Strange Idle Issue - CIS problem?

[High Life]

Originally Posted by 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

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..

[High Life]

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. 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...??

[Bob Kontak]

Originally Posted by High Life

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.

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?

[Bob Kontak]

Originally Posted by High Life

So it looks like I need to focus on the Lamda relay, ECU, and FV system

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.

[Dave Kost]

"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!

[Bob Kontak]

Originally Posted by Dave Kost

Normally bad relays / bad connections aren’t predictable.

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.

[T77911S]

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

[tirwin]

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



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.

[boyt911sc]

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

[T77911S]

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

[High Life]

Originally Posted by tirwin

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



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.

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).

[tirwin]

Originally Posted by boyt911sc

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

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.

[Tarek307]

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

[boyt911sc]

Originally Posted by Tarek307

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

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

[Tarek307]

Originally Posted by boyt911sc

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

[boyt911sc]

Originally Posted by Tarek307

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

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

[proporsche]

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