Achieving a stable and strong idle with cams
the thing with adding fual in a closed loop portion of the map is that it just gets dialed out. turning the biss just messes with the rest of the map... so adding timing should be done first. then if you can permanently (flash) a fuel correction then that should be explored... only as the final resort should you play with the screw.
Its all about the fuel trims and cold start.. If you can get the fuel trims in check, you'll have good cold start and a fairly good idle.. to get airflow up, you need to increase the engine speed, I'd start by doing it through the ECU if possible, then the BISS afterwards if you need to set a base..
Remember, the BISS is an air bleed, and the Idle Speed Control Valve is also an air bleed, their contributions are cumulative and therefore you need to set your BISS correctly and let the rest of the idle speed be controlled with the ICSV.. typically you set the BISS to idle at around 850-800rpm, and let the rest be handled, you only alter that if you cannot control it with the ECU.
As opposed to some other recommendations, you should be conservative about adding timing at idle, it alters your EGR temps, and alters the emissions of the car too.. These can affect how long it takes for the car light off the catalytic converter.. Also, too much timing at idle can trigger a P0300 code, especially if the car idles rough..
With that said.. There way to keep a stable idle on a MAF equipped car is to
1) Keep airflow up through the MAF, raise idle speed and add a bit of timing to increase exhaust volume which will keep the turbo spinning a little faster, hence reducing it as an intake restriction.
2) Make sure your DV/BOV is closed completely at idle, and not partially venting, that will keep the MAF from getting a disrupted airflow that can cause stalling and poor idle
3) Keep the fuel trims as close to zero as possible at idle, your not tuning the map, but tuning the trims in closed loop.. The ECU will use coolant temp to further enrich the car if the coolant or air temps are really cold, therefor just get the trims good and the car will cold start good under most circumstances
4) If you have an open filter MAF, make sure the wash from the radiator fan isn't blowing across the front of the MAF, it can disrupt the airflow slightly and raise the air temps slightly further confusing the sensor. If possible make a small heat shield to put over the side and top of the filter (if you have an open filter)
5) again if you have an aftermarket intake pipe and filter, make sure its corectly anchored, vibrations at idle could be enough to cause the car to stumble and hiccup as it bounces around, even more dramatic if it can hit anything.. Trust me I've seen this a few times..
If you have an ECU+ or another type of piggyback, explore if you can lock your idle frequency at a particular level.. By doing that, the ECU will always see a constant frequency at your idle speed, makes a big difference in idle quality with cams.. If your piggyback cannot do that, then look at your idle speed, see what frequency it is, and at rpm's below it, raise the MAF reading at RPM below it so it appears to raise the signal value.. If it idles at 44hz at 1000rpm, but its less than 30hz at 750rpm, add a few percent to the value so its closer to 44hz.. It should allow the idle to "save itself" Though I would only do this if you have no other alternatives for adjustment.
The best way to do this right is through a reflash, just as the best way to compensate for larger injectors and whatnot is through the reflash..
The closer you get everything, the less issues you'll have with idle, cold start, tip-in throttle inputs, etc.. All the annoyances that typically ruin the pleasant drivability..
Remember, the BISS is an air bleed, and the Idle Speed Control Valve is also an air bleed, their contributions are cumulative and therefore you need to set your BISS correctly and let the rest of the idle speed be controlled with the ICSV.. typically you set the BISS to idle at around 850-800rpm, and let the rest be handled, you only alter that if you cannot control it with the ECU.
As opposed to some other recommendations, you should be conservative about adding timing at idle, it alters your EGR temps, and alters the emissions of the car too.. These can affect how long it takes for the car light off the catalytic converter.. Also, too much timing at idle can trigger a P0300 code, especially if the car idles rough..
With that said.. There way to keep a stable idle on a MAF equipped car is to
1) Keep airflow up through the MAF, raise idle speed and add a bit of timing to increase exhaust volume which will keep the turbo spinning a little faster, hence reducing it as an intake restriction.
2) Make sure your DV/BOV is closed completely at idle, and not partially venting, that will keep the MAF from getting a disrupted airflow that can cause stalling and poor idle
3) Keep the fuel trims as close to zero as possible at idle, your not tuning the map, but tuning the trims in closed loop.. The ECU will use coolant temp to further enrich the car if the coolant or air temps are really cold, therefor just get the trims good and the car will cold start good under most circumstances
4) If you have an open filter MAF, make sure the wash from the radiator fan isn't blowing across the front of the MAF, it can disrupt the airflow slightly and raise the air temps slightly further confusing the sensor. If possible make a small heat shield to put over the side and top of the filter (if you have an open filter)
5) again if you have an aftermarket intake pipe and filter, make sure its corectly anchored, vibrations at idle could be enough to cause the car to stumble and hiccup as it bounces around, even more dramatic if it can hit anything.. Trust me I've seen this a few times..
If you have an ECU+ or another type of piggyback, explore if you can lock your idle frequency at a particular level.. By doing that, the ECU will always see a constant frequency at your idle speed, makes a big difference in idle quality with cams.. If your piggyback cannot do that, then look at your idle speed, see what frequency it is, and at rpm's below it, raise the MAF reading at RPM below it so it appears to raise the signal value.. If it idles at 44hz at 1000rpm, but its less than 30hz at 750rpm, add a few percent to the value so its closer to 44hz.. It should allow the idle to "save itself" Though I would only do this if you have no other alternatives for adjustment.
The best way to do this right is through a reflash, just as the best way to compensate for larger injectors and whatnot is through the reflash..
The closer you get everything, the less issues you'll have with idle, cold start, tip-in throttle inputs, etc.. All the annoyances that typically ruin the pleasant drivability..
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