Strange electrical issue

[1998_K1500_Sub]

Check gauges does come on with the battery light.
Its all the way back to key off, not removal, though.
It doesn't need to cool down I can just restart it immediately.
I have replaced both the oil pressure sensor and the relay, still stalls.

I think @docstoy is onto your problem. Since someone messed with the TBI idle screw (and presumably changed the air bleed through the blades), the ECU has the IAC positioned in a different spot ("IAC count") than it should be by design. See my earlier post about "IAC counts" in the service manual.

If you get the TBI's throttle blades adjusted to where they belong, and the IAC counts where they should be at idle, your problem my disappear.

By DISCONNECTING the IAC as I suggested, you'll be able to tell if the surging / loping / dying is due to the ECU pumping the pintle in / out trying to (ineffectivetly) control the idle.

I've had a similar problem on my 1998 Honda V6 after some "Honda Factory Tech" messed-up the idle setting on the throttle body.

 

[bogus]

When it stalls, does the "check gauges" light come on?
Not the "Check Engine" light.
The "Check Gauges" light.
They are not the same.
When it stalls and you try to crank it again are you going all the way back to key off/ key removal before you try again?
When it stalls will it restart after it cools down for a while?
I suspect you have a dual intermittant heat related failure between the fuel pump relay and the oil pressure sensor.
Its a two path system where the truck starts off of the fuel pump relay and once you have oil pressure the fuel pump runs through the oil pressure sensor.
If you have an intermittant with the oil pressure that circuit reverts back to the fuel pump relay.
Its the on and off cycle that causes that little tiny coil mounted contact in the relay to weld itself together and then unstick and reweld itself.
Pull the fuel pump relay and look for slightly brown overheated plastic.
Go to NAPA, get two 30 amp Echlin fuel pump relays.
One for a spare.
If that new relay cures the problem you are halfway there.
Now you need to replace to oil pressure sensor too.

I can actually start the truck up without putting key to off or removing

 

[bogus]

I think @docstoy is onto your problem. Since someone messed with the TBI idle screw (and presumably changed the air bleed through the blades), the ECU has the IAC positioned in a different spot ("IAC count") than it should be by design. See my earlier post about "IAC counts" in the service manual.

If you get the TBI's throttle blades adjusted to where they belong, and the IAC counts where they should be at idle, your problem my disappear.

By DISCONNECTING the IAC as I suggested, you'll be able to tell if the surging / loping / dying is due to the ECU pumping the pintle in / out trying to (ineffectivetly) control the idle.

I've had a similar problem on my 1998 Honda V6 after some "Honda Factory Tech" messed-up the idle setting on the throttle body.

Removed it when running. Engine rpm is at 1550-1600 and holding.

Has a tiny sputter but it's unpredictable

 

[1998_K1500_Sub]

Removed it when running. Engine rpm is at 1550-1600 and holding.

Has a tiny sputter but it's unpredictable

There you go

Now, go back to the service manual and get that TBI idle adjustment dialed-in, per GM instructions.

Then check that the resulting IAC counts are where they should be, as given in the service manual.

 

[bogus]

I think @docstoy is onto your problem. Since someone messed with the TBI idle screw (and presumably changed the air bleed through the blades), the ECU has the IAC positioned in a different spot ("IAC count") than it should be by design. See my earlier post about "IAC counts" in the service manual.

If you get the TBI's throttle blades adjusted to where they belong, and the IAC counts where they should be at idle, your problem my disappear.

By DISCONNECTING the IAC as I suggested, you'll be able to tell if the surging / loping / dying is due to the ECU pumping the pintle in / out trying to (ineffectivetly) control the idle.

I've had a similar problem on my 1998 Honda V6 after some "Honda Factory Tech" messed-up the idle setting on the throttle body.

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[1998_K1500_Sub]

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^^^ Dunno what this is, but it ain't workin' for me.

Ain't nev'R seen it on GMT400, nohow.

 

[bogus]

There you go

Now, go back to the service manual and get that TBI idle adjustment dialed-in, per GM instructions.

Then check that the resulting IAC counts are where they should be, as given in the service manual.

^^^ Dunno what this is, but it ain't workin' for me.

Ain't nev'R seen it on GMT400, nohow.

I found the base idle chart on the manuals but no direction on how to adjust the factory screw. I had to rely on a YouTube video.

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My engine rpms remain high when trying to adjust the screw. I did everything he said. Man, I'm so lost on this

 

[1998_K1500_Sub]

Check that your new IAC's pintle design is the same as the former IAC (which I assume was the OE IAC).

The pintle isn't common across all engines; different designs are used. The ECU will expect the pintle to have a certain design (as the design impacts the airflow as a function of pintle depth into the air bleed orifice in the TB). An incorrect pintle may lead to idle controllability issues such as yours.

 

[1998_K1500_Sub]

Here's an example of a table in one of the GM FSMs that shows the "typical" IAC position.

The TP sensor values are provided too. You can't use these to dial-in the idle screw, but you should see "0%"

This table IS NOT for your vehicle. Search your FSM for similar information.

You must be registered for see images attach

 

[bogus]

Are you sure your IAC is proper for your vehicle?

Do you have an air bleed somewhere else?

I'm positive it's the right IAC.
The oil pressure surges in synchronicity with the tachometer btw