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1991 L98 383 - Cold Start Idle issues

 
Old 03-12-2019, 09:28 AM
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Deepa
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Default 1991 L98 383 - Cold Start Idle issues

All,

Hope everyone is doing well. Been a while since I posted but the l98 383 is running great - once its warm.

On a cold start (outside temps below 50) - the idle hunts up and down from 1400 to 800 for about one - two minutes. It was not an issue during the summer / early fall. Problem started

Normally, no big deal...but...I leave for work at 5:15 AM, live in a dense neighborhood, and have long tubes/true duals/connected right to a corsa...so its rather loud.

It's difficult to drive while its hunting for an idle, and I have to give it more gas then necessary...making it louder for my sleeping neighbors. Idling in the driveway isn't an option either at that time of the morning.

SO...I used to have datamaster...my laptop is junk (buying a new one now) and it wont connect to the car. I need to get my data logging / monitoring up to snuff, but in the mean time, I've tried a new IAC and looked for vac leaks. I found one near the IAC where the IAC manifold/adapter bolts to the throttle body, repaired it, but the problem persists. I also think my new IAC is junk as it was in pieces in the box. I'll replace with the old one or buy another AC Delco one and throw the duralast in the trash where it belongs.

I have not done a base idle reset. Waiting for data monitoring program to see IAC counts...if its even working, etc. I also want to see what the coolant temp sensor is reporting...

Where else could I look in the tune? It's tuned by a local guy but word is he moved his shop to FLA.

Thanks for all of your help. Car runs great once it's warm.

Mike D.
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Old 03-12-2019, 04:41 PM
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htrdbmr
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Did run well last winter or is this a new condition?
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Old 03-12-2019, 07:55 PM
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Deepa
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The engine swap was completed in July 2017, and it was taken off the road for winter in nov 17, so it never got down to below freezing really in 2017. Winter 2018 / 19 was the first time I drove it later than December because the snow came so late this year.
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Old 03-12-2019, 07:59 PM
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wadenelson
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Borrow a smoke machine and smoke the manifold. Sounds like a vacuum leak.
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Old 03-13-2019, 05:02 PM
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Deepa
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Did the base idle reset today after work.

Seems to have helped overall, but need to let it cold soak and give it a go tomorrow.

Talked to the tuner, heís willing to give it a look if needed.

He seems to think it happens when the iac is trying to get to a set position at the cold ambient / coolant temp and it cannot do so, so it hunts for a idle. This could happen if the tables need to be tweaked or the base idle / iac isnít at a normal range.

Thanks all.
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Old 03-13-2019, 06:15 PM
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ctmccloskey
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Do you still have the cold Start Injector on the engine? The ninth injector can fail just like any other, It only comes on a pre-set temperature and helps start the car in the colder weather. If it is there simply unplug the sending unit that powers the injector.

I doubt you would have one of these injectors on a "Built" engine. I had to replace mine but it is typical 1988 Automatic Coupe with 100k on it.


Good Luck and keep us posted! Very curious following here...
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Old 03-14-2019, 12:08 PM
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Deepa
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No cold start injector on the 91s.

Im gonna give it a shot later today.

Going to try to get it hooked up to my new laptop too and see what itís showing.

Thanks.

Mike
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Old 03-15-2019, 07:28 AM
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Deepa
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Base idle reset didnít fix it.

Ill have the tuner look at it when my trucks done
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Old 03-15-2019, 08:33 AM
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My 398 does it, its a winter only problem for me. It was tuned in summertime. What I do is open the throttle screw and reset the TPS to give it more air. I also dont move from the garage until the idle has settled down, if i try to drive with it like that, it will cut off on me at a stop sign.
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