Strange Idle Issue - CIS problem?

[High Life]

Second attempt to get this posted on the forum..

Hello - Brand new Porsche owner here.

Background:

I recently purchased a 1981 Porsche 911SC with 78,000 miles. It has decent documentation - 3rd owner - Ive driven the car roughly 300 miles

Motor was out for a rebuild at 70,000 miles in 2005 (12 years ago)
There were many things replaced (Long list) - but from the CIS main components the following were replaced:

O2 sensor
Fuel pump
Rebuilt Fuel Distributor head
Remanufacutred Warm up regulator (WUR Model 0438140090)


Situation:
I am having difficulty diagnosing a rough idle situation.

The car will cold start with foot pedal half way to floor holding for 30 seconds or so to smooth out idle (a little rough to start) - but then the car runs phenomenal.. 900 revs at idle (dead straight) and can drive for hours. I have taken 4 long trips with one lasting 2 1/2 hours with no idling problems or performance issues..

However - Once I shut the vehicle off and try to restart - the car runs horrible. It will start with no problems - but will not idle. It will oscillate ("hunt" or "lope") up and down around 500 to 700 rpms and performance will suffer - I have little backfires or sputtering that happens upon acceleration. Its still drivable - as I drove it 30 minutes to get home after a car show this way - however it doesn't correct itself - it ran rough and idled rough the entire way.

If I leave the car overnight - It will start and idle at the 900rpm range - running like the car I imagined.. BUT shut it down to fill up with gas - then it runs like crap..


Any suggestions to the components I should test or change? Im not sure where to start - and this issue severely diminishes the use of this car..



I have searched and read through many threads (so I am working on educating myself) - I ordered a CIS fuel pressure tester and I can use a multimeter. I also have the Bentley manual. The CIS system is all new to me - so I made need some step by step help in performing the tests..

[Dmitry at Pelican Parts]

Welcome and congrats on the new ride! I'm attaching a link to our site's DIY tech articles on our platform. It's a great guide if you're going to be doing the maintenance and any fixes down the line. If you need more details on a procedure, feel free to post a Comment just below the article and one of our techs will provide you with more specifics. Please let us know if you have any questions!

Porsche 911 (1965-1989) Technical Articles - Pelican Parts

[T77911S]

this is your THIRD thread on this subject

Strange Idle Issue - Possible CIS problem?

Strange Idle issue - CIS Problem? (posted for someone else)

[theiceman]

Originally Posted by T77911S

this is your THIRD thread on this subject

Strange Idle Issue - Possible CIS problem?

Strange Idle issue - CIS Problem? (posted for someone else)

cut him a little slack .. when I first started here I did not realize the forum moved so fast . When I posted something I thought it got deleted when in fact it had simply been buried three pages back when I checked a day later. This place takes a little getting used to .

[proporsche]

Hi Iowa...you are at the right start..get those fuel press.gauges.Install them and then let us l know the reading .
1.when cold
2.when warm.
3.after restart.
Do not worry you can drive the car with the gauges in the car.

Possibly your wur is acting up..it is actually very easy to fix once you know the numbers.
Also your fuel pump check valve could be the culprit and you fuel accumulator. But start with installing the gauges into the fuel system..make sure you have it in the correct -direction-way

Ivan

[Dave Kost]

The first thing to check in these Lambda 911 SC's is if the frequency valve is working.

The ECU and Frequency Valve relay, under the passenger seat controls the FV. Get the car running and pull the relay under the passenger seat. If the engine idle does not change the FV is not working.

Therefore, its the relay, ECU or in some cases the wiring is bad.

This has happened to me twice, so keep a spare relay handy. If, the car sits outside in the rain and you have a leak you can ruin/corrode the ECU and/or relay. The water will pool up under the seat. Seems to happen more to targas and convertibles.

I would start here while you wait for the CIS gauges .

[High Life]

First off - I apologize for the second posting - I submitted the first on Sat and then the second on Sunday to no avail (they were not accepted by the moderator) the 3rd posting is because I asked another forum member to submit a post as I am working through the running issue.

It is not my fault that I had to wait for moderators to approve my postings. My second attempt and third attempt (by another user) was to get my question on to the forum. There is nothing in the FAQ that stated I could not post in the tech forum once I registered.

