IAC ADJUSTMENT WITH WEATHER CHANGE?

#1
So I have ben driving my rebuilt 86 engine since May and it ha been flawless Starts right up, idles smooth as silk. I had adjusted the TPS to 42 and the IAC setting to 18. This has stuck all year. This morning (in Connecticut) it was a bit cold and when I cranked the engine it would not stay running until I fed gas. When I got to where I was going I checked idle, etc. Idle in neutral was about 625 (usually about 850) and jumping all around. TPS was at 42 but IAC was at 170. Drove it home a couple of hours later and it still needed gas to start but when I got home the IAC was down to 80. Tonight it started right up and seems to idle a lot better but not as perfect as it used to but the IAC is still around 80.

Question? Does the IAC setting usually require adjustment when the temperature drops? I am reluctant to mess with the adjustment if it's just some kind of hiccup. What do you guys think?

Thanks
 
#2
Typically, no. You don't need to adjust the IAC for weather. Once you set it, you forget it.

If I were having your issue, I'd start looking for a vacuum leak. Cold weather, maybe you have a cracked hose or something and its sucking air at idle.
 

earlbrown

runs with scissors
#3
You got something going on that's screwy. When you were happy at 18, that was pretty high. Way higher than I like mine.

When it was acting up, any chance you had your foot on the gas when you started the car?
 
#4
In response to Turbo6inKY I suspected a vacuum leak but found none. When IAC got a lot better and idle too I ruled out a vacuum leak because my thinking was that if it was a leak it would not have gotten better (unless of course our brilliant ecm's can correct for vacuum leaks on the fly)
Responding to earlbrown, my foot was definitely not on the gas. As to IAC setting, my reading is tht anything between 0-20 that gives you good results is ok. Before this issue, my idle performance was perfect so I left it alone.

I think I will wait and see what happens in the coming days. Perhaps the ecm hiccupped and will re-learn in time. We shall see.

Thank you both for your input.
 
#5
In response to Turbo6inKY I suspected a vacuum leak but found none. When IAC got a lot better and idle too I ruled out a vacuum leak because my thinking was that if it was a leak it would not have gotten better (unless of course our brilliant ecm's can correct for vacuum leaks on the fly)
Once the car warms up enough to go closed loop, it'll compensate for the vacuum leak and the idle will smooth out. You'll see your BLM numbers walk up above 140.
 

earlbrown

runs with scissors
#6
When everything is running right, the location of the IAC 'doesn't matter' as long as it's not maxed out at either range.

That being said, having a high IAC can have an off idle cough (ESP with larger TBs). When the IAC pintle is waaaay off it's seat, that means the TB blade is damn near sealed shut. When you crack the throttle, the airflow really spikes rapidly. It can be really bad for those still running the crappy stock MAF.


I like mine to read as low as possible while still reading SOMETHING. That way the actual throttle blade does almost all the airflow for idle and the IAC can bring just enough to the plate to compensate for the trans, A/C, PS pump, whatever.


And,yes, the ECM can comensate for a vacuum leak to a point. Once the leak gets so bad the ECM runs out of range, that's when the car really starts acting up.
 
#7
Just started it up to see what gives on another chilly morning. Being retired is nice as you can have breakfast and read the paper and still have time to tinker with the toys!
Well started up just fine. Went into fast idle and open loop upon start. IAC started at around 140 and rapidly dropped to about 35. Went up slightly as mode shifted to closed loop but eventually dropped below 20 with idle moving between 825-650. A mystery as to what happened but it seems better now. Thanks for taking the time to comment.
 
#8
Just started it up to see what gives on another chilly morning. Being retired is nice as you can have breakfast and read the paper and still have time to tinker with the toys!
Well started up just fine. Went into fast idle and open loop upon start. IAC started at around 140 and rapidly dropped to about 35. Went up slightly as mode shifted to closed loop but eventually dropped below 20 with idle moving between 825-650. A mystery as to what happened but it seems better now. Thanks for taking the time to comment.
I agree, retirement has it's good points. That is strange how yours ran poorly one day and fine the next. My 87 T loves cool weather! The last few times I run it prior to storage, is the best time of the year.
 
