Just reinstalled my new engine before musr12. Its a 2056 with Raby 9550 cam and djet. I reinstalled the original FI system complete. Components were bench tested before being reinstalled. Car runs beyond my expections.

Heres the only problem I have really have. Upon cold start (not cold-cold start) it idles very low and rough. A few minutes of throttle held to about 1400 rpms, and the aar kicks in and everything is normal from there. Or, if I start it and pull it out of the garage to the drive, everything is normal. Aar is working properly. Head temp sensor is the correct one and ohms are within specs both hot and cold. Ts-1 also shows 310 ohms at 60 degrees. Cold start valve is not hooked up. I have considered a leaky injector, but is seems that would cause problems only when there is adquate fuel pressure, not after setting all night. Ambient temp seems to make no difference.

Opinions please.

D-Jetronic Idle Stability (from Brad's site)


...........
"About an hour later, you need to make a 30 minute errand to go to the Post Office. You start the car, the idle comes to the setpoint or somewhat below, quickly. That's because the AAR is still hot and isn't open, and while the motor is warm, the heads have cooled considerably. Because the air-cooled D-Jetronic depends on head temp for setting the warm-up mixture, you're likely to have a bit of bogging and low idle for the first 5 minutes, until head temperatures come up. This is a well-known design issue with 914's, "warm start over-enrichment" is what we'll call it. There's not too much you can do about it. You may have to use an open throttle to get the car to start, as it's too rich and needs more air."

could this be your condition?

Thanks Ray, but that isn't the symptom . This only happens at cold start. both block and head are at ambient temps.

ooh....didn't understand the "Upon cold start (not cold-cold start)".
thought you were already out driving for a while, and it was just semi-cold.

No prob, Ray. Cold-cold start refers to temps under freezing. I actually got that term from Brads site. LOL

you say when the AAR valve kicks in; do you mean when it closes? (too lean when it is open?)
Was the MPS adjusted for the increased displacement and the 9550? I've got my idle set to about 1100rpm per Geoff's suggestion after he tweaked my MPS.
Do you have the idle knob on the ECU? Try playing with it.

AAR works as designed. It opens fully cold and closes after 5 or so minutes. Mps has been adjusted and co has been set by a Porsche mech and Bosch certified technician who knows his stuff.

That is my guess....you may be too lean at idle.

You didn't say if you checked the fuel pressure or not?

Also, check your AFR with a meter at load-and no load.

D-Jet Guys,

I had the same problem with my Raby #9550 cam, etc upon startup. I adjusted the ECU to get it corrected. Now I can't remember which way I turned the knob. Can someone tell me which way is lean & rich??? clockwise or counter clock??
I forgot??
Tom

I took the car to local Bosch factory trained pcar mechanic. He put it on his machine, checked fuel pressure, set tps, checked dwell and timing (they were spot on), adjusted mps for the added displacement, and set afr.

Clockwise richens - but you'll be changing the fuel delivery during idle for both cold and warm engine operation (your warm idle may get worse). Along those lines, if your mechanic set the ECU knob for emissions for warm idle, I wouldn't want to change the setting.

Out of curiousity, how does it cold idle if you block the AAR (plug the intake hose to the AAR or temporarily clamp it closed)? Maybe you can just take it out of the equation all together.

The aar has been taken out of the picture with no change. It functions properly. its only the very first few minutes of cold startup.

most likely too rich at idle.
Turn down the knob on the ECU.

I am curious how your trained bosch mechanic adjusted the MPS for the new displacement....
Dyno tuned or did he put in an O2 sensor to get it set properly while driving?
It cant be done without a load.

Not trying to be sarcastic, but just turning the screw till it runs right is not how that part needs to be tuned and modified.

I would suggest a simple test would be to put an O2 sensor up the tailpipe and see what the mixture is when the problem is occuring...that will lead you to the proper place to fix it.


Rich

Rich, running rich is my thought too. Yes an o2 sensor was used. I did turn the ecu knob to full lean, and it made a small improvement but did not cure the problem.

MPS needs to be set under load...even with an O2 sensor.
Its a guess otherwise...and you would be shocked at how small of a turn makes such a huge difference.

I drive them while tuning...I dont have a bench setup, I use an A/F meter, O2 sensor and seat time.
It takes about 20-30 minutes to get it perfect.
Start cold...then as you drive you need to keep tuning.
After that, I start one more time the next morning to verify the "new" cold setting still works.

If you are all ok with how it runs everywhere else, put in a varialbe POT on the ambient air sensor and re-connect your cold start injector.
Turn the POT up till the injector flows when you have your specific problem....that might help.
From there you can measure the POT to see what value of resistor you need to trick it.

OR, use a VW 411 mps and your problems will go away.
Its a single diaphram and much easier to get right all across the range.

For me, I start it and get in and drive it to the store...any temps.
When I get there, it idles perfectly...a 10 minute drive.
Air cooled cars properly tuned for running temps tends to run like crap when cold...

Rich

Not sure of the cause nor cure Curt, but you'll want that cold start injector hooked up for when it turns cold back there.

Enjoyed our chat & breakfast last week, & will touch base next time I'm back in OK, which unfortunately won't be for a few months as it stands now.

Best!
Tom
///////

My stock engine does the exact same thing. My AAR also works as it should. In my case mixture is over rich for the first couple minutes. It will smooth out if I lean the ECU knob, but will lean surge once up to normal operating temp. It is a balancing act I just learned to live with. I suspect the resistance curve of the head sensor just is not ideal. I am still amazed these old analog open loop systems work as well as they do ! Still getting 30 MPG with my 2.0

Its too rich at startup due to the 9550 cam. 1100 idle rpm will help clean it up. Set the ECU knob to full lean counterclockwise.

Its a small sacrifice when you now have 115-120 hp...