As far as the forum platform - I am a member of bimmerforums (same platform) for 12 years and have no troubles posting - so I was completely confused when I was able to post in one section (off topic) but not in this section (again nothing in the FAQ sections states I cannot post once registered). Please see my original plea for forum help here: http://forums.pelicanparts.com/off-topic-discussions/960631-help-i-cannot-post-new-topic-tech-forum.html

If you still don't understand that the 2 posting were outside my control - feel free to PM me and I will work you through the logic of the forum error.


Moving forward. If it is possible to delete the other 2 threads - I would be happy to - but it looks like i cannot. Hopefully this wont be too confusing for the majority of the users ( I know some will still struggle) and again I apologize to those who do.

[High Life]

Originally Posted by proporsche

Hi Iowa...you are at the right start..get those fuel press.gauges.Install them and then let us l know the reading .
1.when cold
2.when warm.
3.after restart.
Do not worry you can drive the car with the gauges in the car.

Possibly your wur is acting up..it is actually very easy to fix once you know the numbers.
Also your fuel pump check valve could be the culprit and you fuel accumulator. But start with installing the gauges into the fuel system..make sure you have it in the correct -direction-way

Ivan

I received my CIS Pressure testor and will work on this and get the readings posted onto this thread - I will follow "CIS for Dummies" posted on this site.

[High Life]

Originally Posted by Dave Kost

The first thing to check in these Lambda 911 SC's is if the frequency valve is working.

The ECU and Frequency Valve relay, under the passenger seat controls the FV. Get the car running and pull the relay under the passenger seat. If the engine idle does not change the FV is not working.

Therefore, its the relay, ECU or in some cases the wiring is bad.

This has happened to me twice, so keep a spare relay handy. If, the car sits outside in the rain and you have a leak you can ruin/corrode the ECU and/or relay. The water will pool up under the seat. Seems to happen more to targas and convertibles.

I would start here while you wait for the CIS gauges .

I will do this first - and report back shortly.

[High Life]

Just to help diagnose

Video of original running with no issue:

https://www.youtube.com/watch?v=9dQfq41RSLw

Video after the long drive and running perfectly..

https://www.youtube.com/watch?v=s_V2NE8giFg

[boyt911sc]

HL,

Get familiriarize how to use and install the CIS pressure gauge correctly. Measure the control (cold and warm) fuel pressure and system fuel pressure. Learn to do the test using the FP without running the engine. If you are not familiar with this procedure, simply ask and there are many guys in this Forum to help. Hope you did not buy the HF brand pressure gauge.

What is the Bosch ID number on your WUR? Measure the heater resistance (Ohms) when the engine is cold. Keep us posted.

Tony

[Bob Kontak]

Originally Posted by High Life

Video after the long drive and running perfectly..

What happens in the lumpy state if you rev it up?

[High Life]

Originally Posted by boyt911sc

HL,

Get familiriarize how to use and install the CIS pressure gauge correctly. Measure the control (cold and warm) fuel pressure and system fuel pressure. Learn to do the test using the FP without running the engine. If you are not familiar with this procedure, simply ask and there are many guys in this Forum to help. Hope you did not buy the HF brand pressure gauge.

What is the Bosch ID number on your WUR? Measure the heater resistance (Ohms) when the engine is cold. Keep us posted.

Tony

Hello Tony - Ive read quite a few of your postings.

I purchased Tool AID CIS K-Jetronic tester 33800 C.I.S. K-Jetronic Fuel Injection Tester | Tool Aid

I had seen that use Ossiblue recommended them in a couple of threads.

I am reading through the CIS for Dummies posting again and will report the tests as I get them finished.. I need to fabricate a fuel pump switch to perform the cold - I will run into the auto parts store next.

I found the Freq Valve relay - will test (as suggested by Dave) right after I get the cold readings - since I have to start the car.

Info:
1981 Porsche 911SC
Engine number 6410817 (81 3.0)

BOSCH WUR Model is 0438140090
In testing the Ohms of the WUR - I am getting 11.9 and the current temp is 78-80 F

[High Life]

Originally Posted by Bob Kontak

What happens in the lumpy state if you rev it up?

It will rev up - I can hear little popping / sputtering when I let off

I have drove it in the poor idle condition a few times and all three times the performance was diminished on the road traveling at speed - it seemed like I didn't have the pickup and idle still remained poor after driving for 15 minutes to 30 minutes.

[boyt911sc]

HL,

You will always have an erratic cold idle because of your WUR-090 unless it is corrected. There are several things you have to check and test namely:

Fuel pressures (cold, warm, and system).
Integrity of the vacuum system.
Ignition and valve timing.

When you perform your fuel pressure test, do it with just the fuel pump running. No need to run the engine. Just make sure you have a fully charged battery. Record the fuel pressure reading at 30 sec. intervals up to 5 mins. (max.). Do not attempt to tinker or alter the fuel mixture setting at this point. You would have plenty of time to do it later. Keep us posted.

Tony

[High Life]

Ok here are the Test Results (Following the CIS troubleshooting for Dummies thread)
The engine sat for 24 hours and was never started – so it was cold for all the following tests:

WUR Ohms (rechecked and with temp gun) 10.5 Ohms - temp 80F or 27C
System Pressure (Valve to WUR closed – fuel pump on – WUR unplugged) – 4.8 bar
Cold Control Pressure (Valve to WUR open – fuel pump on – WUR unplugged) – 1.9 bar
Warm Control Pressure (Valve to WUR open – fuel pump on – WUR plugged in) – 3.8 bar after 1m20sec – stayed at this level for 2 minutes.
Residual Pressure (Valve to WUR open – pump off – WUR plugged in) 5 min 2.2 bar, 15 min 1.8 bar, 30 min 1.7 bar, 60 min 1.6 bar, 120 min 1.6 bar

Videos
setup: https://youtu.be/T1mXyPeAkKI
system pressure: https://youtu.be/ltWamnN77IM
cold control pressure test: https://youtu.be/A6G6h9uVDyY
warm control pressure test: https://youtu.be/d87_qHkN2QE

[T77911S]

Originally Posted by theiceman

cut him a little slack .. when I first started here I did not realize the forum moved so fast . When I posted something I thought it got deleted when in fact it had simply been buried three pages back when I checked a day later. This place takes a little getting used to .

this is the problem with the younger people today.
I let him know he did something wrong, nicely, and now you have someone telling me to "cut him some slack".
notice I told him he already had 2 posts going, then he did this one.
its like the "sub'd" posts people do. if you don't tell them there is the thread tools option for subscribing to a thread, great threads get cluttered up with "sub'd"

he can also go back and delete the his post and ask his friend to delete the post he started.

[boyt911sc]

Originally Posted by T77911S

notice I told him he already had 2 posts going, then he did this one.

Ty,

He is new in the forum. Offer him some help or ignore his thread. I think he is trying to annoy you to get back to you (joke). The hot and humid weather must be getting on your nerve these days (another joke). There are other more important things in life than Porsche 911. Take good care my friend.

Tony

[High Life]

Originally Posted by boyt911sc

HL,

You will always have an erratic cold idle because of your WUR-090 unless it is corrected. There are several things you have to check and test namely:

Fuel pressures (cold, warm, and system).
Integrity of the vacuum system.
Ignition and valve timing.

When you perform your fuel pressure test, do it with just the fuel pump running. No need to run the engine. Just make sure you have a fully charged battery. Record the fuel pressure reading at 30 sec. intervals up to 5 mins. (max.). Do not attempt to tinker or alter the fuel mixture setting at this point. You would have plenty of time to do it later. Keep us posted.

Tony

Tony,

Can you explain what you mean by erratic cold idle? The car runs beautifully when first started cold - runs for hours and idles flawlessly (see video).

Shut it off then restart when warm is where I run into problems.

[boyt911sc]

In your post #1, you mentioned that you had to step on the gas pedal during a cold start. This is an obvious sign of trouble. The car/engine should start unassisted. Could you start the engine without additional help?

Second, the WUR's heater resistance is out of spec. and this will cause a premature LEAN condition during a cold start. Go ahead and measure your control fuel pressures. Share these data with us and I will explain to you the problem. Keep us posted.

Tony