So I bought a wrx with (what I thought was) a cat-back exhaust. Turns out it's a turbo back. And he never tuned it, just spaced the o2 sensor so it wouldn't trip the engine light. How bad is it to run my car without a tune for that exhaust? I've notice some very low idling that rises and falls at idle. The fan will click on but then immediately back off again. I've replaced the alternator but my lights still flicker sometimes. Are these all from the computer freakin out because of the exhaust?

 

i would definitely recommend getting a stock down pipe asap, or an access port/tune. Running a dp without the tune can be very harmful to your engine.

 

It has an aftermarket up and down. I have an ex scooby mechanic who will tune it for me. Will that fix it?

 

How qualified is he? A tune not done properly and with the correct equipment could be even worse than no tune. Tuning is usually something you would want to leave to a pro, or an OTS map off of an access port.

 

He's a pro. This guy knows his stuff. He built his own wrx. Guys amazing. He said he'll hook his laptop and something else up to it and it'll take like two hours. But would that help my symptoms? Like the weird idle

 

A tune for new parts is always a good idea but on 02-03 MYs you can run turboback untuned without any serious issues. If you plan to keep the car the way it is for an extended period of time, get it tuned sooner rather than later.

 

What kind of damage can it cause?

 

That I cannot answer. I can say that I have never read a thread in the past 10 years that points directly to running untuned and being catless as the source of any problem. Could this be a contributing factory to potential long term issues?? Maybe. But so could hammering on the gas pedal every chance you get- not saying you do.

Now, this is assuming you drive an 02-03, which by your avatar photo it appears you do. From what I have read newer models would have noticeable issues running untuned with your setup, mainly boost creep and possibly wacky a/f ratios, but I don't really know or care because I drive an 03.

 

Btw I would start with a smoke test to try and diagnose your idle problem. A vaccum leak will cause the car to stumble at idle.

 

I have a strong feeling its a vac leak. Now I just need to find it. I'm thinking if using the intake cleaner spray method. Do you know of any diagrams to help me locate all the hoses to test?

 

I believe the diagrams below show most of the vac lines. You'll want to check anything post MAF, so start at the bcs return line on the turbo inlet an work your way back. The inlet will have the bcs return, valve breathers return, PCV return... Also check the feed connections for these lines as well.

 

Couldn't see my typing anymore using the app...

Then you'll want to check all the post turbo/pre throttle body stuff- just intercooler gaskets and connections really and bov vac line. Then move onto the intake manifold and all the small lines that run off of that. For the hard to reach spots like the injector seats you can spray starter fluid on them to see if idle changes.

Last resort you can pressurize the system and start spraying soapy water... Which would also help you find any boost leaks just in case.

 

You're fine. You don't need a tune for it, though it's pointless without it.

On later models it can cause engine damage.