Hey everyone,

My 2000 4Runner 3.4L 5VZ-FE (Manual gear) dies every once in a while, when I'm about to stop at the light or the idle goes below 500 without dying, then recovers back to normal. I have done these to trouble shoot it: cleaned the MAF, cleaned the throttle-body, changed the throttle controller, changed the Vacuum switching valve, and also checked for vacuum leak.

Any other suggestions you guys might have? The truck could run fine for while then it starts dying or idle below 500 RPM.

Thanks in advance

 

Sorry, I meant to say changed "IAC" and not "Throttle controller".

 

Is this after being HARD on the brakes? It could be a vacuum leak in the brake booster.

 

It is not necessarily during hard break but it does happen when I slow down to a stop light and as soon as I stop the RPM comes down from 3k to dead engine. Also, sometimes, it is idling fine, when I'm parked then the RPM starts to go down below 500 and struggles to stay on, and it might recover or sometimes it dies.

 

Make sure the idle RPM is below 1000. There's a circuit in the ECU that cuts the injectors if the idle is above about 1000 when the brakes are stepped on. Toyota figured that the engine doesn't need to be running fast when braking. Just a waste of fuel. If the RPM is much above 1000 when the brakes are stepped on, the ECU cuts the injectors until the engine RPM drops below the preset limit, then allows them to function normally again. Could be that yours is reacting a little slowly, so the engine dies.

Another possibility is the idle speed adjust screw. The one on the TPS, off the left of the intake hose. The o-ring on it gets old and brittle, possibly falling apart, and a piece jams up the air passage. Or allows too much air in for the ECU to compensate for at idle. When the ECU is being told by the idle switch on the TPS that the ECU should only allow enough fuel for a certain air flow. If the o-ring on the idle speed adjust screw is bad, you may be getting too much air for the fuel flow.
Easy enough to check. Take off the cover screw over the speed adjust screw, then run the idle speed adjust screw all the way until it bottoms out, counting the turns carefully, so you can find a starting point when you get it back together. Then unscrew the speed adjust screw all the way, and examine the o-ring. If it's bad, they're very easy to find. Most auto parts stores, and even hardware stores, carry o-ring collections that have one that will fit. Put a very thin layer of Vaseline or silicone dielectric grease on the o-ring, then re-install the idle speed adjust screw. Preserves the rubber of the o-ring a lot longer, and allows a better seal. Run it all the way down, and back it out the number of turns you counted before. Then use it to set the correct idle RPM.
Use an external tachometer. Don't rely on a installed, Toyota, tach. They're not all that accurate.

While you're at it, set the timing once you have the idle set properly. Double check the idle RPM once the timing is set correctly.

Good luck!
Pat☺

 

Thanks Pat for detailed help, I shall try it and report back.

 

Idk if you have a dashpot on your engine, but on my '86 22re the dashpot controls the throttle position when you let off the fuel. It slows down how fast the throttle goes to idle on a manual to prevent flooding/overrich when the engine suddenly decelerates. If the adjustment is too loose this condition occurs.