passengers side, the wires from the ox sensor control unit.
I noticed a connector with two red wires in and two red wires out, it was just below where the heater hoses go through the firewall. This is part of the wiring to the ox sensor control unit. Perhaps it is the 12V supply voltage to the unit. Anyway the connector looked pretty bad, so I unplugged it and the contacts were all corroded and gunked up. (I recently replace my heater core and had the water draining in this area, the trouble started soon after changing the heater core.. hint hint) So I took my can of deoxit, electrical contact cleaner and a small wire brush to the contacts and got them shiny.
As the car is running and up to temp I will have to let it cool down to see if this is the fix.
The supply voltage to the control unit could not have been 12V due to the voltage drop in the corroded contacts. This may point to the two strange things I saw recently. Upon starting the dwell was 0 degrees and the tach in the dash showed 0 rpm when the car was running, this only happened once and just lasted for a few seconds.
Otherwise I will do as both of you said and get a pressure gauge on the system. I don't have one. A good friend does but doesn't have the cis fittings, or was thinking about buying the one from jc jitney for $60.
Thanks for the input

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hmmm 60 degrees means it it running very lean or the 02 sensor just ain't working at that time. Your 1-wire sensor takes some time to heat up and work so the 02 system should not be "online" yet.
I need to read up on this but I thought the meter should be reading '0' until the 02 system comes online. The system is allowed to come online when the coolant temperature switch completes the circuit. Not sure of this though and it should not matter since I have bypassed my switch on my '83 GTi engine in my Audi 4000s and I don't have trouble.
CHECK THAT AUX. AIR REGULATOR!!! When the engine is at normal temp then you can easily pinch one of its hoses to see if the idle remains the same. If it drops a lot then I suspect a problem with it. ;-)
You can test your 02 system out by unplugging the 02 sensor when the engine is cold to see if that changes anything too.
--
later,
dave
(One out of many daves)
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I still believe it's vapour lock. Sometimes it takes some time to flush out the trapped air. Just do a fuel pressure test with a simple pressure gauge. Turn off (hot) engine and watch the gauge. It should hold about 14psi of pressure for at least 20min.
SFC

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