Crossposted from turbobricks.
So, I've been dealing with a couple of issues of late. Initially the car's idle would fluctuate/lope at red lights, ie foot on the brake trans in D. Shortly therafter the ck engine light came on and I retreived a 113 and 121 code.

So I cleaned the AMM and replaced the O2 with a genuine Bosch from FCP. The check engine codes were cleared and have not reappeared after a weeks worth of commuting 20 miles a day. However, It still has this loping idle. I have installed new plugs, cap, rotor and air filter. I have also cleaned the flame trap and replaced the vacuum line to it as well as the vacuum line to the Fuel Pressure Regulator.

I did disconnect and plug the vacuum to the booster and the situation went away. BTW the valve on the line to the booster seems to operating okay, only one way airflow. I will say though that I have traced an ugly reedy sounding squeak to this valve, like someone hitting a bad note on a clarinet.

So the questions are:
Am I on the right track?
Is this common?
And just how freaking expensive is a booster going to be?
Is there anything else I could do to verify this?
http://i266.photobucket.com/albums/ii264/SpineyNorman245/010108010207010412200706282e6d7be3f.jpg
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94 940 Red, 93 240 Wagon