99 Camry "check engine" light that won't go out

I own a 99 Camry LE, 2.2 L engine with approximately 116k miles. In early June, my check engine light came on and I took it to a
mechanic(one man operation) I had been using for approx six months based on a referral. He had replaced the timing belt/water pump in February, did a good job, and charged a reasonable price. So, I took my Camry to him for the "check engine" light, was charged $184.96($96.79 for the part, $81.64 for the labor) to replace a defective Vacuum Switch Valve. I drove twenty minutes down the road and the "check engine" light came on again. Took the car back for the second time and he said the problem was two hoses he had crossed mistakenly(no charge). Drove the car twenty minutes down the road and the "check engine" light came on again. Took it to the mechanic a third time and paid $123.99($77.45 part, $41.31 labor) to diagnose and replace a Vacuum Valve. I asked him the obvious question, that is, did the first part really need to be replaced? He said it was part of a process, whatever that meant and I agree, part of process that's going to put me in the poor house and cause me to pull the last few hairs I have on my balding head. Got in the car, got twenty minutes down the road, the "check engine" light has come on for the "fourth" time. I've left a message on his answering machine to notify him we needed to talk about this thing. So, here I am, $300 plus poorer, with a "check engine" light that won't go out and a mechanic who has made three failed attempts to repair the problem. What is the likelihood that the parts he replaced actually needed replacement? And do I take another chance with this mechanic and throw more money into the black hole? Any words of wisdom?
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Are you dealing with the evaporative emissions system or the EGR system? Which codes do you have? It sounds like the guy you're taking your car to is definitely a mechanic and not a technician. There is a big difference between replacing timing belts and diagnosing OBDII engine control systems correctly. Anyway, give us an idea here of what you're working with. What codes keep reappearing and which valves have you replaced thus far?
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Had a similar problem with my 98 Avalon. At my mechanic's suggestion, I disconnected the negative battery terminal for 20 minutes, and the check engine light finally stayed out. That was over a month ago and it's holding. He had "reset" the light several times with two different plug-in diagnostic gizmos but it kept lighting up again.
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took your advice...disconnect neg battery terminal and thought I was home free. Drove almost 250 miles and the light came on again. Gonna get the codes or take to dealer at this point
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<snipped>

Why don't you get the codes and post them here?
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Ray O
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As qslim suggests, find out exactly which trouble codes are coming up on the scan tool, and if it is the same codes. If it is the same codes, I'd bet that the person working on your car is not checking the function of the parts before replacing them. In almost every case, the factory repair manual has a procedure for checking part function before replacing it. I would find a competent automotive technician to diagnose and repair the condition, or post the codes here and qslim or I can try to give you some hints. If the trouble code is P0440, check to make sure your gas cap is tightened until you hear it clicking.
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