Got my 1991 z28 5.0 tpi, last week drove it home and noticed when i let off the gas to slow down the rpm would go to below 500 rpm so i hit the gas then would go up to normal rpm's of the speed i was going. Changed all spark plugs, rotor, dis cap, fuel filter, and cleaned the fuel pressure regulator, also changed the o2 sensor because SES light threw a code 45, any ways to make a long story short the car still wants to die on me after i let off the gas driving down the road, SES comes on still for code 45 and when driving at 40mph the car feels like it misses. This only starts when the car has been running for 5 min or so, also there is a hesitation when i first start out like at a light it goes then no power then it takes off (like i pushed the gas then let off the gas then pushed the gas again but never let go of gas). Anyone have any clue what i need to try next.

 

Check your O2 sensor ground. Its a small tan wire at the right rear of the engine. Its probably broken loose from the engine. Reconnect it. test O2 voltage at the sensor connector it should toggle from .200 to .800. If it sticks high, try disconnecting the sensor and measure at the harness side. If it still sticks high, recheck the ground circuit.