Car does not rev?

KDINERO

MEMBER
2004 SUBARU IMPREZA
1.5L
4 CYL
2WD
AUTOMATIC
120,000 MILES

2004 subaru impreza wagon developed a problem where it will not rev. It will start and idle but will not rev past idle. I changed the fuel pump, O2 sensor, removed the exhaust manifold and it still will not rev. What could be the cause of this? There were no trouble codes either.

Friday, September 5th, 2025 AT 9:57 PM

3 Replies

KEN L

MASTER CERTIFIED MECHANIC
54,137 POSTS

This can be causes by to reasons, first you have a clogged air filter or catalytic converter. I would check the air filter and if okay go over this guide to help check the cats.

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

You can remove the primary oxygens sensos to see if anything changes, also, can I ask if the engine is a turbo model? If so this can be the problem, if the turbo is worn out it will not rev at all. Please let me know.

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Saturday, September 6th, 2025 AT 4:40 PM

KDINERO

MEMBER
2 POSTS

The engine is non turbo. I unbolted the exhaust headers from the heads to see if the cat was blocked, no change. I removed the air filter, no change. I removed the oxygen sensor, no change. Fuel pump was replaced 2 days ago and there was no change either. I am stumped.

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Saturday, September 6th, 2025 AT 5:51 PM

KEN L

MASTER CERTIFIED MECHANIC
54,137 POSTS

Lets run the codes to see if any are stored, this guide can help.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please go over this guide and get back to us.

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Sunday, September 7th, 2025 AT 9:00 AM