Strange Idle Issue - CIS problem?
 

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? :confused: 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..

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

this is your THIRD thread on this subject

http://forums.pelicanparts.com/porsche-911-technical-forum/960574-strange-idle-issue-possible-cis-problem.html

http://forums.pelicanparts.com/porsche-911-technical-forum/960639-strange-idle-issue-cis-problem-posted-someone-else.html

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 .

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

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 .

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.

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.

I will do this first - and report back shortly.

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

Welcome to the forum........
 

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

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

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

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.

Erratic cold idle........
 

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

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

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.

Give him some slack.......
 

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

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.

Cold start.........
 

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

Thanks Tony.

I do have a issue when starting the engine first time - but what irritates me is the second time I start it and the preceding idle that takes place. (to be clear it always starts and starts wonderfully after warming up) - just the idle..

What is the spec for the 090 WUR resistance - Ive read conflicting accounts of this range?

Also - Control Pressures were given in my #16 posting..

Alright – made some more headway in the diagnosis. :)

First start of the morning went off without a hitch and fired right up – began idling at 900 or so rpms.

I then pulled the FV relay and the engine immediately began to oscillate and sputter and miss – plugged it back in and the idle smoothed out to 900.
I kind of expected this as everything must be working properly to make a smooth idle..

SO

I strapped the gauge set on the engine and went for a spin around town and out to the country and back – maybe 20 minutes of driving time. Running beautifully, it reminded me of my original test drive..

Wanting to mimic my idle issue after restart, I shut the car off and went in and answered a couple of emails – 7 minutes later I started the car (easily started) and right on cue, the idle was now oscillating and running rough. I then reached down and pulled the FV relay and there was no change in idle– still running rough.. When I plugged the relay back in – it smoothed out to 900 (almost instantly) - and stayed that way..

See video here of the whole ordeal: https://youtu.be/LHgDRiHIS6Q

So it looks like I need to focus on the Lamda relay, ECU, and FV system… I am going to clean the contact points and (as Dave K suggests) order a new relay (once I figure out which one is the correct one to order).

One little nagging issue is why is the issue so predictable. :confused: i.e. running great for the first time, but then crappy after the engine has been running and second start. Normally bad relays / bad connections aren’t predictable.. Is there a “reset” function in the ECU that maybe is malfunctioning - why did the action of plugging back in the relay fix my problem...??

My thoughts are if the Lambda circuit is compromised after heat rears it's head, you may have a frequency valve that is not functioning when hot.

Deal is, when idling like yours in the lumpy stage, if the Lambda/O2 circuit is interrupted, it will backfire when revved, not when throttle is backed off.

Here is a vid made several years ago where I killed the feed to the frequency valve. May not be your problem but a simple check is when running lumpy, pull the O2 fuse. That will do the same thing as me pulling the relay. If no change in function, maybe?

<iframe width="560" height="315" src="https://www.youtube.com/embed/5tdpCYyvqSc?ecver=1" frameborder="0" allowfullscreen></iframe>

LOL - I completely missed your post before my minutes old recent post. You are on your way to nailing this. Good work.

I can walk you through the back end as well as 50 others here, Broseph.

"One little nagging issue is why is the issue so predictable. i.e. running great for the first time, but then crappy after the engine has been running and second start. Normally bad relays / bad connections aren’t predictable.. Is there a “reset” function in the ECU that maybe is malfunctioning - why did the action of plugging back in the relay fix my problem...??'

36 year old car that has not been run much lately
Bad/corroded connectors, connections (old)....
Solder joins fail in the ECU, O2 relay....
Frayed, fretted wires....
Rubber parts that have hardened cracked.....
Leaking vacuum hoses....
Ethanol gas that destroys rubber- Bet the Porsche Engineers did plan for that. And I bet they didn't take that into play when they spec'ed out the fuel pressures with Ethanol Gas.
Hit a bump and things get knacked up and jarred loose.

These ain't Toyotas!

Yep. I say simply a tired relay (or minor corrosion) which high life found. Hat is off to him.

There is one anomaly identified in a post many years ago where the 12 pin connection on the big bar cross member between the two shocks was corroded and the the link from Lambda box to freq valve was interrupted - only when blisteringly hot, though. Atlanta car.

check the relay for bad solder joints or replace the relay, I would go for the solder joints,.

next time try unplugging the connector on the FV first.

if that does not do it check solder joints

Get a can of this stuff. Great for removing corrosion.

http://forums.pelicanparts.com/uploa...1498480000.jpg

As Bob mentioned there is a 12-pin connection in the engine bay. That's the connection from the engine sensors to the lambda box under the passenger seat. Can be hard to get to if you have the heater blower. It's on the back left side near the cruise servo mounted on the firewall. The Deoxit spray and a small wire brush or emory file is good for removing corrosion. Also it's a good idea to take a razor blade and spread the pins. Look at the pin up close and you'll see what I mean. Dennis always suggests that and for good reason.

Spring for a new OXS relay (or two - always good to have a spare in the glove box) but it never hurts to give all the connections a good cleaning.

Time to update........
 

Tim,

It would be time to update some terminology in your "CIS dummies" thread. There is no such thing as OXS relay. The said relay is for the frequency valve. A bad relay causes the FV to be inoperative and has no effect on the OXS itself. Just my two-cents.

Tony

i looked up the 81 and 82 diagram
the diagram has a relay called the OXS relay that provides power to:
the OXS control
acceleration enrichment
frequency valve

all power comes from fuse 18.

you might try spinning and/or cleaning the contacts for fuse 18

Thanks Tim for that - I ordered a can from eBay. I am going to go through the different connectors and clean and spray as many connectors as I can. Ill look for the 12pin connector first..

I ordered a BOSCH 0 332 019 150 from our forum sponsor.. From what I read it is the Bosch number for the relay in question - (i.e. VW/Audi 821 951 253 or PCG-951-253-00 Porsche).

Tony, unfortunately the way the Pelican forum software works you can't go back and edit posts after a certain age. I don't know how old but I can't edit the posts in that thread anymore. Maybe some admin or moderator can change the setting for me.

Anyway, we've had this conversation before. I think we all understand the relay controls the frequency valve but it is labeled OXS relay in places like the Bentley wiring diagrams. Right or wrong, the name seems to have become part of the common lexicon.

I have something similar going on- Today mechanic checked fuel pressure, and when we turned the car off the pressure bled within just 2-3 mins almost down to nothing- he is installing a new fuel accumulator in my car..not sure this will help you or even solve my issue but hey , its a thought.

Please update us in this thread when you find a solution

Fuel accumulator test......
 

Tarek,

How did your mechanic come to the conclusion that the fuel accumulator was the culprit for the residual pressure loss? Did he test the fuel accumulator? What happens next if after replacing the fuel accumulator the problem still exists? Replace another CIS component until the problem is fixed?

Tony

He said if we lose pressure its gotta be fuel accumulator because its original..it could be something else? aaaakh

Fuel accumulator........
 

Tarek,

Let's hope the mechanic was lucky in guessing the culprit. Without testing the fuel accumulator he was hoping it was the culprit. There are three (3) commonly known CIS parts that could cause fuel residual pressure loss. Keep your fingers crossed.

Tony

to Iowa...did you mechanic check your system with the gauges ? I am surprised that none has mention that your fuel pump check valve could also be your culprit on loosing the fuel system pressure...then again in this post are to problems or?

Ivan