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[Kep]

When you do the work yourself it is almost always worthwhile to test the parts before replacing them. A lot of times we can clean a part and it will be fine. However, when you start paying a mechanic it is often just cheaper to replace a part than test it, let alone clean it. In those cases it is a guessing game but cheaper to guess than be wrong. On more expensive parts and systems it becomes feasible to test and/or clean.

If you want to try doing some of this yourself you could easily check the resistance of the wires with a $10 multi-meter (though if you get a digital one for more $$ you will be able to use it on other things as well). 20,000 ohms or more indicates that the wire needs to be replaced. I get the cheap lifetime guarantee wires and change them out about once a year. Do you have a distributor on this model?

Your points on the EGR System and the Engine Coolant Temperature sensor are both likely culprits. If you can reach it there is a simple test of the EGR by merely pressing up on the diaphram and bogging the engine down. Not a test of the system but a decent test of the EGR valve itself. You can test the ECT sensor with a multi-meter by monitoring the resistance as the engine warms up. As the engine warms up the resistance should lower smoothly. If the resistance fluctuates the ECT is failing and will need to be replaces.

If you plan to do this yourself, I would encourage you to clean the EGR system, throttle body and the IAC valve. Clean out the PCV valve as well. Get yourself a digital multi-meterm, some metric sockets and wrenches and a torque wrench. Get one or more shop manuals (I like the Chilton's). When the manual doesn't make sense do a search here for extensive reports or post up and someone will likely help you figure it out.

Luck,
Kep