Chasing CIS cold and warm start idle issues

[dugr]

I’m chasing a CIS idle issues with my 1981 911SC.

It consistently starts cold and idles at 950rpm. As the WUR warms up and AAR starts to close the idle drops to about 650rpm and eventually getting back up to 950rpm as it gets to temp.

With the engine at temp, if I shut it down and do a restart within 5-10 seconds, the idle consistently drops down a 100-150 rpm, over a period of a couple of minutes, it slowly rises back to 950.

If I let it sit for 10 minutes or more, on restarts, the idle is down to 500-600 rpm and often chugging.

In the situations above, once the engine is running, the only moving components are the mass air sensor, FV, and the FD. The mass air sensor is clean and has absolutely no stickiness to it. With the engine at temp, on a 70° day, the WCP doesn’t drop even after an hour.

I acquired this SC about a year ago, it had sat for almost 10 years and has approximately 65,000 miles on the clock. It was hard starting so I replaced the accumulator but, since I've owned it, the CIS has never been quite right. I removed the components and tested the airbox for leaks, r/r all the rubber components.
I've chased down and remedied all the other known issues.

Prior to this post, I perform a thorough smoke test at injector port #4 with the engine on BTDC. I did several smoke tests to make sure I wasn't missing anything and found no leaks in the system.

With Tony’s help, everything has been tested in and out of the car. I've performed cold start-ups tests, bringing the engine up to temp, removing the AAR, AAV, and DV one at a time until all were out of the circuit and the lines plugged, all with no changes. Performed warm start tests in the same manor, all with no changes.

Pulled vacuum tests on all the ancillary components, brake booster, cruise, distributor vacuum advance/retard, etc..., and found no issues. Tested the 15C TS and the 35C TS in and out of circuit along with bench testing, found no issues.

Timing is spot on and not iractic. Pulled vacuum on advance and retard with timing light connected and all operated smoothly.

With the engine at full operating temperature @950 rpm, with a dwell meter connected it's hovering at 45° with a swing of +/- 2°.

1. Year of engine: 1981
2. US or RoW (Rest of World): US
3. WUR model number: 090 "Tony-Calibrated"
4. FD model number: 0 438 100 077
5. Ambient temperature at time of test (in degrees C): 23.1°c/72.f
6. WUR Resistance: 25.7 Ohms
7. System Pressure: 4.96bar/72psi
8. CCP: 1.93bar/28psi
9. WCP: 3.58 bar/52psi
10. Time delta for Cold -> WCP (in minutes & seconds): 3:10
11. Residual Pressure @ 5 min: 2.8bar/40psi
12. Residual Pressure @ 15 min: 2.2bar/32psi
13. Residual Pressure @ 30 min: 1.7bar/24psi
14. Residual Pressure @ 60 min: 1.6bar/23psi

Components replace:
Fuel Tank Filter
Fuel Filter
Accumulator
Injectors
Injector Sleeves and O-rings
WUR
O2 Sensor
Fuel Pump Relay
Enrichment Relay
Sparkplugs
Rotor & Cap

Tested:
The 15C TS was open at room temperature, once in the refrigerator it closed.
The 35C TS was open at room temperature, once the engine is started, within 3 minutes it closes.

Disassembled, cleaned, and tested AAR.

Tested by Tony:
FD
CSV
Injectors

Tony said the FD was in excellent condition. That said, at this point only thing I see left is to rebuild the FD.

Any insights would be appreciated.

Doug

[mike sampsel]

Have you measured the CP at the WUR when the idle is 100-150 rpm? And the 650 rpm?

Just thinking out load.

All your other numbers beat the crud out of mine!
I had a drop off in rpm once when I came to a stop and put in the clutch, I was too lean I think. A wideband sensor to measure your AFR is nice to have. If you don’t have th gauge setting the proper enrichment setting is voodoo art (LOL).

[mike sampsel]

You might run a couple of tanks of gas through with sea foam before rebuilding the FD.

