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Dan
Dan, ASE Certified Technician
Category: Subaru
Satisfied Customers: 1611
Experience:  Auto Technician
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Got a 2006 Outback XT. Just put a rebuilt block into it.

Customer Question

Got a 2006 Outback XT. Just put a rebuilt long block into it. Idles very rough, like misfiring. But no codes or CEL. Bought it with bad engine, so could be something unrelated to engine swap. Fuel is very low... would bad fuel do this? Have rebuilt about 20 Subaru's, but haven't seen this before. Thoughts?
Submitted: 5 months ago.
Category: Subaru
Expert:  Dan replied 5 months ago.

Hello my name is***** am an ASE Master Technician and I am glad to help you out with your question.

Expert:  Dan replied 5 months ago.

Check for vacuum leaks, the pump going from the air box to turbo is common to crack and take in unmetered air. Also check the pipes going to the intercooler.

Use a scan tool to check fuel trims at idle and let me know what you have.

Expert:  Dan replied 5 months ago.

Does it idle high?

Customer: replied 5 months ago.
No, doesn't idle high. Idle about right RPM, but very rough...like a misfire. I don't have a scan tool to test the fuel trims. Also, what's "the pump going from the air box to turbo is common"?
Expert:  Dan replied 5 months ago.

Sorry its "pipe" seems the auto correct changed the word to pump.

Disconnect coil packs one at a time while the engine is running to see which cylinders are missing. If the engine does not change you found the bad cylinder. If it stalls or idles more rough you know that cylinder is firing.