Rich or lean?
 

Hey all, just wondering the characteristics of running rich or lean. I'm not a super experienced wrencher (brakes and oil changes mainly although I want to get into doing all my own stuff), but I feel as if my car isn't performing optimally or close enough to 14.7:1. I recently switched from a high-flow cat to a straight pipe and since then I've noticed lots of exhaust smell in the cabin when I'm driving (particularly at startup). Starting is usually a little rough when it's hot out (Texas weather), and then the car will go on to idle around 1400rpm when it's set to 1000.

I was planning on changing the O2 sensor within the next coming weeks anyway seeing as it's supposed to be regularly replaced, but I was wondering if the above issues pointed to anything else? I'd be happy to give more info if needed. Hopefully someone can help me chase down this small gremlin!

I would check if the straight pipe you put in has a leak. You shouldn't be smelling anything in the cabin check your Wastegate for leaks also. As for running rich or lean, with the increased exhaust flow and no other changes you should be running a bit lean. What are the mods on your car?

Catless cars stink there isn't a whole lot you can do but learn to love the smell and make sure your cabin is sealed up, especially the rubber around the hatch
When cold the car will run rich to get up to temp faster so the fuel scent will be stronger

Give it an idle reset according to Clark's Garage. Let the oil get up to 150 F minimum then jump the test ports and set idle.

Believe it or not, this procedure has on occasion made fumey cars behave better, and it only takes a few minutes.

The smell on startup could also be an oil leak on top of the crossover that smokes off as the car is warming up.

Exhaust leak obviously an option and you could run it by an exhaust shop.

Sounds like you might have multiple issues. You should not smell exhaust in the car with or without a cat. Fix that first -- it can be dangerous. A leaky rear hatch seal is a common source of that. If you have an exhaust leak closer to the motor, you can also suck it to the cabin with the HVAC system if the air recirc button is off. See if it goes away by pushing in the recirc button. If so, looks for leaks under the hood, maybe at the downpipe to test pipe connection since that's the last thing you touched. After a while, soot will build up around leaks and make them pretty obvious.

For the high idle, do the factory reset procedure. And if it still runs fast, then most likely the cause is a vacuum leak (or an aftermarket maf system that isn't happy at factory idle speeds). That could also cause the start-up roughness too... No guarantees of course, but that's a good place to start.

Awesome replies everyone, this is super helpful to me. I'll be giving as many of these a try as I can this weekend. As for now I'll drive nice and easy on the motor so nothing changes.

As an aside, we have almost the same 951!!

Really cool! I don't know why the mobile app doesn't show signatures. PM your VIN to me - if yours is 89, we'll see how close they are. -Scott

I like my women rich and lean! :) carry on...