Cadillac ELR Rough Idle Points to Air Intake Issues

Having some experience working on hybrids, I faced nearly identical symptoms with my 2013 Cadillac CT6 hybrid last year. The rough idle and engine stalling issues turned out to be related to a faulty vacuum hose connection between the pump and valve. After noticing similar check engine light and idle problems, I took it to a specialized hybrid workshop. The diagnostic revealed that the air intake system was not maintaining proper pressure due to a deteriorated hose connection. The symptoms got worse especially when the engine was warm, which matches your description. The repair involved replacing the defective hose assembly and checking all related air supply components. Total cost was 175€, including diagnostic and parts. The idle issues disappeared completely after the fix. For a more accurate comparison, could you share: Current mileage on your ELR, Whether the idle problems occur more frequently in specific conditions, If there are any unusual sounds from the engine bay, The specific error codes from the check engine light This information would help determine if your vacuum hoses and air intake system are experiencing similar issues to what I encountered.

Thanks for the helpful insight about the vacuum hose connection. Last service was done at 142000 KM and the manifold pressure issues started showing up shortly after. The air valve problem seems to get worse particularly during cold starts, making the idle problems more noticeable. The check engine diagnostic shows P0507 code, which further points to air supply irregularities. Will check the connections around the air intake system before booking a shop visit.

Thanks for providing those additional details about the timing and the P0507 code. This aligns perfectly with my CT6 hybrid experience, my idle control issues also started showing up right after crossing the 140000 KM mark. The P0507 code specifically relates to idle control system RPM higher than expected, which matches with the air supply irregularities we both experienced. In my case, the throttle body also needed cleaning along with the vacuum hose replacement to fully resolve the idle problems. During cold starts, a compromised air intake system can definitely cause those symptoms, as the engine management system struggles to regulate the proper air-fuel mixture. Before I got mine fixed, the cold start issues became increasingly frequent. For reference, when my mechanic did the full repair they: 1. Replaced the vacuum lines 2. Cleaned the throttle body 3. Checked for additional vacuum leaks 4. Verified proper manifold pressure The total cost including the throttle body service came to 290€. The check engine light cleared and the idle problems disappeared completely after addressing both the vacuum system and throttle body.

My 2015 ELR has indeed been showing these exact symptoms. The manifold pressure issues and idle problems during cold starts match perfectly with the vacuum hose diagnosis you suggested. The P0507 code and air supply irregularities definitely point toward the air intake system being the culprit. After hearing about your similar experience with vacuum lines and throttle body cleaning, I feel much more confident about the repair direction. A 290€ repair bill sounds reasonable compared to my initial concerns about more serious engine problems. Will have my local shop check the vacuum connections and clean the throttle body first, since these seem like the most likely causes of the engine stalling and rough idle conditions. Its helpful knowing the complete fix might need all four steps you listed to properly restore normal manifold pressure readings. Thanks for breaking down the actual repair experience, this gives me a clear path forward instead of potentially wasting time and money exploring other issues.