IAT Circuit malfunction
I had to replace my EGR valve because it was stuck, I took the opportunity to check all of the vacuum lines and replace one. After replacing the EGR and the downstream O2 sensor the truck ran better, and worse. It would not buck and heave like before but it was acting like there was a vacuum leak somewhere. It would idle fine, then stumble and run rough, then idle fine again. It would also do this through the rpm range sometimes.
I just ran a diagnostic which told me the IAT circuit was not working. My book has nothing about IAT and I was about to post on here to find out if that was the intake air temp sensor. There was a second code telling me the system was running too lean but that may be related to the IAT circuit. Thanks guys!
edit: The mass airflow sensor was cleaned earlier this spring but I'll double check it again. It was contaminated with filter oil from my K&N filter, one of the reasons why I switched to the Secret Weapon intake. The filter does not need to be oiled and filters better than the old K&N.
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