1990 4Runner 3VZE rough idle, about 500 rpm. Stalls a lot. I cleaned the throttle body, replaced a few vacuum hoses, and went looking for other vacuum leaks. I hear the sucking sound on the left side of the engine from around the intake plenum and I'm thinking it might be a leaking intake manifold gasket.

This all started when the car backfired last week while starting up. Since then, it has run like total crap.

I'm not losing antifreeze. Is it possible to have a vacuum leak in the manifold gasket without a corresponding water leak? Is there something else under the plenum that I should be looking at? Is there a way I can test this to be certain it is the manifold gasket before I got to the trouble of replacing it?

I'm considering dynamite if I can't get this fixed.

 

Well If you use dynamite, you wont have to worry about vacuum leaks. Pretty loud and real messy. Before you set it off you might check the intake air hose from the filter box to the intake. Since you said it backfired it may have cracked the hose. If you can hear a vacuum leak but cant fine it, get someone else to look at it. Sometimes we look for something so hard we cant see it..

 

I think you can use carb cleaner to find vacuum leaks on your rig like others can on a carbed truck? Just spray it gently around the manifold to see if changes the idle. Then it's probably leaking

 

In addition to carb cleaner, I have tried unlit propane gas as well (or any other butane torch of sorts).

 

I have some carb cleaner and a propane torch. I'll try those out, but probably not at the same time.

ThanX

 

If those don't work, you could find a shop that can smoke test it, or dynamite.

 

It would seem I have no business under the hood at all. After failing to find anything with the carb cleaner, with the propane, and with another person looking at it, I was having my father-in-law (an old gearhead) listen to it, but he couldn't hear anything that he thought was a vacuum leak and my wife, just out of the blue, said, "check the timing." So I scoffed under my breath and did it to exclude it from consideration. So this thing was waaaaaay out of time. The mark was all the way at the bottom of the gauge, nowhere near the "10" that it should be. It hasn't run this good in a long time. I just got used to it being underpowered, so I guess I never thought it wasn't supposed to be driving like that.

Anyway, thanX for the ideas. For now, the dynamite will have to wait.

 

Yeah you owe the lady a really nice dinner

 

Shucks, I already had my fingers in my ears.

 

what you need to ask is why did the timing jump when it was backfiring. THAT is not normal.

 

Could that be a cam migrating? I've heard of that happening on 22Rs.