2000 cavalier idle problem

Hi, hope someone out there can give me a hand. I'm fixing a Cavalier 2.2l for a friend, and he says it was running fine until the idle started jumping from a little high to around 1000 rpm above normal. I figured it was the idle control valve or map sensor or maybe even the oxygen sensor or the tps. NOPE.... so i replaced the fuel pump (filter is only around 6 months old) still the same thing. the only codes it was spitting were high idle problem and egr..... thought it could be a vacuum problem, so pulled and cleaned the throttle body and tried covering the vacuum ports on the tb no change. Can anyone PLEASE give me some advice about this POS? Thanks.

Do you have a scan tool? What are the IAC counts? Did you replace the IAC? Do you have an IAC tool?

I did replace the IAC, i only have a little code reader, so i can't get any counts. one strange thing that it's doing is the idle evens out (high) when you put it in gear, but when you give it some throttle in neutral it starts surging at higher rpm's. I also got a check gauges light on for a little bit, but it went out again. This thing is got me stumped, but i really appreciate the help.

OK, now i replaced the intake manifold gasket and air charge temp sensor, and even the o rings on the injectors.... still the same s***. Can the evap purge cause such a problem? or am i looking for a computer next? It seems to be running too well for a timing chain or belt problem but this thing is becoming a huge pain in the ass. Can anyone out there PLEASE give me some help? Thanks again, Chris.

This is where a scan tool is valuable....if Idle is high and IAC counts are high, the computer is making this happen,, for some reason(need to look at data...tps, MAP, ECT, etc.).....

If idle is high, and counts are low or zero, this is usually a vac leak.....

Thanks for the help so far. Replaced the timing chain on this p.o.s. bought a vacuum tester and it pointed at a misfire or valve problem. Replaced the plugs and wires and got a better diagnostic scanner which, showed everything ok except for the jumping idle, and when i cleared all codes, it jumped the idle back up to way too high. Sooo, i pulled the head and the gasket looked passable but two of the exhaust valves had some crap above them and the guides and seals are a bit loose. I plan on replacing the seals and all of the gaskets and cleaning the valves and surfaces, but my question is, can anyone recommend anything else i should do or look for before i reassemble this motor? The only sensor not recently replaced is the cam sensor, and the guide info says that it will cause the motor to run too rich, which i guess, would cause the brain box to compensate but i'm sick of throwing parts at this thing. Guess i could buy another 2000 cav to stick all of the new parts on...... but i don't think so. This better not be a case of 2 bad IAC"s or someone at Advance will be sporting a IAC suppository. Again, any help is much appreciated.