Idle tuning problem

I've noticed that my idle is inconsistant. I don't believe it has anything to do with the speed senor because I've changed that expensive sensor a few times, yet the problem persists with idle speeds being as much as 2500 rpms with the throttle closed. It seems to be connected to full throttle events more than anything else. When the idle speed is high it will at times correct itself after an extended idle period. The air idle port in the throttle body is clean and the throttle blade is adjusted just barely open. Can the automatic idle speed motors get sticky over time?
I suspect it's in the tune because in the past I have times when the idle acted normally all the time. Which tables in MPTune affect the idle and is there a process for adjusting this.
Is there a way to bench test the automatic idle speed motor?

If everything is clean, it could be a bad AIS that doesn't throw a code. I think you can test it with the diagnostic functions in MPSciLink, but I'm not positive about that. What size TB do you have on the car? I've found the 58mm TBs need a lot of help in the idle department for my cars. I generally look at the values in the stock cal and the S60 cal for TB type tables and adjust according to the TB size.

I may have found the problem, still working to verify it. I was looking at the wiring diagram for my "85" AIS and noticed that some colors don't match and it looks like the TPS only had two wires. I cant remember if I added extra wires to the 87 LM I'm running, its been years since I did that. I have an 89 throttle body and a four wire AIS weather pack plug. I don't even remember what the original AIS plug for the pull through TB looked like, I think it would only have two wires. I will respond back if I find I'm missing a wire. That would certainly explain things. If the wires are there, its back to square one.
I do have a 58 mm TB. I have a stock cal that I could look at for settings but not the S60 settings. I also wouldn't know under what heading and sub heading in the turbonator cal to look for the setting. Can you help?

I apparently got a 88-89 TPS/AIS harness with plug which plugged into my existing "85" harness. 1987 L/M red plug pins #16, #18, #20, #22 all have wires at the position and all wires at the original harness plug have been spliced and shrink wrapped indicating re-wiring. Considering that after the engine started and ran, the fact that it returns to low idle means both sets of winding have complete circuits and the AIS is operating. It appears I am back to calibration adjustments.

What base cal are you using? The turbonator stuff does include the S60 for the SMEC cals. You can load that as a comparison cal and then look at the AIS tables to see what the differences are. One word of caution is to make sure they're both scaled for the same MAP and fuel injectors, or otherwise it will be off. I save as for the S60 cal to indicate which scaling changes that cal is setup for.

As far as which tables, go to the Idle section and compare all of the AIS tables. I just read through my log, and I really have a lot of tuning to do with the new parts once I get a clutch which will allow me to drag the brakes and set the Peftbl.

I have a smec tune from Brian which should have those tables. I dont know if there will be similar tables in my lm tune. I am making a big change on any table I always copy down the original settings so I can get back to where I started.
Thanks Cordes
Jeff

I recently dynoed the car and ultimately discovered that my 3 bar was bad. The fuel settings from the dyno turned out to be lean. So I will go back again to rest them to increase fuel.

Cordes, well I gave this process a try and the result was the engine idled at 2500 all the time and I couldn't get it to go down so I started over by returning all AIS settings to my original ones which resolved the problem. I found that the following files in AIS control had significant differences. Brake Override From Delta, Forward AIS Steps No Slope, Idle Drive Speed From Temp, Reverse AIS steps No Slope and Idle Speed Park Neutral From Temp. This last one I think may have something to do with high idle because the slope has its last point at 195 degrees 923 rpm where as the stock SMEC tune is set at 169 degrees 923 rpm. I'm guessing the LM calibration runs higher rpm to reduce engine temp.
It was a good learning experience and I'm glad I tried it. I reproduced the data here to help other LM tuners.
Jeff

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Originally Posted by jeff1234

Cordes, well I gave this process a try and the result was the engine idled at 2500 all the time and I couldn't get it to go down so I started over by returning all AIS settings to my original ones which resolved the problem. I found that the following files in AIS control had significant differences. Brake Override From Delta, Forward AIS Steps No Slope, Idle Drive Speed From Temp, Reverse AIS steps No Slope and Idle Speed Park Neutral From Temp. This last one I think may have something to do with high idle because the slope has its last point at 195 degrees 923 rpm where as the stock SMEC tune is set at 169 degrees 923 rpm. I'm guessing the LM calibration runs higher rpm to reduce engine temp.
It was a good learning experience and I'm glad I tried it. I reproduced the data here to help other LM tuners.
Jeff

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Thanks for sharing that info. I'll certainly be looking back to that post if I have LM high idle issues.

Hello all, the problem still exists. The symptoms I'm seeing now are similar to my original post. I do have a 58 mm throttle body but the car idles frequently at 1000 rpm, so it does work at times.

A better description of what is happening... seems like it is more prevalent after doing some full throttle runs during tuning. I settles to about 1500 rpm, then abruptly drops just slightly below 900 and then stabilizes. soon it starts to idle higher again. Strangely, it can also idle correctly during the same conditions. I'm wondering what table tells the the ECM to drop to idle. The AIS rate is set at 7, the AIS temp swap is at 127 and out. Position AIS motor idle is at 26 and out. Idle speed drive from temp, point one is 30 degrees at 923 rpm, second point is at 168, 771 rpm.
Do these numbers match your LM tunes?
Is it possible one of these is causing the idle problem?
Jeff

Jeff,
the LM also raises RPM if the electrical load is high like when Rad fan is on or when Alt is have issue. New brushes fixed mine a few a few weeks ago

Here's what I do on all my tuneable manual blowthrough TD's. you take the AIS out, Break off the spindle head, fill the passage way with gorilla glue and let cure for a couple days. Put AIS motor back on throttle body and put it back on the car. Now there's a table that adds timing when the car is a certain temp. Anything under 100 degrees of engine temp add 2 degrees of timing. Set base idle at 900rpms. Car will now start and idle at 1100 rpms from -10 degrees F to under 100 degrees. Once over 100 degrees of engine temp idle will be 900rpms. Rev's drop right to idle so you'll have to increase your shifting speed and adjust your throttle applications a tad. But the shifts won't be as jerky. So much better to drive then trying to have the ECU help you. Add a unsprung clutch disc and it'll get better.

Miles, my alternator is only a couple of years old, it was a rebuilt from AZ so it might be a problem. I get about 14.6 volts during charging. Should it be more? I'm going to see if the high idle is corresponding with the cooling fan running. It makes logical sense, higher load from the fan plus the added load of the alternator in charging mode. I suppose that once the fan kicked out the idle wouldn't drop sharply but would drift down slowly.

I understand that you are defeating the passageway that allows additional air to get past the throttlebody to the intake. Can you tell me the name of the table?
Thanks.

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Originally Posted by jeff1234

I get about 14.6 volts during charging. Should it be more? I suppose that once the fan kicked out the idle wouldn't drop sharply but would drift down slowly.

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From my believe 14.6V is a bit high but My LM is charging in the low 14s at the battery. But inside the cabin the voltage is 13.6-13.8V.
To check my Alternator, I turn everything on at idle including the rad fan.
I did find when the brushes were "bad" the voltage dropped to 10V when the Rad Fan turned on. The AIS quickly increased to 2000-2500 RPM but dropped slowly when the load was reduced.

I will give that a try, its an interesting test .

Quote:

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Originally Posted by jeff1234

I understand that you are defeating the passageway that allows additional air to get past the throttlebody to the intake. Can you tell me the name of the table?
Thanks.

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It's been 10+ years since I've messed with it and don't have my laptop or my td's with me at the moment. once it's found it's pretty obvious