Idle dipping below commanded

[calvinespree]

I've been working on tuning this car quite awhile now here and there when I have time (Working 7 days a week sometimes 16 hours a day and having a newborn here) it's just about nailed down but I notice if I ease into the throttle real lightly my idle dips down to around 500 and comes back up when I'm commanding 850. I played with the throttle follower tables a little bit and I didn't really notice a change, I was just looking to get a second opinion as to what it could be rather than just changing things in the tune without knowing the possibilities. It's the same thing if I rev it in park itll come down below idle and bounce back up. In one case it died on me trying to come down from a rev.
Could this be spark transitioning from the high octane back to idle? Or an airflow situation.
It's a 2010 ss long tubes, cold air intake, 27x/29x cam .625 lift, pulley, tb spacer.

[mowton]

Can't open tune or log file.....:-)

try adding .25 g/sec to min air table from 1200 rpm and down. See if better or worse. repeat as needed. Add 2 degrees of timing to the 400 rpm. these are just guesses until we can see the logs and tunes.

Ed M

[calvinespree]

Can't open tune or log file.....:-)

try adding .25 g/sec to min air table from 1200 rpm and down. See if better or worse. repeat as needed. Add 2 degrees of timing to the 400 rpm. these are just guesses until we can see the logs and tunes.

Ed M

I will post one soon as I get to my laptop been in the shop all day thank you

[calvinespree]

Can't open tune or log file.....:-)

try adding .25 g/sec to min air table from 1200 rpm and down. See if better or worse. repeat as needed. Add 2 degrees of timing to the 400 rpm. these are just guesses until we can see the logs and tunes.

Ed M

Heres a short log and my tune, thank you

[calvinespree]

Also seems to miss from a cold start. Most likely fuel related, my wideband died on me so I'm waiting on the new sensor to come in

[calvinespree]

Anyone can point me in the right direction so I know where to start without messing anything up or getting worse

[GHuggins]

Have you tried what Ed told you? Otherwise I would wait on the A/F sensor so you can see what your fueling is at the time of problem...

[calvinespree]

Have you tried what Ed told you? Otherwise I would wait on the A/F sensor so you can see what your fueling is at the time of problem...

I added to the base airflow with no change in the problem I was having. I kept adding until it was at the point of the rpms hanging and it made no difference

[mowton]

After looking at your log (believe it was taken before you increased Min Air per my direction), you have too much min air and / or MAF to start. That is eveident by the advance spark graph. See the way it is toggling between -5 degrees and 20 degrees, that tells me the timing is biased way down to try and keep the idle rpm at the commanded rpm. Essentially it is fighting the air to keep it right...does that make sense?

I would go back to your tune that created the log, pull 15% out of the MAF and min air in the idle areas as a test. Also put the enable RPM error for the Proportional and Integral idle back to stock.

Ed M

[C5 2000]

Compare with stock file return Fast Torque Exit Delta to stock, Idle Adaptive Spark Control Overspeed & Underspeed back to stock. Then you might want to change High RPM Re-enable to 400

[calvinespree]

After looking at your log (believe it was taken before you increased Min Air per my direction), you have too much min air and / or MAF to start. That is eveident by the advance spark graph. See the way it is toggling between -5 degrees and 20 degrees, that tells me the timing is biased way down to try and keep the idle rpm at the commanded rpm. Essentially it is fighting the air to keep it right...does that make sense?

I would go back to your tune that created the log, pull 15% out of the MAF and min air in the idle areas as a test. Also put the enable RPM error for the Proportional and Integral idle back to stock.

Ed M

Did that just now didnt notice a change. Heres a log of the idle dipping down when i ease into the throttle and when i rev it. By listening to it, it almost seems that theres a transition from the idle tables and thats what makes it do it, it has a different sound for a few seconds and then the idle takes over and the lope comes back.
Also my current tune is attached

[calvinespree]

Thank you i tried that and noticed no difference as well

[mowton]

Did that just now didnt notice a change. Heres a log of the idle dipping down when i ease into the throttle and when i rev it. By listening to it, it almost seems that theres a transition from the idle tables and thats what makes it do it, it has a different sound for a few seconds and then the idle takes over and the lope comes back.
Also my current tune is attached

Take another 10% off your MAF and expand beyond idle range a bit more with the 15% first. It seems the fueling at idle is beginning to toggle a bit. Also, add 3 degrees to the entire idle spark tables.

Thanks

Ed M

[GHuggins]

OK, so you've got a going into idle drop below idle stumble... Not sure I worded that correctly, but I'm going to tell you to do pretty much the oposite of what most will, because I have found this to work the best, BUT it only works if your injection timing, VE and fueling have been dialed in correctly, which is what I'm really wondering with the cam you've got has been or not. I don't have my laptop to view your tunes or datalogs. Just going off of what your describing...

With your min airflow tables dialed in pretty close to where they should be - in other words with your idle advance not bouncing all over while it's idling in your datalog, lower your idle advance timing about 7 to 10 degrees from where it was before you started playing with everything - overall available timing advance will be somewhere in the neighborhood of 10 degrees max. Make sure you still have about 5 to 10 degrees left in your table for "torque addition". After this go to your main timing table and increase your idle timing areas about 5 or a little more to "optimize" your idle timing. You'll notice the optimal area just by smoothness and sound of the idle Then finally go to your underspeed and overspeed timing tables and "increase" these by 1.5 or so percent (first timing number somewhere around 2.4 degrees). Doing this will make your motor very "torqy" in the idle areas. Basically you'll be power tuning your idle. I've found on manual transmission vehicles you can almost pop the clutch without giving any fuel and the motor will pick back up from a 200 to 300 rpm level without issues. Like I said though, most will tell you to do the oposite to keep a lot more "torque reserve" on hand. Simply put this is exactly how I fixed a bad idle surge on our twin turbo vette and it's still idling great and smooth.

