cold idle issues

JDSfastGN

Well-Known Member
Ok guys I consider myself pretty savvy with these cars but I need some ideas. Ive posted about this before but haven't found a fix. My 87 does not want to just fire up and idle by itself. It has been this way for years. After a minute of keeping it running it will idle but at around 600 rpm or so. Once its warmed a bit and gone into closed loop it will idle itself up to 1000 or so and be fine for the rest of the trip. I have reset the IAC 100s of times lol to no avail. I can up the idle enough to get it to run but then my closed loop idle is 1500 or so which obviously isn't gonna work. I have tried 3 different delphi and delco IACs, TPs(set to .42) swapped coils/modules, plugs, wires, ecms, chips etc... This has been ongoing for 8+ years and is present even after rebuilds and HG repairs etc.. So I rule out vacuum leaks or anything like that. I will try and post a power logger file of the start up for yall to see as soon as I replace my transmission rear seal. I will say when its warm and in closed loop the IACs are 000. If I adjust the IAC to read the proper 10-20 then the next time i start it up cold, it idles very very low. The cam sensor has been out enough to rule its installation out. Im just frustrated because all 3 of our other buicks fire right up and run normal even after sitting for a week. Any other ideas?
 
I'll be watching your thread, it may have something to do with a chip setting? My Buick idles pretty crappy cold, it won't run by itself till it get warm after a few minutes. I've been through the same parts repairs/replacements as you.

I'll be burning my own chip to see if I can "tune" it out.

Could you swap the chip from one of your other buicks? Just to see if the cold idle improves?
 
Little hole in the plenem for the IAC got some grit in it? You probably have already checked that.

I know your pain. For 10 years had a little rapping noise that only happened during idle in gear or when idle dropped low when the defrost kicked in. Turned out to be a loose bolt for the ac compressor. Even a Buick dealer couldn't find that one.
 
Little hole in the plenem for the IAC got some grit in it? You probably have already checked that.

I know your pain. For 10 years had a little rapping noise that only happened during idle in gear or when idle dropped low when the defrost kicked in. Turned out to be a loose bolt for the ac compressor. Even a Buick dealer couldn't find that one.

it has been cleaned and about 5 years ago was ported out by Steve Monroe. It was blasted and clean as a whistle when i got it back, but maybe there is a crack or something somewhere. The blms are 128+- 3
 
Is your coolant sensor reading correctly? Your cold start fuel is based on CTS(coolant temp sensor), your cold start air is IAC.

If your iac reads fine hot idle 15-20 in park.. then either its not going in far enough in to provide enough air.. or???

Does the car seem rich when this low idle happens? Make sure your fuel pressure is 37-38 psi line ON.
 
Is your coolant sensor reading correctly? Your cold start fuel is based on CTS(coolant temp sensor), your cold start air is IAC.

If your iac reads fine hot idle 15-20 in park.. then either its not going in far enough in to provide enough air.. or???

Does the car seem rich when this low idle happens? Make sure your fuel pressure is 37-38 psi line ON.

power logger shows the temp as accurate, the idiot light on top of the intake is broken but that was a recent issue and it has worked fine in the past. The IACs are not good warmed up, they are 000 once warmed up. If I set it up to where they read 15-20 warmed up in park, the car will idle at 300-400 rpm and stall the next morning when its cold and I'm forced to two foot it to keep it from stalling until it goes into closed loop. The car does not smell rich or anything and the WB shows low 12s up to low 13s while warming up. Fuel pressure is 37-38 as well.
 
Is it an original throttle body? Maybe the throttle shaft is moving around, or something is wrong with the IAC casting or passages.
 
Is it an original throttle body? Maybe the throttle shaft is moving around, or something is wrong with the IAC casting or passages.

its a stock throttle body that was worked over and rebuilt by Steve Monroe with new shaft seals etc... I may swap to a stocker just to see what it does.
 
i don't remember exactly but i think it starts out at 150 and works its way down until it hits 000. Ill have to get a PL log, but the turbo is off so i can port the wastegate and i need to install a new rear tranny seal tonight, ill see what i can do tomorrow
 
My question would be if the iac is at 150 it should be fully retracted. If you have a spare iac and throttle body mount you can simply plug it in a verify it's operation
If the iac is fully retracted then the idle should be up
Note the word "if" :)
 
Looking at your sig, you have a LS1 mass air? If so, do you run a Translator? Are the settings right? Ls1 is a 3.5 so I think the setting should be 0 if I am not mistaken.

Just a thought

Prasad
 
Looking at your sig, you have a LS1 mass air? If so, do you run a Translator? Are the settings right? Ls1 is a 3.5 so I think the setting should be 0 if I am not mistaken.

Just a thought

Prasad

Yeah i have gone from an LT1 to an LS1 and yes the translator is set correctly. I have also swapped translators with ones from our other cars to see and there was no change
 
When i turn the key to the on position,engine off the IAC on the scanmaster reads 150.

After starting the engine the IAC drops rapidly to 100 and then continues dropping a number each second until it gets to 80 then it drops a number every 3 seconds until it reaches my set point of 22 on the IAC. The engine idles very good during the time the IAC is making it's adjustments down to normal idle / engine temp.

IAC 22 and TPS .42 at normal engine temp. BLM's at 128 idle and cruise.

This is with the temps in the lower 30's here in Ohio.

Since i do all my driving at night i make my adjustments to the IAC,TPS with the headlights on since there is a difference in voltage with the lights off and will effect the readings.
 
As you increase load the IAC increases. Example you turnon lights, turnon the AC, cooling fans kick on, etc. This is why base IAC numbers should be above zero.. anything is fine as long as not zero.

Coolant temp will vary IAC reading as the IAC opens to allow more air in and raises the idle to warm up the motor. That is why I asked about the coolant temp sensor and its reading when cold. When cold.. the CTS= ambient temp. If CTS=ambient.. then its an IAC issue plain and simple.

IAC issue = bad IAC, bad mount, computer, chip.

PS.. I have never had success with non-delco IAC's. It should be black in color.
 
its a stock throttle body that was worked over and rebuilt by Steve Monroe with new shaft seals etc... I may swap to a stocker just to see what it does.

Have you had this problem since it was "worked over and rebuilt"? After everything you have checked, changed and swapped wouldnt it be good to go back to the core of the problem: the housing i.e., the throttlebody itself and see if thats the issue. Let us know.

Very curious about this one........Subscribed.
 
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