I have a rough idle when I start after I leave my 88 305 overnight.
it needs to be revved 3-4 times right after I turn the key or it will sputter and die.
then the idle is choppy for the next 5 mins or so then like a switch turning on it smooths right out and runs well.

recently I started it up and then bridged my ALDL for field service mode when It was idleing rough and that cleared it right up.
I dont understand what that could have done other than bypass some sensor or computer function that is causing this problem.

could someone please Identify the problem as I am unfamiliar with computer functions in field service mode.

thanx in advance

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88 WS6 T/A 305 TPI--
K&N,Air foil,hypertech chip, thermostat+fanswitch
free mods, dynomax catback, urethane motor+trans mounts,
SSM SFCs, Bilsteins
very trick homemade ramair, Accel 300+ ignition system.
Planning: hedman 1-5/8 longtubes, NOS 150 plate, world 305 heads, replace the "peanut"! and other susp. mods.
check it out at:
http://www.geocities.com/transam617

 

Does it smooth out when it goes closed loop, or is there no correlation? Maybe leaky fuel injectors, leaky fuel pressure regulator?

Tim

 

closed and open loop do not incurr any difference. its just when I start it up and the idle is bad. then when I bridge the ALDL the idle smooths out. from there I can see it go from open to closed loop and there is basically no difference. if I pull the bridge before it gets warm or whatever, the idle gets sh@@ty again.
I am thinking that bridging the ALDL takes some sensor out of the loop or puts the comp into limp home or something I just cant figure out what. if I knew I would know what my problem is instantly.

I might agree with you about the leaky injectors or regulator thing but it seems more like a vacuum leak to me that goes away with time.

hmmm this ones a doosey!

 

88,

Installing a jumper in the ALDL after the engine is running will force the ECM into Backup Fuel Mode. This provides about a 12:1 fuel mixture as opposed to the design 14.7:1. If the fuel is lean on startup, the ECM will not interpret this until the oxygen sensor is hot enough to begin signalling the ECM. Until this time, the engine is operating on Block Learn Memory fuel tables that have been generated by the PROM parameters and the Integrator function of the ECM.

It sounds as if you have a lean condition until warm enough for Closed Loop Mode, then the ECM and O2 sensor take over to correct the mixture rates. Check vacuum reading and for leaks if the readings are low, fuel pressure at idle, TPS voltage, throttle minimum air position, CTS readings, MAT sensor readings, and intake system and ductwork leakage.



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Later,
Vader
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"I'm'a do Things My Way - It's My way or the Highway."
Adobe Acrobat Reader

 

YES!!!!
that is EXACTLY what I wanted to know.
thank you so very much vader and may the force be with you.

 

my 86 firebird was doing the same thing.
how long has it been since you replace the OX sensor? Thoes things go out quite offen. If the Ox sensor malfunctions it will some times work and other times wont work, that the "on, off like of the idle"

for the couple of dollors that the Ox sensor. its not a bad Idea to replace it any way.
(a new Ox sensor will improve performance)



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Chuck
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I'm not shy, I just
observing my prey.