C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

IAC valve question

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Old 07-23-2010, 08:59 PM
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klug932000
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Default IAC valve question

hello all,

after reading some posts to see if i can identify simular problems to mine (85 not starting) and see what the solutions were from members, ive narrowed it down to a vac leak, throttle bodys dirty or the iac valve. i took the throttle body off and cleaned it and i also took the iac valve off.

Questions;
is the needle suppose to have play from side to side

if i test it by plugging it in and turn the ign it goes out and the needle pops out, is this normal

i put it back in and it starts to thread but after a few threads it just turns without going deeper or tighter, once again is this normal

thank you all for reading, if any of these things are bad ill order a new one right away
Old 07-23-2010, 09:45 PM
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BADDUCK
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IIRC the pintle rides on little worm gears. You may be able to reinsert it and reset it but the gears will have to engage. Use light pressure and then reinstall and try the valve reset procedure.
Old 07-23-2010, 09:58 PM
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hooked073
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I hate to say this but none of these will cause a no start. maybe hard and poor running but car will start. Badduck is right put the pintle in without a lot of force unles you will screw it up.
Old 07-23-2010, 10:36 PM
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JAKE
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Yes, it normal for the pintel to pop out under those conditions. Just re-insert it using hand pressure and a rocking motion. It takes a bit of forced, but as long as you're JUST USING hand pressure you'll be fine.

L98s and LT1/4s use different procedures for resetting the IAC. For the LTs just partially depress the accelerator pedal and start the engine. Let it run for 5 seconds or so then shut it down. Re-start the engine and the PCM will have learned the new IAC pintel setting.

L98s involve jumpering the ALDL (Assembly Line Diagnostic Link) and is a bit more involved.

If your idle is still high, first make sure the engine has entered Closed Loop which means the engine has had to run for a few minutes so that all the needed parameters have been met for Closed Loop operation.

A few guys on another Forum are having the same problem right now, dealing with that "slightly open" wording. Start with MINIMUM opening then go up (more open) from there. You really need a scanner to be able to see the IAC count number. They should be in the 20-40 count range (my preference) but I've never seen a GM spec on IAC counts.

The trick is to GIVE the IAC setting as wide a range of operation to account for the added load of A/C when it's switched on, etc.

Hope this helps.

Jake
Old 07-23-2010, 10:54 PM
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klug932000
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i am also considering fuel pressure being a issue or the timing, i am getting a gauge within a few days to check pressure. a week ago the car was running ok it would go from low rpms to mid rpms i dont know exactly what they were as the display doesnt work. the car started to backfire a bit but still ran and the next day it sounds like it fires once and thats it. so now im starting with maintenance that should be performed regardless if it solves the problem or not (hopefully it does though) i friend of mine forwarded the timing on it so it should be in the correct position, it ran the same when he was there and the day after.

thanks for all the input and comments from everyone
Old 07-23-2010, 11:32 PM
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hooked073
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did he tighten the hold down clamp for the dist. if it was running before and acted up after I would look in this direction. even check the connections at the dist. maybe one pulled out from dist being turned or messed with.

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