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TBI Throttle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.

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Old 01-31-2007, 12:32 PM   #1
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How to test for a bad IAC? also looking for someone withALDL in Portland, OR

I have a 90 suburban with a stock TBI 350 that im tring to diagnose a idle problem on. I was wandering if anyone know how to test the IAC to see if it is bad? Also need to know if someone has aldl in portland that might be able to help me figure this surging issue out. Thanks!
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Taking notes for when i need to rebuild my 350.

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Old 01-31-2007, 01:32 PM   #2
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Watching the IAC counts would be a good way. If there are very large changes in the IAC counts with little change in idle or they zero/climb real high with no change in idle speed, then its likely the IAC is on its way out.
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Old 01-31-2007, 01:35 PM   #3
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is it possible for them to stick?
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Old 01-31-2007, 03:38 PM   #4
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I'm in Gresham. My laptop is broken right now, but if you have access to a laptop, i have the cable and everything. I would be happy to look at it with you.

e-mail me at dewey316 "at" gmail.com
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Old 01-31-2007, 05:54 PM   #5
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Thanks man! I dont really have access to a laptop though. I'll see if my buddy will let me use his but i dought it. Thanks for the offer! id like to do that some time. Do you have a programer also?
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Old 01-31-2007, 06:00 PM   #6
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Yeah, i have a programer and the aldl cables and such, none of that is a problem, just my laptop isn't working, so I have nothing to actualy hook it up to. What part of town are you in?
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Old 01-31-2007, 06:18 PM   #7
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SE near 122nd and powell
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Old 01-31-2007, 06:34 PM   #8
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Thats not too far at all, I'm at 258th and Powell.
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Old 01-31-2007, 07:49 PM   #9
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the IAC will stick if its gumed up. you can block the throttle body with a piece of cardboard and see if the engine clunks out, it shouldnt if the IAC is working properly. you should notice a big difference in the idle if it isnt working correctly since its either letting too much or too little into the engine. you said the engine is a TBI correct? you may want to re-build the throttle body... your gonan be suprised with all the junk your going to clean out of the ports. dont be suprised if you find out the port to your pcv is clogged. and be forewarned, if you do re-build, which i suggest, buy a new spring and diaphram for the fuel pressure regulator. the springs in those damn things is always broken. i just rebuild mine last week, takes about an hour unless you get **** with the cleaning. you can clean the IAC while you have the TB apart as well
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Old 01-31-2007, 10:28 PM   #10
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You can disassemble the IAC and clean the crud off the pintle, but unlike the solenoid type, the GM ones have a stepper motor in them with bearings and everyting, so it takes care to do it without trashing the IAC. It may be better to go ahead and just replace it though if its really old. The only thing you have to do other then that is make sure the IAC passages are clean. A rebuild and thorough cleaning is helpful, but optional if the TBI isnt leaking fuel and the vac. passages are still open.
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Old 04-15-2007, 03:10 PM   #11
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Re: How to test for a bad IAC?

Hey guys. Im still having this problem. I did end up getting a new IAC and got my TB shaft rebushed, and got my injectors/FPR rebuilt all at the same time. It made no differnce in the way it runs. Coud someone elaberate on the iac passages? Im not exactly sure where they go. I know that there is a big hole right above where the tip of the pintle would seat in the base(behind the pass. side "venturie"). But i dont know where else they go and suppose they could still be cloged.


DEWEY..... Still interested in helping me out?
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Old 04-15-2007, 08:04 PM   #12
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Re: How to test for a bad IAC?

If the orafice is clear, then its likely the rest of the passage is as well.

It could also be a fueling issue or a bum O2. Does it do it cold as well?
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Old 04-15-2007, 11:46 PM   #13
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Re: How to test for a bad IAC?

O2 is new and actually is one that i replaced another new one with that i suspected was a defective unit. Dosnt idle as smooth as it should when its cold but no, it never surges at idle in gear while cold.
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Old 04-15-2007, 11:46 PM
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