Buick Rainier Vacuum Leak Killing MPG, CEL Flashing

Had a similar issue with my 2004 Buick LeSabre. The hissing sound combined with poor fuel economy pointed to an intake manifold leak. The check engine light triggered due to the system detecting unmetered air entering the engine. A leaking intake hose creates a vacuum leak that throws off the air-fuel mixture. The leak detection test confirmed multiple small cracks in the rubber intake hose between the throttle body and air filter housing. These cracks developed over time due to heat exposure and normal aging of the rubber. The repair required replacing the intake hose assembly and cleaning the throttle body while it was accessible. After the fix, fuel economy returned to normal and the check engine light cleared. This was a relatively straightforward repair but leaving it unfixed can lead to more serious engine performance issues and potential damage to the turbocharger if your model has one. Would strongly suggest getting it checked soon, as running with incorrect air-fuel ratios can cause additional problems over time.

Thanks for sharing your experience with the LeSabre. My Rainier has been running much better since the repair. The engine misfire symptoms completely disappeared after they replaced the cracked air intake hose and installed a new air filter. The fuel economy is back to normal too. Wondering what you ended up paying for your repair? Also, have you noticed any other issues pop up since getting it fixed? Just want to keep an eye out for potential related problems.

Found your question about repair costs interesting. For my LeSabre, the total bill came to 100€ for fixing the leaky intake hose, which seems reasonable given the detailed inspection needed to locate the exact source of the vacuum leak. Really glad to hear your Rainier is running better after the air intake system repair. Getting that cracked intake hose replaced was definitely the right call. These leaks often start small but can cause bigger problems if left unchecked. Since the repair, my car has been running smoothly for months with no related issues. The fuel economy stayed consistent and the engine maintains steady performance. Just make sure to have your air filter checked regularly during maintenance, as a clogged filter can sometimes create similar symptoms. One tip: pay attention to any changes in engine sound during acceleration. A new hissing noise could indicate another vacuum hose starting to fail, though its pretty rare for this to happen again if quality parts were used in the repair.

Took my Rainier to a different mechanic this time and really happy with how it turned out. The intake manifold diagnosis was spot on, they found multiple cracks in the vacuum hose right where it connects to the throttle body. The engine misfire turned out to be directly related to this issue. Total repair cost was 250€ including parts and labor. They also noticed my air filter was pretty dirty and replaced that while they were in there. The whole job took about 2 hours. Been about 3 weeks since the fix and the fuel economy is back to normal. No more hissing sound and the check engine light has stayed off. Engine runs much smoother during acceleration now. Really appreciate the advice about getting it checked quickly, definitely saved me from bigger problems down the road.