My son's Civic is losing power while at highway speed. Not necessarily under load, but just at cruising speed. The engine just bogs down and downshifting does not help. If I put it in neutral and take my foot off the gas momentarily, I can put it back in gear and it's fine.

Some background on work we've done this summer. New clutch, radiator, fuel filter (needs air filter). After the clutch was done, we got a CEL indicating a slow response from one of the O2 sensors. Replaced both with Bosch, which within a new miles gave another CEL (P0133, slow response primary O2 sensor). Replaced the primary with an OEM sensor and so far, it's good (knock on wood). (Will RMA the Boach back to Amazon.)

The power loss happened both with the Bosch and the new OEM sensor, so I don't think that's the problem. Sure would appreciate any input.

 

Does the CEL turn ON when the problem occurs? If so, retrieve the trouble code.

Otherwise, you might want to measure the fuel pressure, clean the throttle body, and check both the throttle position sensor and the catalytic converter.

 

sounds like your cat converter could be clogged up from debris

 

I agree with above...I just had the exact problem on the highway and after i did a full tune up I found out it was my muffler. It was rusted inside and broke. So I would say make sure that there is no obstruction in your whole exhaust system, and dont think that because when u hit the gas air comes out that its fine :P