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Old 01-06-2011, 10:01 PM
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1994 TBI idle problem...

1994 K1500 350
New Distributer, rebuilt throttle body, new IAC new injectors, timing set...PROPERLY. New PCV , good cap/rotor/wires/plugs, 6500 miles on new engine( Flat tops eddelbrock 3702 cam, 3 angle valve job, headers hi flow cat glass pack) new oxygen sensor. Sometimes idles perfect, other times it will lope till it dies like a vacuum leak. I have searched hi and low for leaks and cant find any. Also- very defined buzzing noise heard in cab, possibly throttle body? any of the things i have done have failed to help the situation. When it starts to stumble if i barely touch the throttle to take it closer to 900 RPMs it will be smooth. NO check engine light... God i wish it would throw one. Please help me!

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Old 01-06-2011, 10:18 PM
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Have you checked the play in the throttle shaft? Grab it and see if you can shake it. It should hardly move. If it has excessive play it will need to be replaced or new throttle shaft bushings installed.
Was the fuel pressure regulator replaced with one that`s adjustable with vacuum compensator? What`s the fuel pressure?
Next is put a vacuum gauge on it when it goes to idling erratic and see what it does. Also check the TBI base gasket for leaks.
Try this test also, disconnect the vacuum line going to the EGR valve and see if it improves the idle. If so the valve is sticking open.
My 4.3 TBI has a load of mods, and it too lopes at idle and no matter what I`ve did I can`t get it to stop. It never shuts off, but the lope is annoying. Finally I just chalked it up to the larger cam.
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Old 01-07-2011, 03:47 PM
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wel today i put another computer in it, and pulled the TBI spacer out and checked the gasket, put back together and it improved a lot. My spacer gasket or somethin must have been screwed up. I have checked the egr before its fine though
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Old 01-07-2011, 05:50 PM
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With all the repairs and mods that have been done ,you should perform a minimum air rate calibration, it calibrates the airflow so the idle speed can be controlled accuratley. It is common practice(was ) to readjust it for customers after they had driven the car for several thousand miles after new, just like re-adjusting the carb after breaking in the motor.
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Old 01-08-2011, 10:02 AM
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How do i do that?
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Old 01-08-2011, 10:23 AM
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warm up the engine to operating temp.shut it off and jumper A and B terminals in the ALDL (connector under dash) then turn on key and go under hood and unplug the Idle Air control.Start engine, adjust the base idle screw on the throttle plate until about 500 rpms is reached then verify the TPS voltage is at .58 volts, if not you will need to adjust it also.
There is a plug over the throttle plate adjustment screw that will need be removed to access the adjustment screw for this process. I would remove it if need be. If the adjustment proves to be within spec it may not need to be removed.
After the adjustment shut off the motor,plug in the IAC, remove the jumper from the ALDL and restart engine.After that it should be good to go.
Make sure your vehicle is not OBD 2 as the procedure is different and you dont want to attempt jumping anything on the connector unless you are sure of what you are doing.
The ALDL stands for assembly line diagnostic lead.look here so you know where you are at:
http://www.aldlcable.com/
This will clear up any questions about the connectors.
Being a 94 pickup it probably is not OBD 2. But be sure.

I am assuming that the timing has allready been PROPERLY ADJUSTED before this procedure.
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Old 01-08-2011, 04:50 PM
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sounds good. which connectors are the A and B? and yes it is OBD I and the timing is set properly for sure.
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Old 01-08-2011, 05:09 PM
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that would be PINS A and B. look at the webpage that i posted.It is partway down the page. It will show the pins .Good Luck
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Old 01-08-2011, 05:13 PM
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great site. thanks will do now.
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Old 01-08-2011, 05:25 PM
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going against everything you are supposed to do when adjusting these trucks i have found my best results are found by adjusting the idle while running(reving up between adjustments slightly to see how it brings itself down to idle). I tried jumping the aldl plug, disconnecting IAC and starting it. it idled about 1500 rpms. i couldnt turn it down enough.
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Old 01-08-2011, 05:27 PM
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Quote:
Originally Posted by shane.,herold
going against everything you are supposed to do when adjusting these trucks i have found my best results are found by adjusting the idle while running(reving up between adjustments slightly to see how it brings itself down to idle). I tried jumping the aldl plug, disconnecting IAC and starting it. it idled about 1500 rpms. i couldnt turn it down enough.
Well Good luck with that.
Sounds like the IAC did not close the pintle into the seat.You can see the tip by looking down the side of the throttle body where the IAC is. Jump the connector THEN turn on the key, then go out under the hood, look to see that the pintle is blocking the passagaeway and THEN UNPLUG it. Then restart.
Also...was the engine previously warmed up? I checked my instruction, it was correct. If you followed the instructions and had a fast Idle like you said then something else is wrong.

Last edited by latech; 01-08-2011 at 05:33 PM.
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Old 01-09-2011, 10:28 AM
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thats what i was thinking. i will check.
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Old 01-09-2011, 10:36 PM
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I think if you change the cam and mods you need a new chip burnt. I think if you look at the cam it say's you need a tune to get the best performance! Also I would go Here to get support! www.fullsizechevy.com www.tbichips.com

Craig
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Old 01-10-2011, 10:47 AM
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i have been told the 3702 is the closest to stock cam u can get...
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