454 Idle Help
Printed From: West Coast Fieros
Category: Technical Topics Forum
Forum Name: Technical Questions and Discussions
Forum Description: Got a technical question about your fiero? ask it here.
URL: http://www.westcoastfieros.com/forum/forum_posts.asp?TID=2615
Printed Date: 23 November 2024 at 10:06am
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Topic: 454 Idle Help
Posted By: Romeo
Subject: 454 Idle Help
Date Posted: 03 August 2011 at 2:05pm
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Alright, I recognize this is the Fiero forums, not big-ass truck forums, but still, they're both GMs, and I'm hoping one of the TBI guys might be able to help. My 454 was idling stupid high (Around 2000RPM) before I noticed the IAC had been disconnected. Since re-connecting it, the truck has settled down to about 1500RPM, which is still too high to even put it in to AirCare. I've checked for vacuum leaks, and there arn't any. I've also tried manually forcing the idle set screw lower (Which is a challenge in and of itself) and even with the throttle blades closed completely, it still wont go down below 1500RPM. It had a code for low throttle position voltage before, but that's gone now, for what it's worth, and no new codes have taken it's place. Any ideas on what's causing it to idle so outrageously high? ------------- Never shift into reverse without a back-up plan. |
Replies:
Posted By: Dr.Fiero
Date Posted: 03 August 2011 at 8:49pm
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Only one thing: Vac leak. First thing to do is force the IAC all the way closed. Key off, jump the A/B pins (this IS an OBD I truck right?!). Key on. Wait about 20 seconds, then unplug the IAC. Key off. That'll drive it all the way in. Lowest possible setting. Listen at the IAC while it's going in (maybe grab it too) and make sure it's really moving. Now start it and see where it idles. Still too high? Stick your fingers up under the EGR pod (if you can) and push it up. See if it feels 'clean' as it goes up. It should also stall the engine. If the idle doesn't change a LOT when you push up on the pod, it's probably 1/2 stuck open. Start there and report back. |
Posted By: Romeo
Date Posted: 03 August 2011 at 11:17pm
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Sorry, should've mentioned, I already checked for vacuum leaks (They were quite common on the TBI 454), there are none. I'm beginning to suspect it is the IAC. Haven't tried jumping it yet, but I know when I helped "plug" the IAC (Wrapped electrical tape around the tapered section of the valve, closing it off more), the idle settled right down. I actually have the EGR pulled at the moment, however, so it wont be that either. I'm thinking you're spot on with the IAC though. I'll try jumping it tomorrow. ------------- Never shift into reverse without a back-up plan. |
Posted By: Dr.Fiero
Date Posted: 04 August 2011 at 5:20am
Understand that when I say vac leaks... that includes a sticky IAC. Maybe if I say 'uncontrolled air flow'. Also, just because you checked - doesn't mean you found them all! |
Romeo wrote:Posted By: Romeo
Date Posted: 04 August 2011 at 12:29pm
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Well brother, I may have missed a vacuum leak, but in the mean time, the IAC was the way to go. It doesn't adjust back all the way, so there's a constant, large supply of air rushing past. I'm going to replace both the IAC and it's connector (The connector ain't looking so hot...) to be safe. In the mean time, my electrical tape solution seems to be holding up just fine. Thanks for your help, Doc. ------------- Never shift into reverse without a back-up plan. |