OK Guys, I've got a weird one. I'm dealing with a high mileage 04 with a blocker plate and no cat. I'm getting a rough idle in park, with a slight surge sometimes that shows up on the tach.

When I check the balance rates in park they are all .89 . All of them. When I drop it in gear they all look like they should -2 to +4 and in between.

Any ideas??

if you have a tech 2 you can plot out the Fuel pressure regulator. I'm not sure what other scantools will allow you to plot it out on a graph. If you can somehow, you will be comparing actual and desired, actual should be a straight line with desired. If there is a "sawtoothed" pattern for actual then it is bad (fuel pressure regulator).\

When was the fuel filter done last?

I have the Kennedy gauge and the fuel filter checks fine. I only have the Predator for diagnostics.

i'm assuming no codes..... the .89 is odd...... were these balance rates obtained warm or cold (engine temp)?

i'm going with a bad fuel pressure regulator or poor fuel quality. I wish i could help you more but it's tough without a tech 2 as thats what i'm used to using.... i have full access to Service information so if you need anything just send me a PM or hit me up on AIm - B000STED (zeros)

The only codes are the normal ones for the egr blocked. The readings were warm.

It almost seems like the computer is going into a default idle mode. The Predator can moniter commanded vs. actual fuel pressure. I'll check that this weekend.

I have the Kennedy gauge and the fuel filter checks fine. I only have the Predator for diagnostics.

While the Predator is a nice scan tool, I definitely prefer the Tech 2 for it's sampling rate.

I would try a heavy dose of lubricity additive and see what happens.

Two bottles of Stanadyne so far. This morning, cold, the balance rates looked normal. I'll check them again later today. Fuel rates also look normal.