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| dan0617 | Anyone ever run without IAC? | ||
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Senior Guru
 
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Just wondering if there would be any benefit to part throttle tuning (possible elimination of some cam surge) if I were to put the car into diagnostic mode (effectively closing the IAC), then umnplug the iac and turn the throttle adjustment screw ahead until desired idle is reached. Anyone ever done this? Also, is there any benefit in setting the TPS any higher than .54 volts?
If nobody has tried it then I'll try it tomorrow and let you all know what happened. |
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Posted on: 2009/4/25 2:33
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´89 Vert, 383, 230/236 cam, AFR 195's, LT Headers, HSR intake, 2800 stall, Zex 200 shot, ET Street Radials, tune by me. Runs were with D36 3.07's. On spray, 10.55 @ 132.78, 1.55 60 ft. On motor, 12.08 @ 113.15, 1.66 60 ft. |
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| CentralCoaster | Re: Anyone ever run without IAC? | ||
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People do this all the time, but I question it.
The idle speed is set in the computer right? So if you open the throttle screw far enough, the computer will compensate but closing the IAC all the way, at which point it has no more control. So I guess you can hold your idle high, but I would expect it to be somewhat erratic depending on your setup, the IAC wouldn't help any. It seems like the better way to go would be reprogramming the idle speed first. Obviously a big cam can't idle at 600 rpm easily. |
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Posted on: 2009/4/25 3:55
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1985 Z51, ZF6 |
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| CFI-EFI | Re: Anyone ever run without IAC? | ||
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I don't know how big your cam is, but I do know that adding timing advance at idle speed can strengthen and smooth an unruly idle. Disconnecting the IAC eliminates any increased cold idle speed. I agree that the solution is more in the software than the hardware. I have seen where once the proper idle speed has been established, that the minimum air adjustment was set higher to prevent over compensation by the ECM/IAC from killing the engine.
My experience with altering the TPS voltage was that too much made the throttle ultra sensitive. It was hard to hold a steady speed while cruising on the highway. It made the car uncomfortable and of course, it didn't make any more power. RACE ON!!! |
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Posted on: 2009/4/25 16:07
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| bogus | Re: Anyone ever run without IAC? | ||
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Grand Imperial Pooh-Bah
 
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It would also eliminate any idle adjustment for load - if you have AC, that could get icky.
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Posted on: 2009/4/25 17:20
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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| dan0617 | Re: Anyone ever run without IAC? | ||
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Quote:
Well, all of the above posts are correct. I tried this today. What CFI quoted above got me thinking though, so I tried something else...... My problem wasn't erratic idle, it was an ultra lean condition on very light tip-in after driving at very light throttle for a distance. I cranked up the idle screw after resetting the IAC and unplugging it. The car idled and ran fine (as CC suggested it was a hair more erratic idling than with IAC but not bad), have no tip-in problem, but still have the same light cam surge so no help there. But, I got to thinking about the TPS voltage. When the problem was occurring it was acting as if it isn't sensitive enough to my light tip in. I had it set at .53 volts. I messed around for quite a while till I got the iac at around 15 steps at idle and have the TPS set at .67 volts at idle. (That is harder to do than it sounds!) Haven't gotten to drive very far yet but the light throttle tip in problem seems to be gone and the cam surge is less than it has been so far. The .67 volts is a little sensitive but not too unruly. After I drive more and assure the problem is gone maybe I'll bump it down to .63 and try that. Andy, you are also correct. I do have A/C and when I turn it on the idle drops to about 700 and the cam doesn't like to idle that low. I'm glad I messed around with it but I am going to try to retain the IAC function. I think it is just a fine line adjustment when the cam is fairly big, trying to get the IAC steps, the throttle screw, and the TPS voltage in a range that will work for idle, and light throttle (light enough that the idle control circuit is in use). |
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Posted on: 2009/4/25 21:20
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´89 Vert, 383, 230/236 cam, AFR 195's, LT Headers, HSR intake, 2800 stall, Zex 200 shot, ET Street Radials, tune by me. Runs were with D36 3.07's. On spray, 10.55 @ 132.78, 1.55 60 ft. On motor, 12.08 @ 113.15, 1.66 60 ft. |
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| dan0617 | Re: Anyone ever run without IAC? | ||
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Senior Guru
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Well, got to drive some more and the problem is still there. When I drive at about 68 or 70, light throttle holding steady speed, then give it a hair more gas to slightly accelerate, it goes completely lean, like it ran out of gas. Goes right to 22.4 on the AFR gauge. If I give it more gas it clears up. As stated above, when I close and unplug the IAC and turn the idle screw up to maintain a 900 rpm idle, the problem does not exist. Cam surge is a little worse though, and turning the A/C on drops the idle to about 700 and makes it surge. I hate to run without IAC but for now I will.
