I have asked this question before, but now I have ALOT more information to try to help me troubleshoot this problem.

First off, My Egr Throttle Valve diaphram vacum line has to be disconnected for my truck to run smoothly after it warms up, WHY?

If I let the truck idle cold all is well, but after driving the truck and it is warmed up, then you come back to an idle, after about 20 secs of idling the check engine light will come on. The code is P0404, for EGR perf/Ckt. If I raise the RPM's just 100 rpm's at idle, the check engine light will not come on.

I have removed the EGR valve and cleaned and inspected it and reinstalled it, all is working properly, and the diaphram is not ruptured. I then hooked the EGR Throttle valve diaphram vacum line back up and the truck idles fine cold, and runs fine down the road UNTIL the truck is warm and a vacum is on the EGR Throttle valve diaphram, when you come to a stop and the rpm's fall below about 1200, the trucks runs like crap and chugs and pings until I unplug the EGR Throttle valve diaphram vacum line then the actuator springs to the unvacum position (open or closed?) and the truck idles fine and smooth.

So come on Diesel techs out there, help me out! I am just a Airplane mechanic, and trying to learn this beast. I still get 20 MPG and trucks runs great, I just have to remember to elevate the idle 100 rpm's at stoplights so the CEL will not come on.

Right now I have the EGR Throttle valve diaphram vacum line disconnected and capped, all else is as it should be, this has been this way since I purchased the truck nearly 5 months ago, and I cannot figure this out.

Come on diesel gods please help!

Sorry it is so long, but I wanted to try to explain in as much detail as possible.

Thanks,
John

Have you tried a new egr ?

I did not think our LB7s had an EGR.

Probably wrong but I thought the LLY was the first to use an EGR.

I would like to know the same thing. My CEL come on intermittantly with the same code. I thought it was a sticking valve, due to soot. it seems to clear when I drive easy, but as soon as I get on it and blow a little smoke it throws a code. I would like to completely remove it, but I do not know if you can do this.

Here is a list of components that could set that SES. This list is from a '04 LB7. You should get a service manual for your truck to insure that yours is the same. The service manual will give you all the steps for testing each component.

Leaking vacuum lines.
Bad vacuum pump.
Bad EGR valve control solenoid.
Bad EGR throttle valve control solenoid.
Bad EGR valve vacuum sensor.
Bad EGR valve vacuum vent sensor.
Bad EGR valve vacuum diaphragm.
Bad EGR throttle valve vacuum diaphragm.

chugging and rough running would be from egr feeding during idle, test those components WanaDmaxsub listed. might try blocker plate in egr line and see what it does then. your truck must be CALI or N.E. truck with egr. look at door or underhood emissions sticker.

your truck must be CALI or N.E. truck with egr. look at door or underhood emissions sticker.

This is what I was thinking. Might be trying to troubleshoot something you do not have.

I DO HAVE A EGR VALVE, I removed it and checked it all out, if the EGR is the problem, then it is beyond me, but the EGR valve is 160 bucks for a guess, and I do not believe in throwing parts at something for troubleshooting. I guess I am going to be getting a service manuak for Christmas.

Thanks for the direction WannaDmxsub, I know you have chimed in before on this issue.

Oh yea, I have been out of town for a family emergency so that is the delay in answering............

Hope everyone's OK.
The cost of the manuals may seem expensive at first but it's well worth the cost when you need to find/test/figure-out something.