# CIS Lambda Frequency Valve Question



## ectonvw (Mar 15, 2001)

1984 Rabbit Convertible, 1.8 JH, CIS Lambda
First cool night of the year temps in the low 40s. Took car out of warm garage, drove to work ran fine. Left at lunch to go swimming, car would not idle and stumbled a lot. Managed to nurse it home (5 miles). Adjusted TB idle screw so it would idle. No obvious vacuum leaks.
The main thing I noticed was that the buzzing from the frequency valve is now very quiet. When the car was running right the buzzing was very loud, you could hear it hood closed from several feet away. Now, you almost have to put your ear on it to hear it. So i'm suspecting something in the Lambda are of the FI. Harness is still connected to the frequency valve.
Looked at my Bosch FI book last night, I'm thinking I need to check my O2 sensor and the thermotime switch. Does anyone have any more suggestions as to what might have gone wrong? Really seems odd that something could fail so completely after sitting for only 4 hours.
Still ran poorly after sitting one night in warm garage.
Thanks in advance for your help,
George


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## ABA Scirocco (May 30, 2001)

*Re: CIS Lambda Frequency Valve Question (ectonvw)*


_Quote, originally posted by *ectonvw* »_The main thing I noticed was that the buzzing from the frequency valve is now very quiet. 


That means there's definitely wrong with the frequency valve or it's related wiring and circuitry. The problem doesn't lie with the O2 sensor or thermotime switch because even if these were faulty the frequency valve would still buzz. 
Here's how the circuit is set up; the frequency valve gets it's power from the the fuel pump relay, in some cases through a secondary relay, the frequency is grounded through the ECU, the ECU modulates the frequency valve (i.e. makes it buzz) by manipulating the ground.
Check out the CIS pages here http://www.geocities.com/jonnyguru/vw/ to gain better understanding of how the system works and how it's adjusted. 
I had a problem with the system on my car that had the EXACT same symptoms as yours except that my problem was intermitant. In my case, the problem turned out to be a bad ground connection for the ECU. The ground wire attaches to the engine at the cold start valve on my car, on others it may connect at the corner of the valve cover. So I'd start by cleaning all the ground connections attached to the engine and check the frequency valve and ecu for power.
FWIW, my money's on the ground wire, it's a very common problem on older VW's in fact in over 20 years of driving these cars almost very electrical problem I've every had has been the result of a bad ground.
Good luck


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## ectonvw (Mar 15, 2001)

ABA - Thanks a lot. I will check this out. This car has definitely had its share of electrical/ground issues.
I had the ground for the Auxiliary Air valve go out a few years ago, and it caused all sorts of problems. It took me forever to diagnose that one!


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## ectonvw (Mar 15, 2001)

I cleaned the ground at the Cold Start Valve - that did not help. I pulled the connector at the frequency valve - there is no 12V at the connector with the engine on. That is the problem. Consulted Bentley - looks like there is a "Fuel Injection Power Supply Relay" #15 which supplies power to the Lambda system - that is next to be checked.


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## BlackTie+ (Oct 17, 2003)

*Re: (ectonvw)*

Wow, I am going through all this right now too. Staying tuned....


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## ABA Scirocco (May 30, 2001)

*Re: (ectonvw)*


_Quote, originally posted by *ectonvw* »_- that did not help. I pulled the connector at the frequency valve - there is no 12V at the connector with the engine on. 

Sounds like you're on the right track. BTW, when you says you checked it with the engine on, do you mean, the engine was running or you just had the key turned on? I ask this because the frequency valve normally only gets power when the fuel pump relay is energized so power at the FV needs to be checked with the engine running OR the fuel pump relay bypassed


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## ectonvw (Mar 15, 2001)

Yes the engine was running - not well, but running.
I pulled Relay #15 - the Fuel Injection Power Supply relay and bench tested it. It does not work, so I think this is the problem.
Called VW - they say the relay part #171 906 381 is NLA. Called a Bosch Parts place I've had good luck with - they can get it on Monday for $20. I'll give that a shot and fill everyone in on Monday or Tuesday.


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## ectonvw (Mar 15, 2001)

Picked up the replacement relay today. It is Bosch Part #0332015006. I'll see if I can get things working this evening.


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## ectonvw (Mar 15, 2001)

Success. Replaced the relay, once again had 12V on the frequency valve connector. Replaced the connector, valve started buzzing like normal. Car now runs great again.
ABA, thanks for your help! BlackTie+, I hope my experience helps you out. I think I might buy a new fuel pump relay, just in case!


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## BlackTie+ (Oct 17, 2003)

*Re: (ectonvw)*

I think this does help me out. Can you point me to where you purchased your relay?


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## ectonvw (Mar 15, 2001)

I bought it from an independent parts place that handles Bosch parts. It cost me $20.44. I'd think probably any parts place could get the part using the Bosch part number. 
I actually gave the parts place the VW part number and somehow they cross referenced it to the Bosch part number.
I bought the relay from John at Mount Airy Auto Parts in Flourtown, PA (outside of Philadelphia). 215-836-5278. Really nothing unique about this parts place, except they do have a Bosch sign out front!
Hope this helps.


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## BlackTie+ (Oct 17, 2003)

*Re: (ectonvw)*

Thank you! http://****************.com/smile/emthup.gif 
This is a nice example of how the vortex can really shine.


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## ectonvw (Mar 15, 2001)

Absolutely. The level of help you can get here is incredible!


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## Peter Tong (Jun 17, 1999)

*Re: (ectonvw)*

I also had this happen to me years ago (back in 91 or so)... all I can remember is that the car would run but not well! Glad you found the problem...


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