Here is the skinny… this is a 1991 Chevy S10 Blazer with a 4.3 l TBI engine that has 202k glorious miles on it. It was a Wyoming vehicle that hates being in Michigan. Gas mileage has shrank nothing. But the problem is…it likes to stall out. Usually it is short trips less than a mile…no problem. When I take my daughter to school (17) miles it is another story. This gives the old girl time to warm up. We go 50mph for 15 minutes or so… then slow down to a stop for a grand Michigan U turn and clunk…it stalls not to restart till we do a Chinese fire drill and my 16Y.O. Daughter gets in and she starts the car! Now if I keep the throttle open with a little input from the gas pedal it doesn’t die. I have changed the plugs (wires and roter 30k), fuel pump, air cleaner, cleaned the throttle body pretty good, new fuel filter. No Codes. Have I lost my car MOJO and my daughter has the touch…or is this a sinister polt of the universe to get me back for leaving Wyoming? I don’t know what to do with this great old truck.
Two possibilities come to mind. One is an idle air control valve that is dirty or worn. You can try removing it and cleaning it to see if that helps, or replacing it if you don’t want to mess with cleaning it. Your IAC valve is mounted to the side of the throttle body on this vehicle. Another possibility is a MAP sensor on its way out. This will definitely cause stalling issues on a GM of this era. There is no cleaning that part, though, and it will need to be replaced if it’s faulty. It’s cheap, though, about $30.
The idle air control valve can be cleaned by spraying carburetor cleaner through the by-pass port on the throttle body which is at the 2:00 position when looking from the front. If the cleaner is sprayed in short blasts the engine engine will stumble, the valve will open to compensate allowing heavier and more prolonged blasts. In a few minutes the valve should be working correctly. If not, it may need replacement.
Map…manifold absolute Pressure. I have been reading threads all over the web…There has been talk about map readings detecting barometric pressure. This truck was a wyoming machine for nearly all of it’s life. The altitude there is over 5k ft. Here in MI it is about 600. I know automotive cpu’s “learn” Ever since I got to mi the gas milage has dropped. Could this be the map? or the computer being confused? Any way…the Iac has been changed and still the problem is there. Once more there are no flash codes that would call the MAP or EGR as reporting bad. Still stuck