If the EGR valve is not sealing properly, the exhaust gas will dilute the incoming air which will make the engine idle too slowly and rough, however, the Engine Computer will raise idle speed back to specs. The way to see if that is taking place is to use a scanner to view the "idle steps". The computer places the automatic idle speed motor to one of 256 positions, or "steps". As the motor's shaft slowly rotates, it turns a threaded shaft that retracts or extends a pintle valve. That valve opens an air passage around the throttle blade. At the same time, it increases the amount of time it pulses the injectors open to provide more fuel to go with that extra air.
If you find the AIS step is "0", minimum throttle needs to be relearned. Under normal conditions you'll find it to be around step 32. With a single-cylinder misfire on a V-6 or V-8 engine, it will be somewhere around step 50. If you find the step number is quite high but idle speed is too low, either the AIS motor is stuck or the air passage is blocked with carbon. That carbon used to be a common cause of low idle speed in the late '80s and early '90s on some engines, but with the better fuel additives we have today, that problem is rarely seen now.
You can also use the scanner to raise idle speed to 2000 rpm in 200 rpm increments. That tests the AIS motor and wiring, and proves the computer has control of it. On some models, this test will not respond if minimum throttle hasn't been learned yet. Also, this test doesn't change idle speed that is programmed into the computer. Once the test is stopped, idle speed goes back to specs.
The fuel pump should not be related to this problem. The pickup sock sits in a small bowl in the middle of the tank. That prevents gas from running away from the pickup when you go around corners. The bowl is kept full by the very high volume of gas that gets pumped to the engine, then returns through the pressure regulator and the fuel return hose. If there is something wrong inside the tank, you will observe different symptoms depending on how much gas is in the tank.
You might consider checking the fuel pressure, but it has to be pretty low to cause running problems. Specs for your engine is 47 - 50 psi.
Wednesday, February 13th, 2019 AT 3:34 PM