[dugr]

Originally Posted by mike sampsel

Have you measured the CP at the WUR when the idle is 100-150 rpm? And the 650 rpm?

Just thinking out load.

All your other numbers beat the crud out of mine!
I had a drop off in rpm once when I came to a stop and put in the clutch, I was too lean I think. A wideband sensor to measure your AFR is nice to have. If you don’t have th gauge setting the proper enrichment setting is voodoo art (LOL).

Yes, WCP is always the same 52psi after it's warm.

[dugr]

Originally Posted by mike sampsel

You might run a couple of tanks of gas through with sea foam before rebuilding the FD.

I've considered dumping a gallon of Techron in it when I'm down to a quarter tank (and not refilling the tank) to see if there's "Magic in a Bottle!"

The conditions are consitant as I decribed. When everything else has been tested remedied and/or removed from the circuit, it really gets down to (in my mind) the FD.

BTW: Tony has been a unbelievable help through this whole process. All the information that I provided earlier was because of Tony. He has had me test... measure... test... measure... test... measure... again! He's like a CIS drill instructor!>) I can't thank him enough... Though, I have to admit I wasn't saying thankful or kind words when I was reinstalling the CSV with only a partial engine drop. My back will never be the same.

[mike sampsel]

So if you measure the fuel from the injectors around the time of the 100-150, via fuel in baby bottles, this might yield a clue. Throwing spaghetti at the wall, I am. I've not done this but it does not seem so hard to me.

It might point to the FD?

[dugr]

That would be a tad difficult to do, I have steel lines. Pulling the injectors while the engine is hot and testing sounds like a recipe for disaster. But, that could eliminate my issue with idle... “CABOOM!”

[mike sampsel]

Well I guess I'm lucky without the metal fuel lines, or unlucky.

Still seems odd that the resident CIS expert said your FD is in excellent condition, Rebuilding it does not seem to make sense.

Since the car sat for 10 years, have you drained and cleaned the fuel tank?

Again, I'm not an expert, but I've seen what gummy goo gets inside a tank of old fuel. It's not pretty.

[dugr]

Yes, The first item under componets replaced, the Fuel Tank Filter. The tank is clean.

As Tony said to me... "We're missing something, it has be right under our nose" I told him... "I have a big nose!"

All kidding aside, I'm hopeful someone on the forum will respond whom may have had these same issues and can offer up a solution. I don't have an issue rebuilding the FD or having it done. I just don't want it to be an exercise in futility.

[Funracer]

Originally Posted by dugr

Yes, The first item under componets replaced, the Fuel Tank Filter. The tank is clean.

As Tony said to me... "We're missing something, it has be right under our nose" I told him... "I have a big nose!"

All kidding aside, I'm hopeful someone on the forum will respond whom may have had these same issues and can offer up a solution. I don't have an issue rebuilding the FD or having it done. I just don't want it to be an exercise in futility.

Did you ever get this figured out?

[Alfasrule]

Don't know much about Porschezz. In ALFA land this type of issue is usually caused by the oil breather and the circulation system. It gets plugged. Constipated. Does this car have such a system that is similar? Just a thought!

[dugr]

Originally Posted by Funracer

Did you ever get this figured out?

Yeah... It was right under my nose.

My issue was the dwell meter out of calibration, leading me to set the mixture extremely lean.

The final clue was when I set it up to run open-loop, it ran great so I left it alone for a few days. When decided to reattached the OXS the meter was reading in the low 30°. I decided to get an inexpensive scope that attaches to my laptop and hooked it to the test port, I was nearly spot on and just needed a little fine tweaking. The nice thing about using a scope is it makes it easier to test the functions of the ECU and ancillary components.

Of course, I find this out after I testing, retesting, replacing, and rebuilding almost all of the CIS components. Tony was almost as frustrated as I was. I now know more about CIS than I've ever wanted.

Doug