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Not sure exactly where to put this as it crosses from fuel to exhaust to ecm, so I guess I'll start here and hopefully it will be filed where it needs to go...
(sorry for the long post, but it's a long saga)
I recently put a throttle body spacer on my F-150 with 351w. The truck has a full exhaust (headers, performance cat, muffler, 3" tubing all the way) and a K&N cold air intake system. Shortly after putting on the spacer, I got a trouble code saying that the egr valve was bad, I replaced it and the code shifted to the egr sensor reading out of tolerance, so I replace that. I still get the egr sensor code and a random turning on of the check engine light. In talking to a local speed shop, they said that they have seen this problem before with the addition of the spacers, and that I should do a resistance reading the the sensor with out the spacer, and then do another reading with the sensor insalled and put an inline resistor in place to make up the high or low value. A second shop suggested that I take a washer, drill it out in incriments, and put it in the joint where the exhaust pipe and egr meet up as it is being caused by my free flowing exhaust and I need to either slow down or restrict the amount of air going to the sensor. Any thoughts on doing either of these or does anyone else have a better solution to fix this. I can't get my truck to pass inspection in Virginia with the check engine light coming on randomly.
I don't see how a throttle body spacer would have anything to do with how the position sensor works. If it were a DPFE sensor where it measured EGR flow, it would make more sense for it to not have enough flow with the freer flowing exhaust. However, the position sensor reading doesn't matter what the flow is through the valve, it just measures how far the valve is opened. It should still be opening the same amount even with all the modifications. Give it a try without the spacer and see if you still have the code. If you do, start looking at all the small hard plastic vacuum lines and see if you can find one that is broken.