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Car is an 86' / Automatic, My idle is showing as 8-900 rpm when warm . In Drive it stays at 800 rpm. I tried adjusting it as per the procedure in the FSM. No good. Couldn't get the TPS to .54 , it wouldn't go higher than .27, waiting on a replacement, going to replace the IAC also. My question is, does the ECM and E-Prom control idle speed? The previous owner has installed an aftermarket chip from TPIS. With the screw on the idle backed out all the idle didn't drop at all, I am thinking the speed is controled by the ECM. I know I am repeating myself, but I tried searching and no luck.
Thanks in Advance.
 

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I am thinking the speed is controled by the ECM.
The ECM operates the IAC ( a motorized air leak ) to try and get the programmed idle speeds
does the ECM and E-Prom control idle speed? The previous owner has installed an aftermarket chip from TPIS.
Yes
There are idle speeds programed on the chip.
If it is different on your TPiS chip to stock settings then you will never be able to get it right by adjustment unless you know what the current setting on chip is

. With the screw on the idle backed out all the idle didn't drop at all,
Did you have the IAC disconnected ?
 

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I have a TPIS level 5 chip and come to think about it my idle is the same as yours and I like it with my set up. I also have a super ram.
 

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At that point no. When it was disconnected, I couldn't get it to hold an idle on it's own. I have a new iac and tps I am going to install as soon as the weather warms up. The engine has some work done to the heads, the cam and the intake is a super ram. The previous owner had it done back in 01' as well as the chip.
thanks
 

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Definitely, does.
 

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At that point no. When it was disconnected, I couldn't get it to hold an idle on it's own.
So you have a problem
Adjusting idle with IAC disconnected is same as adjusting idle on a carb engine ;
the amount of throttle blade opening sets base idle
If you can't get it to idle you have problems elsewhere , vac leak maybe?
The IAC is only the the means by how the ECM adjusts idle to suit different cond
FWIW
I am working on a hi idle problem ( its in the tune) in one of my cars
However with IAC disconnected I can adjust idle down flat 400 rpm and that is with a LT4 cam
 

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Vetteoz,
if you get a handle on the high idle problem let me know. Mine starts up at 800 rpm cold and when up to temp races at 1600 rpm. If I disconnect the AFS it drops to 450. Been too cold and snowy here to work on it. I think ECM but still have to check vac lines etc. Once this is fixed I can start cosmetics.
Lew
 

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Vetteoz,
if you get a handle on the high idle problem let me know.
My '87 doesn't flair up it, just won't come down below 1K @ hot idle.
As I said perfect idle with the IAC disconnected , can get idle so low it almost stalls so I know I have a control problem ; not a engine problem
Just for the hell of it I threw a stock '89 memcal in it and it is pulling down hot idle to correct numbers so the idle problem has to in the tune somewhere.
Got to get the time to compare both tunes and see where the difference lies
 

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it is a weird problem, as the engine heats up the idle increases.Seems to be opposite of what it should do. It came on shortly after we bought the car. It would be normal 90% of the time and then started to be 100% bad. I'm thinking I did a mod to the wiring at the ECM when I had the 4+3 in it. I by- passed the ECM to control the OD manually. Maybe I did something then. As I think about it the problem started shortly after that. I have since repaired the by-pass. Maybe I need to shop the junk yards for a ECM. Quite a few GM models used that ECM.
 

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I'm thinking I did a mod to the wiring at the ECM when I had the 4+3 in it. I by- passed the ECM to control the OD manually.
Good point.
There is a ECM input from the auto shifter to tell the ECM whether trans in in P/N so it can adjust idle speed.



Mine too is a 4+ 3 car converted to auto and I did nothing with that input.( is open all the time )
In the past have always had "hot " engines in the car so idle was way higher than stock due to cam.
Now I have " restored" car to stock for sale I have the same problem as you.
Going to play around with that input tomorrow and see what I come up with; things are making sense now

Maybe I did something then. ECM.
Only input from trans to ECM is the signal that tells ECM that trans is in 4th gear , would not have any effect on idle whereas the P/N input does

Maybe I need to shop the junk yards for a ECM. Quite a few GM models used that ECM.
Won't be the ECM , either a input or on the tune
 
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