Check the weld and that gasket, one of them could be leaking!

 

Okay, so I checked the bolts on the flex pipe, they're pretty tight already, can't get a torque wrench down there to torque them but I can't budge them. The gasket on it is brand new, just put it in when I put on the head. The exhaust manifold and intake manifolds are torqued to spec. I replaced the EVAP purge valve since it was cheap, did nothing. I checked the fuel pressure, getting 55 psi so that's okay. Took out the air filter in case that was causing the issue, did nothing as well. I don't see anywhere where there could be a vacuum leak, checked just about every vacuum line. When it starts up, it starts at 1000 rpms but then drops to 650 and idles around there after like 15-30 sec. Any ideas what it could be?

 

Flex pipe

 

Can a flex pipe go bad that quickly? I had it replaced in January 2019.

 

If the upper engine mount is shot, yes, if the weld at the repair is porous, yes. Can you maybe take a picture of the joint?

 

Okay, here are the pictures of the flex pipe. Sorry, couldn’t really get any really close pictures of it. I tried testing for a leak with a rag in the tail pipe and I didn’t see any smoke coming from the flex pipe.

 

Ok, next remove the exhaust manifold heat shield, inspect for a cracked manifold.

 

Okay, got to check the manifold today, no cracks in the exhaust manifold.

 

Question out of left field... Have you done a compression or leak down test since you rebuilt the engine?

 

No, I haven't done a leak down or compression test. I bought a leak down test kit a few months ago but it didn't have the right adapter, never thought of getting the right adapter, do you recommend doing one? I just assumed that it most likely isn't associated with an engine issue since it's only when it idles at temp. MPG dropped to 16mpg due to the rich conditions with a lot of short-distance drives. The oil level has stayed the same since replacing the head and timing chain.