Vannin' Home Forums Chevy Troubleshooting Throttle body buzzing - help

Hello everyone. New to the forum. I recently bought a 92 GMC Vandura 2500 (350 TBI) and it has a start stall/crank no start. If i give some throttle, it will start and idle. Intermittently, i can press the throttle, and the throttle body will make a harsh buzzing sound. I cannpt figure out what is causing it.

I also am showong 0psi of fuel pressure...with the engine running. I know, i thought it was a gauge too. Ive tried three... all show 0psi. Ive changed the pump, and the regulator. I can hear the pump running.

If anyone could help me with these two issues, id be very grateful.

Thanks,


-Tim

What about the fuel filter?
What does the spray pattern look like coming out of the injectors?
It should be a fine mist rather than a series of drops.
Obviously, 0psi isn't right, but I think these vehicles are lower pressure like around 12psi or something, so maybe your gauge is for the wrong range and isn't getting a reading?
I've had that problem before and had to use an old-school gauge.

As far as the buzzing goes, the only thing I can think of off the top of my head would be the Idle Air Control (IAC) valve.
It's a roundish stepper motor that plugs into the side of the throttle body.
It can be removed and cleaned, but you have to be careful with it, because you don't want any solvents getting into the housing.

Thanks for the reply!

I changed the filter before doing the pump and regulator. The pattern is hard to see. I can see fuel hitting the back of the throttle plates. It looks okay, but its hard to tell. Ill have to get a flashlight on it.

12psi is normal for these Throttle Body Injected engines. I got a gauge that had a TBI adapter, so i figured it would read it appropriately.

Also, with the key in RUN, i hear clicking coming from the throttle body, and it goes away when i unplug the IAC. Idk if the clicking is normal, or a sign of failure.

I don't remember either of my IACs making a noticeable noise.
It turns out to block the air passage, then backs back in to a certain point when the key is turned on, then when the system is in closed-loop, it makes minor adjustments to keep the idle within a certain range.
You could remove it, but leave the electrical connector hooked up, then turn the key on and see if the valve cone (couldn't think of what to call it. LOL) screws out, then screws back in a little. If it just clicks and doesn't move (acts like it's stripped maybe?), then it needs to be replaced.
Also, while it's out, make sure the valve cone is clean and see if there's a bunch of carbon in the port in the throttle body.
If you start the van with the IAC removed from the port, it should idle high (like it has a vacuum leak).
If you stick your finger in and block the port, the idle should come down closer to normal.

If the IAC moved like it was supposed to, then maybe try the relearn procedure and see if that fixes it?
Just disconnect the battery long enough to for the ECU to lose its memory (a couple of minutes or so)...
Then reconnect it...
Jumper the A & B terminals on the diagnostic connector (Like you're going to read the codes by flashing the check engine light)...
Turn the key on (not to start) for about 30 seconds.
That should make the IAC plunger back all the way out to find its base setting.
Then turn the key off and remove the jumper.

There's more to the entire process which involves setting a base idle and some TPS stuff, but the steps I mentioned should get the IAC to zero out, so that it has a solid starting point.

If you have to replace the IAC, you'll have to do that same procedure on it so the computer doesn't use old settings on the new part and the new part will start at zero.

Dang! Did I really just type all that?