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Old 02-07-2004, 12:38 AM
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TBI "High Idle Problem":

Hello,

New fella here, I have a 87 Chevy crew cab dually w/454 engine. I bought the truck a few weeks back and been trying to get it to run right, here's the problem: The engine act's like "if" it had a choke it would be hung up. The engine idles at a high rate and won't come back down to normal. This truck sat at a house for the better part of a year, and before that it was used to haul trash to the local dump, when I got it my buddy said they tried to crank it and it backfired, when it did the harness for the injectors got toasted. It burnt the insulation off down to where the wires go through the tbi, I'm wonderong if the injectors them selves have been damaged and the whole tbi needs overhaul?

Here's what I've tried so far, this motor has a "heater"? of somekind that's between the tbi and intake, I have replaced both gaskets, between heater and intake and tbi and heater, I was told this is usually the problem, but no dice, so I checked all the vac. lines running from tbi out, found 2 leaking (replaced them) and 1 not even hooked up. Also have installed new plugs, wires, cap, button. It had a real loud "hiss" to it when I drove it home and none of the dash gauges worked. I checked all fuses and found one marked "gauges/idle" was blown so I replaced it and the hiss noise went away, but still no idle.I have also pulled idle air valve, cleaned it and replaced. The only lights comming on in the dash are, seat belt and "choke" I test drove it the other day and the "choke" light came on and went out after a minute or so and the thing idled right down and ran beautiful, got almost home and the light came on again then the "high idle syndrome" happened again and been like this since. Can anyone help? Sorry this is so long but I figured to help diagnose the problem as much information as possible needs to be said. Thank You for your time,

Conoverbandit

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Old 02-07-2004, 12:45 AM
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conoverbandit,
Use a timing light and point it toward the TPI. You should see a nice cone shape to the spray pattern of the injectors. What I think you will find is one or both of the injectors will drip instead of spray gasoline. Replace it and do the test again.
Good Luck
scholman
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Old 02-07-2004, 04:09 AM
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A fuel injected 454.....
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Old 02-07-2004, 05:21 AM
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Last edited by roys63; 02-15-2004 at 07:24 AM.
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Old 02-07-2004, 09:48 AM
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I don't have to use any kind of light, man you can see this thing just dumping the fuel on top of the butterflies, and yes I have noticed a "dripping" action from time to time. I'm going to look for the 02 senser and just make sure it's hooked up. I changed the coolant senser on the intake, did'nt help. Someone told me that these set ups have 2 coolant sensers on them, is this right?
Thanks,

Conoverbandit
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Old 02-07-2004, 11:08 AM
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Theres two sensors but one is for gauge and other is for computer.
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Old 02-07-2004, 01:32 PM
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Changed the 2 wire w/new one, just found the other one. Found wire and hooked up now hopefully gauge will work lol.
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Old 02-07-2004, 08:21 PM
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ttt
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Old 02-07-2004, 10:32 PM
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I know of at least 3 trucks, 350 TBI, that sat for a while while getting motor rebuilt or replaced and the idle solinoid went bad. My truck sat for about a year before I got it. After a motor was installed it idled high too. After about a week of this it idle fine and has ever since. The other two trucks I referred to had to have the solinoid replaced. Hope this helps.
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Old 02-08-2004, 12:49 PM
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Thanks,
I'm starting to think that is the culprit, The IAC, I cleaned it, but I could'nt get back into where it seats to clean that, I will try to come up with something to clean that, and if it still don't work I'll replace it. Thanks,
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