Strange Idle Oscilation-Lost Sync Code 97

[subatoy71]

Having some issues with idle recently. The only thing I can point to is that I added A/c circuit to what was a very stable running setup. The input trigger is 12v in on nitrous and output is FIDLE. My idle control is running as open loop, 2-wire mode and inverted. I cannot say that I was able to get any increase in idle speed despite what values I and I am not sure if its working with the valve in inverted mode.

Of greater concern to me now is that when the engine starts cold e.g first time for the day after overnighting it idles at 1500 rpm and starts oscillating. Throttle input delivers a steady,cyclic miss like low rpm launch control. It will do this for a few minutes then clears to a steady 1500 rpm. It appears to be stuck there unless I switch on the a/c and immediately switch it off again. That seems to settle it and all is back to normal PW operation @ 1000 rpm. Tried one straight value across all temps as well, no difference

If the engine is switched off and restarted there is no oscillation but idles at 1500rpm again and I have to cycle the A/C sw again to bring it back to normal. The engine runs like a champ to 8000rpm thereafter, no missing.

Note that if the oscillation is present the A/C output does not work but once it ceases A/C works, no problem. This behaviour has been 100% repeatable as I have observed it over the last week or so. Also the engine starts easily hot or cold despite this.

Further to that fate had me engage the clutch to see if map load had any influence- the car rolls out on the fast idle, throttle input responds normally, no missing. I back off the throttle, disengage the clutch, the engine idles at the 1500 rpm, no oscillation and I cycle the A/C sw and idle is back to normal.

What is baffling to me is that the datalog I pulled is showing lost sync, reason code 97(see attached). The lost sync counts ascend in value at each oscillation. It is definitely not the cam sensor here.

Can anybody explain whats happening?

2016-11-20_20.50.30.msl

[Matt Cramer]

The loss of sync is causing the oscillation and other weirdness. What sort of sensor inputs are you using for RPM? Can you post your MSQ? Some setups are better to troubleshoot with a tooth log and others with a composite log, but we'll need to take a look at the crank and cam signals.

[subatoy71]

OK. I will pull a composite log later tonight but I need to wait at least 4 hours to get it to oscillate again; just used the car.

In the meantime I have attached the msq. It is likely I would have done some offline editing but only to tweak ignition and fuel tables, nothing else.

Idle Oscillation 30112016.msq

[subatoy71]

No luck with the log. I will have to leave it overnight as it always oscillates first start in the morning and in the evening after work.

[Matt Cramer]

What type of crank / cam sensors are you using? VR or Hall effect?

[subatoy71]

Cam and crank sensors are VR.
Got the composite log this morning(see attached). It does show a miss on the cam trigger.
But....
Why does it "appear" to be coolant temperature sensitive?
What causes the idle to run so high when there is no sync issue occuring?
PWM duty is way off spec though idle control is open loop and hi-idle continues long after crank to run taper time.
Why does the bad idle PWM duty correct itself when the A/C circuit is cycled?
Would it be agood idea to re-load the firmware at this point?

2016-12-01_07.06.57.csv

[Matt Cramer]

It seems to be an extra pulse on the cam sensor. VR sensors are temperature dependent themselves. You might need to adjust the MS3X trim pots.

When it loses sync, the engine will often go into afterstart enrichment, the closed loop idle can "lose its place", and a number of other things will happen that can cause idle oscillation.

[subatoy71]

OK I gave R11 on the MS3X card one half turn clockwise and tried a cold start-No more oscillation.
Thanks Matt

I am still left with the high idle idle issue though. Still need to cycle the A/C on and off to normalize the idle PWM duty See attached log). I will set Cranking duty and warm up idle duty to identical figures to eliminate ramp issues and see if that makes a difference.

High Idle.png

Also can anyone confirm that the A/C idle up feature is working on idle valves in inverted mode?

[Matt Cramer]

Please post the full log and your latest MSQ to give more data on the idle settings.

[subatoy71]

MSQ was posted in the first or second thread, log too

[Matt Cramer]

Is the log from that post the same one you posted the screen shot of? If not, please post the log the picture came from.

[subatoy71]

Here it is.

2016-12-08_19.29.49.msl

2016-12-08_19.29.49.msl

[Matt Cramer]

Try a shorter crank to run taper time and less timing in the 1400 RPM, under 40 kPa range.

[subatoy71]

Tried fixed timing at 10 degrees and 0 for crank to run taper-No difference.
I will try a lower frequency and see what happens.