77Impala
The Hauler
1989 GMC C1500 5.7 with 5 speed manual transmission.
Month ago got random stall like symptoms where the engine would sound like it quite running, Service Engine Soon light would come on. My OBD I and II code reader could not find any fault codes. Paper clip in the A/B pins of the ODL found code 32 and I replaced the MAP sensor. Ran good for a full week.
2 weeks ago the idle started going up and down with once in a while less than a second engine loosing power. Check for vacuum leaks and only found the EGR would not hold any vacuum. Replaced the EGR.
Idle going higher at or above 2K and now does not lower to normal at all. Replaced the IAC and the throttle body gasket. No change. Sprayed carb cleaner around the lower intake and no change in RPM. Checked vacuum again and getting 22 inches of vacuum measured on the Air Pump vacuum line.
Replaced TPS as well and no change.
Also the Shift lamp is not coming on for it usually tells me to up shift when I go 36 mph in 4th gear in town.
Disconnected the IAC and restarted the truck and not only did it run high idle but no Service Engine light either which I expected it to come on with no feed back from the IAC.
Currently I have the battery disconnected to see if there is a hang up on the EPROM or computer.
I am suspecting that the EPROM chip is defective? Am I looking in the correct area or have I missed something?
Month ago got random stall like symptoms where the engine would sound like it quite running, Service Engine Soon light would come on. My OBD I and II code reader could not find any fault codes. Paper clip in the A/B pins of the ODL found code 32 and I replaced the MAP sensor. Ran good for a full week.
2 weeks ago the idle started going up and down with once in a while less than a second engine loosing power. Check for vacuum leaks and only found the EGR would not hold any vacuum. Replaced the EGR.
Idle going higher at or above 2K and now does not lower to normal at all. Replaced the IAC and the throttle body gasket. No change. Sprayed carb cleaner around the lower intake and no change in RPM. Checked vacuum again and getting 22 inches of vacuum measured on the Air Pump vacuum line.
Replaced TPS as well and no change.
Also the Shift lamp is not coming on for it usually tells me to up shift when I go 36 mph in 4th gear in town.
Disconnected the IAC and restarted the truck and not only did it run high idle but no Service Engine light either which I expected it to come on with no feed back from the IAC.
Currently I have the battery disconnected to see if there is a hang up on the EPROM or computer.
I am suspecting that the EPROM chip is defective? Am I looking in the correct area or have I missed something?
Last edited:
