Hello! Possibly a dumb question, but is the IAC valve supposed to buzz when you turn the key ignition to "on" with engine off?

I've been struggling with an IAC code and weird timing/idle issues (until it warms up to operating temperature) for about 2 years, and my poor 1996 4Runner 3.4 5VZ-FE 2wd w/ 280K miles finally started up last week and then suddenly quit. Can't get it to start back up.

Things I've replaced: fuel pump, fuel filter, crank sensor, cam sensor, pcv valve, throttle position sensor, coolant temperature sensor (the one to the ECU under the fuel rail, not to the cluster by the firewall), and the IAC valve itself (aftermarket) about a year ago. A couple months back, I tried hooking up a bluetooth OBDII adapter, which used to work fine and now it doesn't. Bought a wired OBD2 reader last week since I wanted to check codes and thought my bluetooth just went bad, and it doesn't work either, so I pulled the ECU out, and it had a leaking capacitor, and I thought, "Ah-hah!!" Got a rebuilt ECU, and no change. Still won't start, and still won't connect to the OBD reader.

I put the old OEM IAC valve back on just to see if maybe... but for the first time, I noticed when I turn the key to "on" (engine off), the IAC valve buzzes pretty noticeably. I then put the aftermarket IAC valve back on, and it buzzes too, just not as loud. I've never noticed the IAC buzzing before, like ever.

Is the IAC valve buzzing normal and I just never noticed it, or has that leaking ECU capacitor perhaps junked 2 IAC valves now? Hate to throw another couple hundred bucks at a new IAC valve, so I thought I would ask the experts. Any advice or suggestion is welcome and appreciated.

I don't remember if it makes a buzzing sound but I would certainly get rid of the aftermarket IAC. I'd only run an OEM one.

I tried an aftermarket $30 IAC once. It made my engine idle at about 1200 RPM when warmed up so the next week I bought a new OEM one.

That being said, the IAC won't keep it from starting. What WILL keep it from starting is a failed Throttle Position Sensor or TPS. Are you sure it's not the TPS buzzing? That'll kill the engine 10 times out of 10 if it's bad.

I believe the sensors that can cause a no-start condition is the MAF (mass air flow sensor), TPS, Camshaft position sensor and Crankshaft position sensor. I'm not saying to go out and buy them all, there are voltage checks you can do on each of these with a multimeter from the factory service manual first to check.

Did you ever resolve this? The same thing is happening to my 4runner (no-start, ticking under/in throttle body that goes away if IAC is unplugged, can't scan for codes via OBDII port). I've replaced some of the parts you mentioned too. I am just covering all my bases before I spring for a new IAC to see if it solves my issue. Cheers!

I tried an aftermarket IAC for my 2004 Pilot. It did not work. So I sent hours cleaning the original IAC in a dish pan with an asortment of wire& nylon brushes sprays etc to remove the carbon that caused running problems. Tested it with a small 9vdc battery and it clicked!
Reinstalled it and it ran like new at 230,000 miles.
Forget the aftermarket for these delicate , time consuming to install components.

Have you replaced the electric relays in the ingition start system. In my 2004 Pilot it was intermittent and passing reduced voltage when it did work.
The Pilot went to a new home at 240,000 miles and I bought my SR5. My favoite vehicle!