What causes the IAC to open and close? It can't be by the computer sensing rich or lean or my problem wouldn't exist. If it weren't opening under extremely light acceleration all would be fine. I tried to close up the throttle plates to the point the IAC was almost all the way open but the idle gets surgey and low. If I open it just to the point that the idle is ok, the problem still exists. It will only get to about 19.5 or 20 on the AFR gauge instead of pegging at 22.4 but it is still no good. |
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Posted on: 2009/4/27 1:56
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´89 Vert, 383, 230/236 cam, AFR 195's, LT Headers, HSR intake, 2800 stall, Zex 200 shot, ET Street Radials, tune by me. Runs were with D36 3.07's. On spray, 10.55 @ 132.78, 1.55 60 ft. On motor, 12.08 @ 113.15, 1.66 60 ft. |
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| anesthes | Re: Anyone ever run without IAC? | ||
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Master Guru
 
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Need more AE. HSR right? Quote:
Probably entering PE at that point. Quote:
There is all sorts of routines like the throttle follower that changes IAC. I zero a lot of them out, because it does some funny things. I still think your lean problem is AE related. Quote:
I thought you were doing your own chips? Or am I mistaking you for another dan? -- Joe |
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Posted on: 2009/4/27 2:45
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| dan0617 | Re: Anyone ever run without IAC? | ||
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Senior Guru
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Thanks for the advice. No, I don't do my own chips, I just don't have the time for the learning curve and the testing and retuning and such. Wish I did. I have had Azzato and Pcmforless do chips for me. For both setups the Azzato chips have been much better. Have had to make some tweaks and am glad I have an AFR gauge but Azzato has done the best so far. I'm trying to decide if I should have him try more AE to clear up the problem or to just run without IAC. I do still have the high idle at warm-up even without IAC, which I didn't think I'd have. The only time I see the IAC helping at this point is to smooth out the idle a little more, and when I turn the A/C on, which isn't often since it is a vert. When I give it a little more gas and it clears up, it is not entering PE mode. Don't have to give it that much more gas for the clear up to happen. That makes me unsure of it needing more AE. You could be right tho. I really thought it was a specific block learn cell too lean but the block learn that it is in when the problem occurs is also used other times, which makes it whacky. It obviously gives it as much fuel as possible during the lean condition, which still isn't enough, then the next time that block learn cell is used it is way too rich and needs to correct back the other way. Again, can all be seen on the AFR gauge and with Tunerpro datalogs. One other thing I think I'm gonna try is to have the target AFR set at 15.5 instead of 14.7 at all part throttle driving. Seems that there is no cam surge when the AFR is in the 15.5 range. Anyone else doing this? Should I also try 15.5 target at idle since I am very near idle conditions when I'm at very light throttle highway cruising? |
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Posted on: 2009/4/27 14:10
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´89 Vert, 383, 230/236 cam, AFR 195's, LT Headers, HSR intake, 2800 stall, Zex 200 shot, ET Street Radials, tune by me. Runs were with D36 3.07's. On spray, 10.55 @ 132.78, 1.55 60 ft. On motor, 12.08 @ 113.15, 1.66 60 ft. |
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| anesthes | Re: Anyone ever run without IAC? | ||
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Master Guru
