A few things I'd suggest:
1. Check the fuel pressure at the rail.
2. I assume that you have a scanner that reads individual cylinder misfires -- is #4 the only one showing anything significant?
3. Just to rule it out, do a quick CASE relearn. If the crank position sensor has been changed this might make a difference, and it's quick and easy.
4. What is the MAF reading in g/sec at hot idle? It should be close to the engine displacement in liters.
5. Look at the short- and long-term fuel trims. You could have an injector that's over- or under-fueling. Might do an injector balance test.
1. Check the fuel pressure at the rail.
2. I assume that you have a scanner that reads individual cylinder misfires -- is #4 the only one showing anything significant?
3. Just to rule it out, do a quick CASE relearn. If the crank position sensor has been changed this might make a difference, and it's quick and easy.
4. What is the MAF reading in g/sec at hot idle? It should be close to the engine displacement in liters.
5. Look at the short- and long-term fuel trims. You could have an injector that's over- or under-fueling. Might do an injector balance test.
