Idle up, idle down, dies

[mark944T]

I know this has been covered before, but still looking for advice as I think my problem is unique.

I have a 1980SC and it idles up and down rapidly warm or cold. If I don’t give it gas it dies. I took it to a shop (well known) when it only did it when it was cold. Now it does it all the time, cold or warm. Shop doesn’t know why and said they are not at fault for it being worse.

I have some mechanical abilities and want to fix it myself. If I need to buy some special equipment I’m ok with that. Thanks for any advice.

[boyt911sc]

Originally Posted by mark944T

I know this has been covered before, but still looking for advice as I think my problem is unique.

I have a 1980SC and it idles up and down rapidly warm or cold. If I don’t give it gas it dies. I took it to a shop (well known) when it only did it when it was cold. Now it does it all the time, cold or warm. Shop doesn’t know why and said they are not at fault for it being worse.

I have some mechanical abilities and want to fix it myself. If I need to buy some special equipment I’m ok with that. Thanks for any advice.

Mark,

You need a set of pressure gauge to check your fuel pressures (CCP, WCP, & SP). A homemade smoke tester will help you find those hard to find air leaks. A shop with gas analyzer could read measure or check your fuel mixture. Is your WUR -072? Keep us posted.

Tony

[mark944T]

Originally Posted by boyt911sc

Mark,

You need a set of pressure gauge to check your fuel pressures (CCP, WCP, & SP). A homemade smoke tester will help you find those hard to find air leaks. A shop with gas analyzer could read measure or check your fuel mixture. Is your WUR -072? Keep us posted.

Tony

I have a service manual so I’ll see what the abbreviations mean and get a pressure gauge. I assume instructions are in the manual. I’ll check YouTube on making a smoker.

What is a WUR? Is -72 the reading and how is it measured?

[pmax]

Lots of good info here

CIS Troubleshooting for Dummies

[Bill Douglas]

A good start is to snip 10mm off the ends of the rubber vacume hoses and refit them. They get a bit loose and the vacume is lost.

With another SC with similar symptoms I opened up the AAV and cleaned it, although it looked already clean, and put it back together. This stopped it's rev fluctuating thing it was doing.

A couple of easy first trys, and good luck.

[boyt911sc]

Originally Posted by mark944T

I have a service manual so I’ll see what the abbreviations mean and get a pressure gauge. I assume instructions are in the manual. I’ll check YouTube on making a smoker.

What is a WUR? Is -72 the reading and how is it measured?

Mark,

Sorry for assuming you are familiar with the common acronyms used in this forum. Don’t worry, we all started like you from the beginning. These are the most common acronyms you will encounter with CIS (constant injection system) discussions in this forum.

AAR (auxiliary air valve)
AAV (auxiliary air valve)
AFS (air flow sensor/switch)
CSV (cold start valve)
DV (deceleration valve)
FD (fuel distributor)
FP (fuel pump)
FV (frequency valve)
CCP (cold control pressure)
RP (residual pressure)
SP (system pressure)
TTS thermotime switch)
TV (thermovalve)
WCP (warm control pressure)
WUR (warm up regulator).
Etc.

Find some reference manuals or books to read about Ketronic system and understand how the system works.
Your WUR should be 0 438 140 072 for USA spec ‘80. -072 is the last 3 digits on your WUR.

Tony

[Bphawk1]

I have an 83 SC with same problem. It appears to be the auxiliary air regulator having the issue.

[mark944T]

Will get on it and thanks for all the info. Didn’t realize these were so complicated. Spent most of my time with older American cars.

[pmax]

Originally Posted by mark944T

Will get on it and thanks for all the info. Didn’t realize these were so complicated. Spent most of my time with older American cars.

Not complicated at all, it's just German

Similar Bosch systems are found in most German makes of that era.

[Rawknees'Turbo]

Mark, here is an old school instructional video about the K-Jetronic/CIS system; it is very helpful with regard to getting to know the various components and what their functions are (and pmax above, better known as pNutz, just luvs the from-VHS transfer skipping ).

[mark944T]

Originally Posted by Rawknees'Turbo

Mark, here is an old school instructional video about the K-Jetronic/CIS system; it is very helpful with regard to getting to know the various components and what their functions are (and pmax above, better known as pNutz, just luvs the from-VHS transfer skipping ).

Thanks!

[mark944T]

Originally Posted by boyt911sc

Mark,

Sorry for assuming you are familiar with common acronyms used in this forum. Don’t worry, we all started like you from the beginning. These are the most common acronyms you will encounter with CIS (constant injection system) discussions in this forum.

AAR (auxiliary air valve)
AAV (auxiliary air valve)
AFS (air flow sensor/switch)
CSV (cold start valve)
DV (deceleration valve)
FD (fuel distributor)
FP (fuel pump)
FV (frequency valve)
CCP (cold control pressure)
RP (residual pressure)
SP (system pressure)
TTS thermotime switch)
TV (thermovalve)
WCP (warm control pressure)
WUR (warm up regulator).
Etc.

