I've got a 99 4-runner, 4wd, with a 5vz-fe motor. While freeway driving between 70 & 80 mph I get a blow-off sound ("pish"), similar to turbo blow-off, every 30 seconds or so. Any ideas?

 

Can`t really say I am not allowed to drive that fast!!

Are you losing any coolant ??

A leak in the heater core might do that as the vehicle flexes

Auto or Manual Transmission??

 

Manual transmission. I recently replaced the heater core about 50k miles ago, though I guess it's possible I botched that job. The blow-off doesn't only occur at those speeds but it only occurs when under load and at 30 second intervals at those speeds. It happens at shorter intervals at lower speeds. I tried revving the engine at the same rpms but the blow-off doesn't happen unless under load.

 

Try a new rad cap.

 

Maybe the turbo fairy came and visited you. I have nothing helpful to add

 

Whaaaat? There's a turbo fairy?

 

So I live in SoCal and my a/c is pretty much always on. But I turned it off for once and found that I only get the blow-off sound when the a/c is on. After I figured this out, I turned it on a few times and found it made the sound every time at the moment I turned on the a/c. So it looks like it could be the a/c compressor or condenser. Anyone else had this issue with their a/c? It's still blowing cold.

 

check the tension on your a/c belt. it's probably slipping a little when the compressor clutch engages.

 

Yeah it normally will not make that noise. There is no pressure anywhere that's "blowing off", so you are probably hearing slipping belt. The tensioner takes a 14mm on the front bolt, just loosen it, then a 14mm on the bottom tensioning bolt. Might have to remove skidplate to get to it.