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Old 08-04-2014, 07:23 AM   #4
95 S_Trucker
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Re: 89 S10 4.3 Need help troubleshooting TBI/IAC Idle issue

Quote:
Originally Posted by 76C10Stepside View Post
Thanks for the suggestions and links (had already read the IAC thread).

Yes, I did a full rebuild on the TBI using a kit for Rochester model 100, 200, 220 and 295 TBIs. Kit included new gaskets, injector filters and o-rings, and new pressure regulator. Kit did not include a new regulator dust seal. I tested the injectors using a D-cell battery (good). The kit diagram and instructions did NOT mention the idle air control (IAC)! IIRC, I removed it before cleaning the throttle body and installed a new paper gasket.

The symptom before I rebuilt the TBI was that at idle, the left bore was dry, and the right bore had a film of gas. When I tore it down, the only sign of dirt/debris was what looked like engine oil in the fuel meter body. I assumed this was oil vented from the crankcase.

Now, the IAC is making clicking sounds when ignition is turned on (engine not running and running). Does this sound like a dirty IAC?

The brakes work fine, so pretty sure brake booster diaphragm is not leaking.

Also tested the fan clutch recently (good), but it is engaged for cold starts and most of the time in general, only rarely disengages.

Coolant sensor: The temp reading has always stayed right on the normal mark, and still does, so i think it's good. Do you agree?
Fuel pump: After rebuilding the TBI, truck ran great on the test runs, great throttle response, and made good power (better than before).

Just went out and tried starting the engine again, and it fired right up, ran to 1800 rpm for 20-30 seconds, then down to 1200. The fact that it starts right up after sitting and today's very low oil pressure sounds to me like it's flooding. Do you agree?
There are 2 coolant temp sensors. 1 for the gauge(on the drivers side cyl head.) and 1 For the PCM/ECM(close to the thermostat housing)
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