Intermittent Rough Running Diagnosis

[tony-baroni]

Okay here's another update. It's idling high, around 1900. The TPS voltage with throttle closed is 0.6V. The TBI is whistling very loudly, a piercing whistle, when the throttle is closed. I was able to make a log file, starting it from nearly cold, getting it to closed loop mode was possible while idling because of the high idle. Then drove it, but tried driving it without giving it any gas really. Then turned around and drove it a bit with around 15% throttle. The driving starts around 6m mark on the log.

I hope the file upload worked properly. The bin is a custom one, based on BNKM, and I am using a definition file for $31.

How can I get the idle down to where it should be?
Is it normal for the knock retard to stay so consistently around 6 deg?


Other items, I checked manifold vacuum and it's in the green around 21 in Mg on my gage with this high idle. When I put it in gear, the idle drops, and then it shows in the red zone, indicating late ignition timing, only around 15 in Hg Vac

[tony-baroni]

One more update. I went out again and made a 2nd log, with more throttle, and got onto the freeway briefly. it runs like crap. Tons of knock.

I noticed a few things when I looked at the parameter list, instead of the dashboard.
Knock counts are off the charts, getting up to 50k and reseting every few seconds.

When I come to a stop, the spark advance shows 23 thousand and change, that doesn't seem right.

The check engine light came on at a stop light while the vehicle was stopped. I haven't yet figured out how to see which code was generated yet.

I'm all ears to feedback and what to try next!

Thanks all!

[tony-baroni]

Found the error codes.
35 - IAC Failure
54 - Fuel Pump Relay Failure

[sturgillbd]

Just replayed your log file. Your bin file appears to be $E6 instead of $0D. That is why you are seeing the constant knock retard. As for your high Idle, you either have the throttle stop screw open too far or you have a vacuum leak. You are getting an IAC failure because the IAC is closing completely and the pcm cannot control the idle. There are some odd things going on with the spark advance. The beginning of the log looks normal. As the log progresses, I see the timing drop from ~20 degrees down to ~5 degrees with it still idling in park. At another point, I see the spark advance pegged at 50 degrees. The PCM uses timing to help control idle speed but this seems extreme. Adjust the minimum air adjustment screw to where you have approximately 10 IAC counts at hot idle in park. You will have to power the key off and wait a few seconds for the pcm to power down so the pcm can relearn the closed throttle position. You will know when the PCM is powered down if you leave the data dash up when you key off. Tuner pro will start flashing DA Not connected at the bottom of the window. It will reconnect as soon as you key on again. It would be nice if you could read the chip and post a copy of your bin. The relay failure is a signal back into the PCM from the fuel pump relay on pin B12 of the red PCM connector. Make sure you have battery voltage on this pin with the engine running. Clear your PCM codes before adjusting the minimum air screw on the throttle body if you don't have a vacuum leak.

Thanks,
Brian

[tony-baroni]

Thanks for checking it!

I have been looking for a vacuum leak, but haven't found any. All the hoses are connected from what I can tell.

I've uploaded my bin. I thought it was a $31. The vehicle is a 1995 G30, with a 5.7L and 4L80E. Engine isn't stock...

I will look into IAC...

[sturgillbd]

I knew it wasnt $0D . Thats one reason I asked. Ill look through and see if I can find anything in the datalog that stands out. To log knock retard on some of the masks, you have to make a bin change so it shows up in the datastream. I'll see what it takes on yours in a bit.

[tony-baroni]

Thanks Brian!

I'm not sure where to go next.
Here's what I did:
1. cleared codes
2. Started engine, pulled vacuum lines one by one of the TBI to see what effect it would have. Some of them changed the idle slightly, and then I put my finger over the port on the TBI, and it would act just like as if the hose was in place. Other hoses, did not change the throttle when I unplugged them, and left them open.
The big difference came when I unplugged the vacuum hose that comes from the rear of the TBI, and plugs into a sensor (MAP?) beside the TBI. When I unplug that, the idle drops considerably, from the sound of it, near a normal level.
3. I didn't understand your IAC advice. The screw I think you're talking about is the one that sets the position of the throttle blades when the throttle is closed, right? On my engine, it is already backed out all the way. I backed it out about a 1/4 turn before the screw pulls away off the throttle bracket, because the blades are already touching the sides of the bores in the TBI.

How do I set the IAC now?

I wonder if there might be a break in my base gasket under the TBI....I've traced all the vacuum lines I can find twice now, and they all appear plugged in where they should be.

[sturgillbd]

Check your base gasket on the throttle body. If no vacuum leaks, Adjust the minimum air screw to close the throttle blades for approximately 10 IAC counts at hot idle. Clear PCM codes. You have constant knock retard. You could possibly have a bad knock sensor or bad filter board on the memcal. Do you hear any spark knock/ping? You can simulate a knock sensor on this pcm with a 3.9k resistor. It thinks a knock sensor is there but gets no knock feedback. You have extremely low timing everywhere in the datalog and that is why it is lacking in power. I also see the timing all over the place with a constant throttle/load. Something is making the PCM pull timing. As always, make sure all of the engine and PCM grounds are in good shape. Make sure plug wires aren't inducing noise back into the PCM through the engine harness. Get your fault codes cleared up and not returning then datalog again posting results here.