TBI idle problems

[Trigger_guard]

So, I'm messing with an old 1 ton square body with the 5.7 TBI.

***** thing don't wanna idle. It just barely hangs in there. Couldn't find any obvious vacuum leaks.

Pulled the air cleaner and it's sucking air like a hoped up Hoover. Sounds like a jet plane. The driver side injector is definitely squirting more fuel than the other. Too much it looks like cause it's just laying on the butterfly.

Took it down the road and runs about as bad as a tbi should.

Once I got it hot then it idled real fast. Like 2500 fast.

If y'all have any suggestions I'd be appreciative.

Sent from my SM-N960U using Tapatalk

 

[MIHELA]

Did you clean the IAC valve?

 

[PlayingWithTBI]

The driver side injector is definitely squirting more fuel than the other. Too much it looks like cause it's just laying on the butterfly.

Is it spraying or dripping too? If dripping, you may have a leaking O-ring or you need to send them in, get them cleaned and calibrated.

Did you clean the IAC valve?

X2

 

[Trigger_guard]

The driver side squirts, the passenger drips, at idle. The both squirt good when you hit the throttle. But that brings a lot of hesitation


I don't know 2 things about tbi stuff. But I'll find the IAC and I'll clean it

Sent from my SM-N960U using Tapatalk

 

[PlayingWithTBI]

But I'll find the IAC and I'll clean it

You'll need to calibrate your TBI too. If not calibrated, you run the risk of burning up the stepper motor in the IAC. Here's an old .pdf but it explains how it works, where it is, and how to do the initial calibration.

TBI tuning-website - Tuning the TBI.pdf

 

[Schurkey]

Wild Guess: One injector is blowing excess fuel, because the other injector doesn't supply enough, and the O2 sensor thinks the engine is lean. The engine runs like crap, so the IAC is trying to lift the idle speed by going wide-open.

Get the injectors to squirt properly, all the problems go away.

Grab a propane torch, DON'T light it, and aim some propane in the venturi that's not getting as much fuel. See if the engine runs better.

Any misfire on the driver's side will also fool the computer into thinking the mixture is too lean. Verify cranking compression, plugs, wires, cap, rotor, etc.

As usual, connect a scan tool, look at the data stream. Commanded idle vs. actual idle, O2 sensor readings including cross-counts, and anything else that seems noteworthy.

 

[JakeLikesVans]

I spent a lot more time that I ever wanted chasing down little issues like this one. Ended up just throwing in the towel considering mine only surges a bit while in park and hot. Anyway, yeah try calibrating the IAC valve which could help a lot after you get those injectors either cleaned real good or replaced entirely. Definitely should not be dripping. That's a big problem. Double check you don't have any exhaust leaks at the header (I'm guessing you don't because it sounds like the stock iron headers are there?). Also, on the front of the TBI unit (looking at it from the radiator) on the base to the right there's probably a little rubber plug that covers the butterfly "idle" adjuster screw (T20) but don't mess with that until you've tried everything else and ONLY during the initial re-calibration of that IAC valve. Just start googling some stuff...you'll be fine