Have a 1990 s10 2.5 4cylinder 4speed idles rough and boggs when you touch gas I have replaced the egr valve plugs wires distributor cap rotor coolant temp sensor and I cleaned the idle air control val

if you haven't recheck that your wires are on right. if this is an injected engine put an expensive bottle of fuel cleaner in.

I actually had to replace my EGR valve and the gasket. I clean the valve well and reused both. I don't think the gasket sealed well enough though. So I went ahead and got a new valve, gasket and changed them. It runs a lot smoother now.

Check the compression on each cylinder. Also check for proper valve operation. You may have a flat cam lobe or bad rocker arm on either the intake or exhaust side which will give the rough idle you are experiencing.

You've already eliminated the spark plug & wireset, distributor cap & rotor.
Sounds like your car needs a tune-up, specifically, the PCV (positive crankcase ventilation) valve, and/of the EGR (Exhaust Gas Recirculation) valve.

Components checked/replaced during a tune-up are:
air filter
motor oil
motor oil filter
breather filter
fuel filter(s)
fuel strainer
PCV valve
EGR valve
spark plugs
spark plug wires
ECM or distributor cap & rotor
cabin air filter
transmission oil filter
transmission oil
engine coolant
check all vacuum hoses and lines

Troubleshooting the no-start condition - from the 1990 Mitsu Mighty Max Repair Manual:

Priority Action Part Type -- Cause
1 Inspect Battery -- Battery Discharged or Faulty.
2 Inspect Battery Cable -- Corroded, Broken, Shorted or Poorly Connected Battery Cable.
3 Inspect Distributor Cap -- Distributor Cap Cracked or Burned.
3 Inspect Fuel Filter -- Clogged or Dirty Fuel Filter.
5 Inspect Ignition Coil -- Faulty Ignition Coil.
6 Inspect Wireset -- Worn, Damaged or Faulty Spark Plug Wire(s).
7 Inspect Spark Plug -- Incorrectly Gapped or Fouled Spark Plug(s).
8 Inspect Starter -- Starter Motor Faulty.
9 Inspect Fuel Pump -- Low Fuel Pressure.
10 Inspect Solenoid Switch -- Faulty Starter Solenoid Switch.
11 Inspect Fuel Pump Relay -- Faulty Fuel Pump Relay.
12 Inspect Fuel Injector Pressure Regulator -- Faulty Fuel Injector Pressure Regulator.
13 Inspect Ignition Switch -- Improperly Connected or Faulty Ignition Switch.
14 Inspect Starter Drive -- Faulty Starter Drive.
15 Inspect Fuel Injector -- Dirty or Worn Fuel Injectors.
16 Inspect Fuel Pump Strainer -- Clogged or Dirty Fuel Pump Strainerat.
17 Inspect Engine Control Computer -- Incorrect Operating Information Being Delivered and Sent From The EEC.
18 Inspect Fuel Tank -- Fuel Tank Empty.
19 Inspect Carburetor -- Carburetor Flooded or Faulty Choke.
20 Inspect Distributor -- Worn, Loose, or Incorrectly Installed Distributor.

Check all of your tune-up parts. (Distributor Cap, Distributor Rotor, Spark Plugs and Spark Plug Wires) Also perform a compression test if no problem is found with the tune-up parts. Check also for vacuum leaks and the Intake Air Control Valve (IAC) for the "won't idle" problem.

http://groups.yahoo.com/group/villagerquest/

clean MAF sensor heated wires with spray carb cleaner first

check for minor vacuum leak and map sensor,pcv,egr valve

You should have your TPS and EGR looked at as those cause rough idles...Other causes are bad idle air control valve, bad plugs, bad distributor cap & rotor, a bad wire, bad O2 sensor, etc...

Had a computer on my 1990 Cadillac Deville bad, after changing plugs, wires, cap, fuel injectors, egr valve, etc.

The computer was not firing an injector and i had a miss and rough running mostly at 35 mph on the roads. It bucked like a bull.in a rodeo.

if you have a vacuum gauge you can check egr to see if it holds vacuum if it don't replace