GMC Troubleshooting Questions? Ask a Mechanic for Answers
Unfortunately there is no simple answer to this question as it could be cause by any number of things. Do you have access to a scan tool capable of pulling codes or live data stream? If not then the best I can offer is to check for vacuum leaks. I just had one the other day where the previous tech had knocked a PCV connector loose while replacing the screen beneath the oil pressure sensor. Hope this helps. If not let me know what kind of diagnostic equipment you have access to and we can proceed.