I have spent quite some time doing research on this issue. I cannot seem to find a straight answer (or idea).

363,000 miles 3VZE in an 89 4Runner. For the last year it has had an idle problem as follows:

Idles perfectly @ 850rpm when started (once warmed up of course).
50% of the time (flip of a coin) the truck either idles at 850 perfectly when pulling it out of gear (standard trans) and coming to a stop (think red light, stop sign). Or, it will bounce from 350-500 and obviously act like it is about to stall every time it bobs back and forth from 350 to 500. If I wait 15 seconds (at the light of stop sign) the idle goes right back up to 850. The bobbing idle from 350 to 500 is almost like a major vacuum leak, as how the engine would act if I tried to idle it with the oil cap off the valve cover.

Those 15 seconds risk stalling, and I am sure the problem won't get better as time goes on.

Things I have done:

Plugs, Denso (FSM PN) gapped at 31. Truck is good and responsive.
A good throttle body cleaning.
Checked for vacuum leaks with starting fluid and cannot find any.
Valve cover gaskets and rear cam plugs (had a leak on driver's side valve cover, it is now fixed)

I am stumped, especially because the issue is intermittent. Anyone have a hunch about something? It is probably vacuum related, but what would cause the delayed vacuum issue when coming out of gear and stopping?

 

Thought about deleting this thread because I worked within another thread to solve the problem. I will keep it alive for search function purposes.

Idle issue has been resolved.

I replaced all the vacuum hoses related to the EGR vacuum modulator (even though they seemed okay, a bit rotted on the surface)
I used carb cleaner to clean the EGR VM's filter, and inside the housing.
I used carb cleaner through all the vacuum line hard lines.
I used carb cleaner to clean the EGR valve through its vacuum ports without removing the EGR valve.
Finally I found that the vacuum line from the BVSV to the throttle body was disconnected. I inspected and reconnected the line (knock myself on the head with that one).

Idles smooth and steady at 850rpm.

For me, it was old age maintenance, so I suggest those who have this problem start with some cleaning before throwing parts at it. Engine has 363,000 miles on it.

 

i have the same issue... going to check this now...

 

Good to hear. I suspect a lot of "vacuum leaks" are actually carbon in EGR system problems. That mileage is encouraging. Any oil leaks at main seal? As an aside, I assume I'll be posting a few comments in near future on Flamethrower injectors. 3 days in and I highly recommend them. Like a tune up on steroids IMO.

 

It is currently 100% leak free believe it or not. I replaced the rear main seal at 321,000 or so. Interesting about the injectors.