Finding reason for P400 is driving me crazy

[urdrwho]

Well after much cleaning I fianally got the carbon out of the tube that the goes to the bottom of the back pressure transducer. To my surprise it is blowing air out and I expected manifold vac.

 

Anyhow I thought it would finally get rid of my P400 code. Went for a long drive, high speed low speed uphill and down, then on the 40 MPH straight road, bam....threw a code. It is always almost the same exact speed and RPM.

 

The BPT tests well, the EGR valve holds vac and has been cleaned of carbon and the needle moves fine. Changed out the vac lines. Cleaned out the throttle body, well let me say cleaned as best as I could with it on the car.

 

Still have to install the new EGR gasket that is laying in the glove box. Then the next thing will be to get the propane tank and search for vac leaks. No vac leaks off comes the throttle body for a good cleaning. Or do I want to do that first.

 

Although to me it still points to clogged ports because pushing up on the EGR does not do a darn thing to the idle, not even a blip. But where is the clog?

 

Darn car runs well, gas mileage is ok and I am tempted to just say the heck with it. But that isn't me. Even though it is my son's car I try to keep any car in my driveway running as it should run.

 

Hm? I still haven't tested the solenoid and that is mainly because of its location.