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Fast Idle Chevy 350 TBI

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Anonymous Poster

Jun 20, 2009, 6:16 AM

Post #1 of 2 (5903 views)
Fast Idle Chevy 350 TBI Sign In

I have a 1992 chevy 1500, 5 speed, 4x4. Recently switched engines from 4.3 to 350 TBI. Engine block is 1995, all electronics are 1992. It has a 350 TBI engine, computer, injectors, throttle body. The EGR valve is a 350 (from a salvage yard) but moves up and down so vacuum will operate it.

It still have the 4.3 wiring harness and the 02 sensor is a 4.3. I have tried the suggestions for locating any leaks by spraying starter fluid/WD40 and doesn’t change idle. I can reduce the fast idle some by adjusting timing but then it loses power and cuts out occasionally.

Before changing the AC did not work --- now it does. There are no lights on, no codes.

Any suggestions for this fast idle problem?

Thank you.

Veteran / Moderator
Sidom profile image

Jun 20, 2009, 7:39 AM

Post #2 of 2 (5898 views)
Re: Fast Idle Chevy 350 TBI Sign In

Well a quick easy test you could do to point you in the right direction would be to block off the idle air bypass on the TBI unit. There'll be a hole by the IAC (round or B shaped) completely seal that while the engine is running (it's pulling vacuum so what ever you use, make sure it can't get sucked in there), it should drop to base idle which is around 400 rpm.
If is does your problem is computer controlled, if it doesn't then you are getting air in there....somewhere.....

(This post was edited by Sidom on Jun 20, 2009, 7:41 AM)

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