89 350 tbi problems

[Chevyguy]

Don't forget to preset the IAC valve at 18mm. before you install it.

Clayton

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[Vbb199]

Don't forget to preset the IAC valve at 18mm. before you install it.

Clayton

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.708"
From where?

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[Vbb199]

Your current symptoms have uncovered another issue. Even with the IAC fully closed, the base idle speed should be high enough to keep the engine running. It sounds like the idle stop screw needs turned in a little bit.

My question is, how is it the truck ran for many many years without the tbi being even touched, then sat for 5, and after a lot of hassle I got it running again in the place it sat all that time, and now all of a sudden the baseline idle isn't sufficient and I have to adjust before the IAC is factored in?
No sarcasm intended, I have a open mind to suggestions.

Dad said when he dropped the crate motor in, he literally just plopped the old intake with the tbi attached right on top of the crate motor, he's never touched the tbi in his life.

The order goes as follows:

Truck sat for 5 years

I changed fuel filter and clear out fuel lines, new battery, take carb cleaner and clean out Injectors enough for them to spray sufficiently enough for the truck to run in the place it was resting.

I parked it at my house

I sea foam the top end, bottom end, and gas tank.

Truck gets serviced by me, I do new fuel filter, new iginiton, brakes, oil, filter, trans filter and fluid, and I overhaul JUST the top end of the tbi.

Truck sits for weeks afterwards

I go to fire it back up, truck won't run right, very high idle, but runs fine in gear.

Last night I overhaul the ENTIRE TBI unit, and install it
High idle still exists, now truck is stuttering to stay alive in gear.

I replaced the IAC, went thru the reset gambit to set it in relation to the throttle plates, now truck doesn't even run at all with plunger all the way extended (or closed off)

Bounce some ideas off me someone, what dimension am I missing here?

@Arkansas_V8 said himself, it's just a tbi, only so much that can go wrong, and I whole heartily agree, but im learning how to diagnose and troubleshoot tbi as we speak.


Truck ran its absolute Best (and that's figurative) when it was idling higher, and idling fine in gear.
But there was a poor power output.


Dad said back in its day, when he dailyed it, he could stomp it from a dead stop at idle and boil the 31's WITH posi.

I have ABSOLUTELY no doubt in the engine itself, as I said, it's a 20k mile motor.
But sitting 5 years without so much as a fire up has done alot of harm to the fuel delivery system, and everything else on the truck.

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[bucket]

My question is, how is it the truck ran for many many years without the tbi being even touched, then sat for 5, and after a lot of hassle I got it running again in the place it sat all that time, and now all of a sudden the baseline idle isn't sufficient and I have to adjust before the IAC is factored in?
No sarcasm intended, I have a open mind to suggestions.

Dad said when he dropped the crate motor in, he literally just plopped the old intake with the tbi attached right on top of the crate motor, he's never touched the tbi in his life.

The order goes as follows:

Truck sat for 5 years

I changed fuel filter and clear out fuel lines, new battery, take carb cleaner and clean out Injectors enough for them to spray sufficiently enough for the truck to run in the place it was resting.

I parked it at my house

I sea foam the top end, bottom end, and gas tank.

Truck gets serviced by me, I do new fuel filter, new iginiton, brakes, oil, filter, trans filter and fluid, and I overhaul JUST the top end of the tbi.

Truck sits for weeks afterwards

I go to fire it back up, truck won't run right, very high idle, but runs fine in gear.

Last night I overhaul the ENTIRE TBI unit, and install it
High idle still exists, now truck is stuttering to stay alive in gear.

I replaced the IAC, went thru the reset gambit to set it in relation to the throttle plates, now truck doesn't even run at all with plunger all the way extended (or closed off)

Bounce some ideas off me someone, what dimension am I missing here?

@Arkansas_V8 said himself, it's just a tbi, only so much that can go wrong, and I whole heartily agree, but im learning how to diagnose and troubleshoot tbi as we speak.


Truck ran its absolute Best (and that's figurative) when it was idling higher, and idling fine in gear.
But there was a poor power output.