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Jesse is a pretty good tuner, and he has a lot of track experience on his own car. Anyhow, some of the spark correction tables alter idle too, if the BIN decides IAC changes are doing nothing. There is just a lot of control and simply unplugging the IAC won't get your steady stable idle you want with correction off. Again, I zero out a lot of those tables because with big cams it becomes a battle between the ECM trying to fix a lopey cam, and making it WAY WORSE. Nothing wrong with changing your target AFR, and you can almost pull it off in closed loop by changing your 02 thresholds. Or you can just run open loop, and dial your fuel map in with the wideband. A lot of this will be nearly impossible though unless Jesse has your car for a few days, or you start your own tuning. EFI is fun stuff, but there is a lot of 'fluff' that I disable to make life easier. In the end, I end up with fuel maps that almost mimic a carb, and advance curves that mimic vac advance distributors. With a stock car, I wouldn't do such a thing. But dude, your in the 11s.  -- Joe |
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Posted on: 2009/4/27 14:35
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| CFI-EFI | Re: Anyone ever run without IAC? | ||
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Senior Guru
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The IAC opens and closes as commanded by the ECM in order to attempt to maintain the idle speed. I highly doubt the IAC is causing your lean mixture. Especially not at 68 to 70 mph. Certainly Joe knows computers and programming much better than I do, but one problem I am aware of with cams with a lot of overlap that won't idle, is in the minimum air adjustment. With the idle programmed at a workable speed there is usually still a lope. The spec minimum air adjustment has the throttle blades closed so far that the idle speed is allowed to drop too low. As the engine lopes, and the engine drops below the programmed speed, the ECM/IAC open to raise the speed. The open IAC allows the speed to exceed programmed and the IAC closes. The ECM/IAC can't react fast enough. As the target idle speed is exceeded, the IAC gets closed again. The idle goes from too fast to too slow in a widening range. The idle speed is in a death spiral as the highest speeds and lowest speeds get further and further apart and the engine finally dies. Have your idle speed programmed into your chip where it will maintain a reasonable idle (don't forget the timing advance) and then set the throttle stop screw (minimum air adjustment) 100 - 200 rpm below the idle speed. The higher minimum air adjustment will prevent the idle speed from swinging in such a large spiral. Hopefully that will eliminate the dying at idle. RACE ON!!! |
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Posted on: 2009/4/27 14:54
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| dan0617 | Re: Anyone ever run without IAC? | ||
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Senior Guru
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Actually that is how I originally sat up the IAC. I had it at about 40 steps, and the tps at .53, then took the tps up to about .65. The timing at idle is 27 degrees. The idle is set at 875 in the chip and the idle is actually perfect this way. The only problem is some cam surge, which I can live with, and the lean problem when I tip the throttle in very lightly from a very light cruise. It is definitely IAC related because when I force the IAC close and disconnect it and crank the throttle screw ahead I can drive it all I want and the problem doesn't exist. I dropped the IAC down to 5 steps at idle and the problem gets worse. I've tried opening it up to like 130 steps at idle and the problem almost completely goes away but the idle gets very jumpy then and there is no compensation when the A/C is on so I'm better off to run without IAC then to have it this far open. I actually have done alot of researching today now that Joe pointed me in this direction, and I'm now thinking that maybe setting it up so the IAC follower doesn't start "following" the throttle till a higher percentage of throttle position just might correct the problem. I'd try having Jesse turn the throttle follower off completely by zeroing it out but I'm afraid when I jump off the throttle from WOT it would stall out. It isn't stalling out with the IAC disconnected so maybe it wouldn't. Anyway, I think it is worth a try. Thanks for all the suggestions so far, I'll keep everyone updated. |
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Posted on: 2009/4/27 18:52
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´89 Vert, 383, 230/236 cam, AFR 195's, LT Headers, HSR intake, 2800 stall, Zex 200 shot, ET Street Radials, tune by me. Runs were with D36 3.07's. On spray, 10.55 @ 132.78, 1.55 60 ft. On motor, 12.08 @ 113.15, 1.66 60 ft. |
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