Mitsubishi Repair: rough and steady idle, o2 sensors, mitsubishi eclipse

Question
Good day. One month ago I purchased a 1996 Mitsubishi eclipse rs with 130,000. I have given it a tune up, replaced the rear seal, and have had it checked at various mechanics. It will idle low, rough and steady, almost like its throbbing. But the car will run fine when in motion. The car also runs fine in idle when the A/C is engaged. Here is a list of things I ve done to the car:
replaced rear seal
changed oil/oil filter
replaced air filter
replaced fuel filter
replaced spark plugs
replaced spark plug wires
replaced catalytic convertor
replaced muffler
replaced all belts (minus the timing belt)
replaced all hoses
replaced EGR valve
cleaned EGR piping
cleaned throttle body
added engine cleaner
added fuel line/injector cleaner
ran compression tests/no problems

Whats left to do....
change battery/low, but not enough to show serious signs of electrical failure
replace o2 sensors/see below

lights, brakes,..other things not related to the engine.
I have had it electronically scanned at 3 shops.
The first shop said the scan showed it needed a new EGR valve and o2 sensors.
They also recommended that my valves be replaced.
The second shop said the scan showed it needed a new EGR valve, and catalytic convertor
I replaced the EGR valve and catalytic convertor
Same symptoms
The third shop showed the map sensor voltage reading was high and that there was EGR errors.
Before I shell out money on what might be more unnecessary repairs, what could possibly be causing this rough steady throbbing idle???
Louis

Answer
Louis: Your car is the right year for bad computers, Mitsubishi farmed out the building of their computers to another company and that company did not build very good ones. A piece will start to leak into the computer and with time it will kill off the computer. One way it shows up is with a rough steady throbbing idle. I would get the computer checked, or maybe even replace it. I know, just what you need is another costly idea. I understand that. But if you step back and look at all you have replaced, you have done a lot of that car and it should run too. My guess would be bad computer or weak sensors. Your car is only as good as the computer, it controls everything. Ok, my manual has this to say, a vacuum leak, air filter clogged, fuel pump not delivering sufficient fuel, a leaking head gasket(but the car is not blowing white smoke out of the exhaust is it, heating or using water, so I would say it is not that), how old is the timing belt? Was it replaced at 60,000 miles? If not I would think about doing that, I would do the timing belt before the valves. I mean the valves, oh holy cow don't do that one yet. I don't think that would mess that much with the idle anyway. Sounds like the shop thought they would make an easy buck on you. But listen get yourself a repair manual on your car, most parts stores have them for around $20.00 and read up on your car. You can have the fuel pump checked to make sure it is putting out enough fuel. The manual would explain what you should be looking for on that. By having your own manual, the shops would not have one up on you. In that you need new valves. If you are still getting errors, it sounds like the computer to me. But still try testing the fuel pump, check for a vacuum leak well do the cheaper things first. If still a rough steaky throbbing idle I would have that computer checked. Sometimes you can smell the burnt computer as you open up the area where the computer is at, sometimes not. I do hope this helps you and keep an eye on those shops some are just out to make money off you. When you really don't need the work. God bless: Linda