Dad said back in its day, when he dailyed it, he could stomp it from a dead stop at idle and boil the 31's WITH posi.

I have ABSOLUTELY no doubt in the engine itself, as I said, it's a 20k mile motor.
But sitting 5 years without so much as a fire up has done alot of harm to the fuel delivery system, and everything else on the truck.

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The base idle issue wasn't evident before because the IAC valve did a good job of controlling the idle speed. The base idle wasn't meant to be adjusted at all, it would have had a plug covering the adjustment screw when new. But the throttle shaft wears over time and the idle stop screw becomes slightly out of adjustment. Since the tamper-resistant plug is already missing, somebody has done it before.

 

[Vbb199]

The base idle issue wasn't evident before because the IAC valve did a good job of controlling the idle speed. The base idle wasn't meant to be adjusted at all, it would have had a plug covering the adjustment screw when new. But the throttle shaft wears over time and the idle stop screw becomes slightly out of adjustment. Since the tamper-resistant plug is already missing, somebody has done it before.

It's not missing actually, I just did a little investigation and figured out it was hiding behind the tamper resistant plug

But your statement answers alot.

My dad told me back in the day when she ran like a champ, it always idled kinda higher than your standard sbc 8-900 range.

So that explains that.

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[Vbb199]

So maybe tomorrow, I'll go and exchange the IAC for a new one, put the Ecm in diagnostic mode so plunger extends all the way out, then start adjusting the idle screw until the truck will run with the IAC unplugged.
From there, (correct me if I'm wrong Andy), I can plug the IAC back in, and it should meter the idle properly.

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[bucket]

So maybe tomorrow, I'll go and exchange the IAC for a new one, put the Ecm in diagnostic mode so plunger extends all the way out, then start adjusting the idle screw until the truck will run with the IAC unplugged.
From there, (correct me if I'm wrong Andy), I can plug the IAC back in, and it should meter the idle properly.

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Yeah, that should be the proper way. Personally, I'd just give the screw half a turn and install the new valve. Then cycle the ignition a few times and start it up.

 

[Vbb199]

Yeah, that should be the proper way. Personally, I'd just give the screw half a turn and install the new valve. Then cycle the ignition a few times and start it up.

Is the adjustment that sensitive?

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[bucket]

Is the adjustment that sensitive?

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Yep, similar to a carb.

 

[Vbb199]

Yep, similar to a carb.

Excellent, I'll try asap, and post results.

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[Chevyguy]

.708"
From where?

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It's adjustable, the measurement comes straight from my factory manual. Some aftermarket IAC Valve installation instructions also list it.

Clayton

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[Vbb199]

So, installed the new IAC, put the Ecm in diagnostic mode, turned the key on, let the IAC plunger go all the way out, unplugged it, and manually set the idle, kept having to open it more and more and more (3 turns) until the truck finally stumbled to life and started adjusting itself.....

Turned the key off, reset the Ecm with a battery unhook, plugged the IAC back in, turned the truck on, it ran!
But was idling really high, turned the idle back while it running.... Trucks idling at about 800, I don't have a tach right on hand, but it sounds about like 8-900.
So that solves that... But now, boy does she stink like old gas more than ever

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[Vbb199]

Update

I got it running fairly good, but I had a check engine light, truck was running rich anyway....
Went into diagnostic mode and checked the code.
It was

Flash x3 (pause) flash 3x which according to Haynes is "87 only" the map sensor....


I check my vacuum line, I forgot to hook it to the tbi [emoji52]

Hook it up, now truck is running like ass again but not running rich anymore.

(stupid question) am I to assume the map sensor is the blame for this?

The sensor itself was hooked to the Ecm, but the vacuum line was not hooked to the tbi.

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[bucket]

It set the code 33 because the sensor was out of range for what the engine was doing (no vacuum).

May need to do an idle relearn with the MAP hooked up.

Also, if the gas is that old and crappy, it can make it run poor and unstable too.

 

[Snoots]

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