Find some reference manuals or books to read about Ketronic system and understand how the system works.
Your WUR should be 0 438 140 072 for USA spec ‘80. -072 is the last 3 digits on your WUR.

Tony

Tony,

What fuel pressure gauge set do you recommend? I see lots of different ones recommended.

Mark

[gerben1986]

Originally Posted by mark944T

Tony,

What fuel pressure gauge set do you recommend? I see lots of different ones recommended.

Mark

Search for a fuel pressure gauge set that's CIS complaint (due to the adapters) or buy one with as much adapters as possible.
I have a Hofman-kit, but that's not for sale anymore.

[Bill Douglas]

Start with the easy, no equipment need either - see post 5

[boyt911sc]

Originally Posted by mark944T

Tony,

What fuel pressure gauge set do you recommend? I see lots of different ones recommended.

Mark

Mark,

I recommend the S&G CIS pressure gauge tool kit. I don’t remember the exact model # because I bought them a long time ago. I have 3 sets by the way. Do not buy the expensive one just pick the basic kit with 12-mm x 1.5 fittings and has the range of 0~100 psi. They usually come with different brass adaptors but you only need one 12-mm x 1.5 male/female adaptor for your control fuel pressure tests.

Tony

[mark944T]

Originally Posted by boyt911sc

Mark,

I recommend the S&G CIS pressure gauge tool kit. I don’t remember the exact model # because I bought them a long time ago. I have 3 sets by the way. Do not buy the expensive one just pick the basic kit with 12-mm x 1.5 fittings and has the range of 0~100 psi. They usually come with different brass adaptors but you only need one 12-mm x 1.5 male/female adaptor for your control fuel pressure tests.

Tony

Thanks again.

[Dave Kost]

Originally Posted by mark944T

I know this has been covered before, but still looking for advice as I think my problem is unique.

I have a 1980SC and it idles up and down rapidly warm or cold. If I don’t give it gas it dies. I took it to a shop (well known) when it only did it when it was cold. Now it does it all the time, cold or warm. Shop doesn’t know why and said they are not at fault for it being worse.

I have some mechanical abilities and want to fix it myself. If I need to buy some special equipment I’m ok with that. Thanks for any advice.

Did it all of a sudden start doing this or was it gradually getting worst? Just started dying all of a sudden or did the rapid idling start first? What did the shop do? Did they try adjusting the 3 mm allen set screw on the metering plate? Sounds like it was worse, after the shop worked on it.

The first thing I would check if the frequency valve is working. The FV relay is located under the passenger seat, If you pull the relay, its a cube, while its running and the idle doesn't change that is your problem.

On 1980, 81, 82 qnd 83's. ALWAYS check if the FV is working first.

Please keep us up dated.

[Paulporsche]

Your symptoms are usually those of a too rich condition. As others have mentioned, you will need to check your fuel and control pressures to help determine this. The WarmUpRegulator is often the culprit causing this. They go out of spec and the bimetal strip inside fails.

Again, per others, vacuum leaks are common and often people richen the mixture too much to make up for them.

Once you post the fuel pressures we can compare them with the spec

[mark944T]

Originally Posted by Dave Kost

Did it all of a sudden start doing this or was it gradually getting worst? Just started dying all of a sudden or did the rapid idling start first? What did the shop do? Did they try adjusting the 3 mm allen set screw on the metering plate? Sounds like it was worse, after the shop worked on it.

The first thing I would check if the frequency valve is working. The FV relay is located under the passenger seat, If you pull the relay, its a cube, while its running and the idle doesn't change that is your problem.

On 1980, 81, 82 qnd 83's. ALWAYS check if the FV is working first.

Please keep us up dated.

BIG NEWS! I started it today and it did the usual of idling fine for about a minute, then started its up and down. I disconnected the FV and it idled NORMAL. BUT, when I revved it up it backfires. I reconnected the FV and it went back to idling up and down.

What does that mean?

[mark944T]

Originally Posted by mark944T

BIG NEWS! I started it today and it did the usual of idling fine for about a minute, then started its up and down. I disconnected the FV and it idled NORMAL. BUT, when I revved it up it backfires. I reconnected the FV and it went back to idling up and down.

What does that mean?

I guess I read your comment wrong. So this means my FV is fine. On to looking for vacuum leaks I guess. Thinking of getting this.

https://www.ebay.com/p/EVAP-Smoke-Machine-Diagnostic-Emissions-Vacuum-Leak-Detection-Tester/689245513

Also buying the S&G 338000 CIS fuel injection tester. Has the correct fittings according to Tony. Will check my WUR because my car does run rich. Wouldn't pass smog here in California. I have a Bentley Porsche SC service manual but don't see info on the WUR. Where is it?
Will post results.