#9
Yes, a mystery. They do love cold weather. I am still dialing it in. DYNO tuned it a few weeks ago to get maximum power without detonation. Thought we had it but at Lebanon Valley track last week got 6 degrees of retard on first run so let off the gas very early. Still did a 12.7 although only 90mph. Tried a few adjustments but still got retard. 110 mph on this run. Called it quits after that. Planning to install the larger stock location intercooler from Precision and convert to a 28 pin connector to facilitate more refined tuning of fuel and timing. Always next year.
 
#11
Yeah, well the tuner told me I would be able to get a better tune when I convert to a 28 I connector. I see it as a process. still, a car that does 12.7 with letting up for the last couple hundred feet I not too bad. Better aafe than orry so I will take it eassy til we get it better dialed in.
 
#13
Yes, of course you are right. However, as an old timer who grew up with carburetors and dwell meters I am just getting into this turbo stuff. My last project was a 66 GS. Took it as far as I could and then finally installed an O2sensor to tame the dual quad setup I got from a Riviera GS. Finally got it to run in the 13's. I am sure I will eventually get to the point you suggest but I am content to learn from professionals for now. The GN's, unlike the GS, are fully capable of destroying themselves if you don't know what you are doing. Still can't get used to a cruiser that runs in the 12's without any effort. Guessing when it finishes it should be in the 11's and still get groceries and go to church. I love these cars.
 

Pronto

You're very kind. Some day it will get you killed.
#14
I too came into TBs with zero knowledge of efi. Even with just a Scanmaster, I and my friends learned some tuning. BTW, you do have a Scanmaster right? The Powermaster is a great tool as it lets you see what's going on. You can record a pass or a ride then review it later. When you see the graphs certain relationships will be visible. You can see the parameters you want to get in and after you do a little adjustment you can go back and see what changes. You can also post the file here and get input. You can also post it to the TT forum and Eric will offer some advise. The best place to tune is the track or if you have a clean road to run wot. It's really not that scary once you see it all in front of you. The mods you have are fully capable of 11s with good tires.
 
#15
I do a lot of work with the Northeast GS/GN club gang. John Csordas Jr. does a lot of turbo work. I think it makes sense for me to use his help to get a data logger, upgrade to a 28 pin connector and insert an O2 sensor. I have the bong drilled and capped. My tuner uses it hen we get it on the DYNO. One thing I'm not sure of. You say the best place to tune is the track. Maybe, but I like the ability to get seven or eight runs in without stressing the running gear and watching the results real time and working with a pro to show me what everything means and how to tune it. I am sure that eventually as my knowledge base grows I will be doing a lot more myself. With the older cars I stepped in fairly knowledgeable as I worked with cars at a Sunoco Station in the Bronx NY while going through college, My first "race" car (if you could call it that) was my 1955 Olds Rocket 88. I ran it in LS/A (L stock automatic) at Westhampton Drag Strip until I went into the army in 1968 and eventually got it to run 17's at 75+ mph. Believe it or not this earned a lot of first places then.
 

Pronto

You're very kind. Some day it will get you killed.
#17
Dynos are a great tool. They can zero in the tune but they really don't show how the engine reacts to the real world of going wot from a dead stop. The tune can be too lean for the track because of the difference in the load from track to dyno which might be what you experienced.
 
#18
You are exactly right. One of the limitations of he DYNO is that all pulls are in drive. The shock of start to WOT is not a factor. At Lebanon Valley this past Saturday I was getting retard in both runs although we had tuned out detonation on the DYNO. During that tune, to correct for a lean condition early in each pull we had boosted fuel in parameter 1 (all gears). Tinkering with parameter 2 was not of any use since all runs were in drive. Of course this resulted in a richer condition later in the pulls than we would have liked but it is what it is. My intention on the third run at the track was to add fuel in parameter 2 (1st gear only) to see if that helped. Unfortunately rain clouds ended the day before I could try it. Another advantage of the DYNO is of course you don't get rained out and you don't have to wait on line. I'm very patient and I enjoy the process. I do love this car. Jut off a two year frame off restoration. It's like 1986 all over again. Here is a pic
 

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