If this doesn't have any effect, start looking at your injection timing. Basically you'll need to raise your boundary "retard the timing of the injectors" untill you have made your fueling as rich as possible, then unfortunately start all over with everything.

Hope all this actually helps you.

[calvinespree]

Take another 10% off your MAF and expand beyond idle range a bit more with the 15% first. It seems the fueling at idle is beginning to toggle a bit. Also, add 3 degrees to the entire idle spark tables.

Thanks

Ed M

I'm doing this right now so I can check it out on my way to work. thank you for the help I will let you know the results

[calvinespree]

OK, so you've got a going into idle drop below idle stumble... Not sure I worded that correctly, but I'm going to tell you to do pretty much the oposite of what most will, because I have found this to work the best, BUT it only works if your injection timing, VE and fueling have been dialed in correctly, which is what I'm really wondering with the cam you've got has been or not. I don't have my laptop to view your tunes or datalogs. Just going off of what your describing...

With your min airflow tables dialed in pretty close to where they should be - in other words with your idle advance not bouncing all over while it's idling in your datalog, lower your idle advance timing about 7 to 10 degrees from where it was before you started playing with everything - overall available timing advance will be somewhere in the neighborhood of 10 degrees max. Make sure you still have about 5 to 10 degrees left in your table for "torque addition". After this go to your main timing table and increase your idle timing areas about 5 or a little more to "optimize" your idle timing. You'll notice the optimal area just by smoothness and sound of the idle Then finally go to your underspeed and overspeed timing tables and "increase" these by 1.5 or so percent (first timing number somewhere around 2.4 degrees). Doing this will make your motor very "torqy" in the idle areas. Basically you'll be power tuning your idle. I've found on manual transmission vehicles you can almost pop the clutch without giving any fuel and the motor will pick back up from a 200 to 300 rpm level without issues. Like I said though, most will tell you to do the oposite to keep a lot more "torque reserve" on hand. Simply put this is exactly how I fixed a bad idle surge on our twin turbo vette and it's still idling great and smooth.

If this doesn't have any effect, start looking at your injection timing. Basically you'll need to raise your boundary "retard the timing of the injectors" untill you have made your fueling as rich as possible, then unfortunately start all over with everything.

Hope all this actually helps you.

I haven't changed anything with my injection timing and I'm running pure MAF at the moment would this still possibly work?

[GHuggins]

That's a pretty impressive cam to not dial in the injection timing, but there are ways to tune without dialing it in... You just don't benefit as much, especially in the mpg department. As for the pure MAF, shouldn't hurt anything. Not bucking any at light cruise? So I don't guess your going the idle power tuning route. That's fine, just let us know how it goes.

There's also a couple of other airflow tables that address idle surging and dipping (proportional and integral), but without being able to really stay at it or a tuning book to guide you, they're a real pain to dial in. Basically you add a little to the proportional then take away a little (somewhere around what was added to the proportional table) from the integral. Big cams will play with these a little, but usually if the min airflow table is close, then these should be too.

[calvinespree]

That's a pretty impressive cam to not dial in the injection timing, but there are ways to tune without dialing it in... You just don't benefit as much, especially in the mpg department. As for the pure MAF, shouldn't hurt anything. Not bucking any at light cruise? So I don't guess your going the idle power tuning route. That's fine, just let us know how it goes.

There's also a couple of other airflow tables that address idle surging and dipping (proportional and integral), but without being able to really stay at it or a tuning book to guide you, they're a real pain to dial in. Basically you add a little to the proportional then take away a little (somewhere around what was added to the proportional table) from the integral. Big cams will play with these a little, but usually if the min airflow table is close, then these should be too.

I'm gonna try to go at it today I just got off from my night job and I have a few cars in the shop to finish up then all time is directed to fixing this. The car runs perfect any other time, pulls hard no bucking or surging. I pulled 10% more maf and base airflow still no change. Added 3 degrees of timing as well. It seems like it's a certain point in the throttle when I tip in real slow that closes it a little causing this (if that's possible)

[GHuggins]

I'm gonna try to go at it today I just got off from my night job and I have a few cars in the shop to finish up then all time is directed to fixing this. The car runs perfect any other time, pulls hard no bucking or surging. I pulled 10% more maf and base airflow still no change. Added 3 degrees of timing as well. It seems like it's a certain point in the throttle when I tip in real slow that closes it a little causing this (if that's possible)

If all else is running correct, try the idle dial in first. BUT you typically will have to redo these sections of the VE table, because you'll find less fuel being required to maintain idle speed, so if you wanted once your dip is fixed, you could adjust the injection timing to optimize everything. That's if it even needs adjusting. In other words, if you haven't adjusted it at all yet.

[calvinespree]

If all else is running correct, try the idle dial in first. BUT you typically will have to redo these sections of the VE table, because you'll find less fuel being required to maintain idle speed, so if you wanted once your dip is fixed, you could adjust the injection timing to optimize everything. That's if it even needs adjusting. In other words, if you haven't adjusted it at all yet.

Yeah I haven't touched injection timing Or the ve tables. It doesn't dip coming down from a rev anymore like it was but now I have low rpm bucking which i didn't have before lol. Guess we can't have it all huh
It still does the same thing if I ease into the gas lightly and I mean LIGHTLY the rpms go down to 500 soon as it catches and it'll stay there until I give it more throttle