Toyota Repair: Eratic Idle, vacuum leak, vacuum lines

Question
Hi Ted,

I have a 91 4Runner V6, manual tranny with about 155,000 miles on her. The block was replaced about 5 years ago, so the block only has about 80K on it. Recently, I had my knock sensor replaced, and since then my idle has been acting weird. I took it back to the shop twice and they advanced the timing a bit, and adjusted the idle screw to get her up to about 1200 rpm at idle. She usually idles at around 800 rpm. The problem is after I've been driving for a while and I come to a stop, the idle sounds like it's loping. Like I have a 3/4 cam installed. When I give it a little gas it smooths out. But, as soon I start driving again and take my foot of the throttle it starts loping again. I've been told it could be a vacuum leak, but I can't hear one.
What do you think ?

Thanks,
Gus

Answer
It sounds like the egr valve may be staying on possibly the vacuum lines were mixed up when the intake chamber was removed to replace the knock sensor.
Look just below the cold start injector there are three vacuum hoses connected to three steel lines, they are arranged in a triangular configuration, the vac hoses are numbered, make sure that the #6 line is connected to the right line, the #5 to the left and the #3 to the top, the #4 vac line is connected to the airbypass valve.