B4317 to drop idle faster when coming to a stop?
My 97 A4 corvette seems to want to push some when coming to a stop like the idle is not coming down fast enough. After I make the stop it will drop right down to the set idle speed. Is the table B4317 the one I need to change in the problem area? I have never messed with this table before so I'm not sure.
Do I get 3 guesses?My guesses are (if it's not a mechanical issue like a vacuum leak), the Desired Airflow is off and/or throttle cracker is adding too much airflow and/or maybe timing is too high.
What's done to the car?
Just a bolton car. Well also has a ported throttle body. I hear alot of people having this trouble after porting but they all say it just needs to tune tweaked a little. I mean it's not bad but I would like it better if it would drop just a little sooner. I may increase that table so it will decay more out in the speeds from 15 mph and lower. That's the only speed I can feel the problem. Oh I don't have any vacume leaks or anything.
If extra air is passing around the throttle body, then I'd say it might be something as simple as adjusting your Desired Airflow table. Basically, the port job might have gone a tad too far and you now have done the equivalent of drilling out the hole in the throttle body blade IMO. So, I'd say log the idle trims and you'll most likely find that you'll have to pull some out of the Desired Airflow table in the Idle folder.Originally Posted by mvvette97
If you do that, everything checks out, and you're still having a problem, I'd pull some airflow out of your throttle cracker table. I don't think there's a need to touch any decay tables though.
If I was to pull some out of the desired airflow wouldn't that change the airflow at all speeds? Everything seems fine other than when pulling up to a stop from about15 mph and slower just as the tranny shifts down to 1st gear. I know normally ya should not feel it down shift to 1st when coming to a stop but it does because of the higher idle. When it downshifts in all the other gears when slowing down it seems pefect. I guess I was just thinking that if it was able to pull more airflow at 15 mph down to 5 mph or so that it would not hang as long. Just as a make a complete stop it will rest at the desired idle speed of 700. I'm still trying to figure all this tuning stuff out, ha
Check the idle trims either way. If they're out of their range of adjustment, it can cause similar problems to what you're experiencing. Given it's just a bolt-ons car, I'd find it hard to believe that you really need to touch much in the way of throttle cracker, follower, etc. unless it's a matter of preference. Regardless, tuning the Desired Airflow with the idle trims is kinda like tuning fueling during closed loop with fuel trims. The car is going to try to maintain the numbers it knows to maintain (14.7:1 AFR or in this case the desired idle RPM). If something is off, it'll try to trim it back into place. But, it only has so much room to work with. By ruling out the Desired Airflow as the source of the problem, then you know to go somewhere else. Kinda like Monopoly. You gotta pass Go to collect $200...unless you're going straight to Jail....and you don't want to go to metaphorical jail. LOL
Once you have your idle trims in line.....if you're still experiencing the problem, you could try shifting B4403 up a cell or two. In other words, copy from the 2nd or 3rd cell to the bottom and then paste it in the first cell to shift the table up 1 or 2 cells. I'd try a test tune with the table shifted up 2 cells first to see how the car reacts.
ok so exactly what should I log?
Log while in D from a cold start:
IAC - Long term correction, in gear, A/C Off {GM.IAC_LTD_DMA}
IAC - Short term correction, in gear, A/C Off {GM.IAC_STD_DMA}
Idle Airflow Correction AC Off, In Gear {CALC.RAFIG} - this is a calc'd PID adding the first two together.
Log while in P from a cold start:
IAC - Long term correction, in P/N, A/C Off {GM.IAC_LTPN_DMA}
IAC - Short term correction, in P/N, A/C Off {GM.IAC_STPN_DMA}
Idle Airflow Correction AC Off, P/N {CALC.RAFPN} - this is a calc'd PID adding the first two together.
(M6 cars just have to do the in-gear, not the P/N)
I would log those with Desired IAC Airflow {GM.IACDES_B}. IIRC, IACDES_B will be what you have in your Desired Airflow table +/- any IAC adders (including the LT & ST trims above). I'd start logging about 10 seconds after you start it up to make sure the other adders aren't interfering. So, all you really need are these PIDs and coolant temp. Try to keep the total number of PIDs to a minimum to make sure the scanner is logging at a higher frames/second rate. Then, it's just a matter of logging idle behavior from a cold start until the vehicle has warmed up to operating temps for a minute or two.
To view the data, I just use the graphs on B or C in the Dashboard (F10). Pick a temp to start with in the tune (i.e. 104*F). So, I'd scroll over until I found where my ECT was 104*F in my logged data. You want to highlight the graph for the section that ECT registered 104*F. This will give you an average of the PID outputs during that time. If you're using the calc'd PIDs above, the average correction is what you need to make to the Desired Airflow table in the tune for 104*F (i.e. add the value you see to the existing number in the tune). If you're using the IACDES_B PID, the number you see is what you type in the tune straight up. JUST MAKE SURE THE UNITS OF MEASURE ARE CONSISTENT. Do this for as many data points as you can from a cold start in P and then do the same for in gear the next day. For the points you don't hit, you can kinda guess-timate where they need to be.
That's how I adjust my Desired Airflow table.
Last edited by SSpdDmon; August 5th, 2009 at 01:30 AM.
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