1990 Volvo 240 Sedan GL, 140,800 miles I started hearing a funny sound (like a card in a bike tire flapping) from the front right of the car. The sound is easier to hear when accelerating in second and third gear. A week later the check engine light came on. A 2-3-2 code was found indicating the engine was running either too lean or rich at idle. A check for an exhaust leak found a small leak at the rear gasket where the exhaust manifold attaches to the engine. The suggestion was to replace these gaskets. My mechanic noted the manifold might be slightly warped so it would need to be machined. While this leak may be the cause of the new sound I am hearing, the leak has been their for *at least* 11 months and 5,000 miles. It does not appear to be any bigger than before. Also a review of the original owner’s maintenance receipts shows no indication that the oxygen sensor was ever changed. Right now the two symptoms (new sound and check engine light) are being treated as connected, but maybe they are not. What is the best way to proceed? 1) Replace the leaking gaskets, including machine the manifold (~4 hours labor, plus parts and machining cost), and see if this resolves both the sound and engine light, or 2) First replace the oxygen sensor to see if this resolves the check engine light, and then deal with the new sound (which I doubt would be related to the oxygen sensor – correct?) Thanks.

 

Replacing the O2 sensor is less expensive & involved than the manifold effort & the former is on a more certain problem-solving track.

 

I would take the money the mechanic wants and install a new exh manifold myself.