TBI "High Idle Problem":
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,