TBI 350 Target Idle Speed

[tayto]

throttle shafts probably need bushings

[MO LS Noobie]

Base idle speed, coolant temp, AC, transmission gear, and engine cranking idle air all factor into the "idle required" rpm

[ralmo94]

Just throwing this out there as I did not notice it mentioned before, but is the coolant temp on the scanner reading correctly? As you probably know the dash gauge has a separate sender than the ECU. Does it flood easy when starting it?

[stew86MCSS396]

The thing that really stands out to me is the IAC is at 0%. First thing I would do is block off the air supply to the IAC, this is the kidney shaped hole next to the throttle blade directly above the IAC valve. Is there any air at all going through that valve? With 0% I there should not be any air at all. If there is air going through that valve then either the valve is bad, wiring, PCM, or the computer just hasn't learned the home position. See post number 6 by TriumphR3 above.

If there is NOT any air going through the IAC valve then you have too much air getting in some place, the most common place is the mounting gasket for the TBI unit, but you already replaced that. I use propane to sniff out vacuum leaks on the engine itself, typically a missing vacuum cap, compromised vacuum line, the PCV valve, or intake manifold leaks at the gasket. You can use carburetor cleaner to do the same thing, but it tends to puddle and is a severe fire hazard. Not being able to see the fuel trims makes things harder but you should be able to hear a vacuum leak because the engine will smooth out and speed up.

Do you have access to another scanner? There are a couple of other things that your scanner is showing but that IAC percentage is the first place I would look.

There was another forum post with a similar issue and the fix turned out to be the IAC was wired wrong. Idk how that mysteriously happens if no one messed with the wires...

Battery volts could be a little concerning. Not 100% if TBI has injector offsets vs batt volts and how that would affect idle quality??? That 53% throttle looks unusual too.

[Sledhead2]

I am late to the game, was truck running fine and then just started idling high?

Did you do any work to it and then it started?

Guys here is a left field question, if he cooked his O2 sensor, could/would it cause high idle?

[TriumphR3]

A faulty temp sensor that goes to the ecm can play havoc on idle rpm’s.

[maronielb]

Yes it is coolant reads at 195 on the scanner and it’s a brand new ac delco sensor

[ralmo94]

A faulty temp sensor that goes to the ecm can play havoc on idle rpm’s.

X2.
That's what I was wondering about because requested idle rpm high.

[ralmo94]

Yes it is coolant reads at 195 on the scanner and it’s a brand new ac delco sensor

Interesting

[maronielb]

Trucks always idle around 1k when i first bought it but i didn’t care because inwas going to rebuild the throttle body so i ended up rebuilding it about a year later and it stills idle the same

[maronielb]

Yeah I’m lost this thing has be pulling my hair

[maronielb]

It’s brand new ac Delco sensor and my scanner shows the computer is reading 195 degrees

[maronielb]

I havent messed with the wiring it’s still the factory plug

[maronielb]

Please elaborate on this, where can i get the bushings and it is hard to replace? How can i determine if i even need bushings!

[ralmo94]

I have messed with the wiring it’s still the factory plug

Off the top of my head, idle speed is determined by AC off or on, and Park Neutral, or in gear.Other than that it's temp. Does the air work, and does it have an auto?