Miata Turbo Forum - Boost cars, acquire cats. - Idling at an AFR of 20-21, what's the cause?

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- - Idling at an AFR of 20-21, what's the cause? (https://www.miataturbo.net/general-miata-chat-9/idling-afr-20-21-whats-cause-26102/)

Quote:

Originally Posted by rccote (Post 311499)

Got some new developments if anyone can make heads or tales of it. Well, after driving for about 20 minutes the AFR will read ~15 at idle pretty consistently. On start up that's different, though, it will hold 15 for a good minute before it starts to climb up to 20.

When driving I've noticed some new sounds coming from the exhaust/engine. It's sort of a grumbling or gargling sound and muffled popping when I let off the gas. It sounds similar to the sounds heavily modified turbo cars make on deceleration with all the backfiring and whatnot. Granted it sounds kind of cool, it's really worrying me. Otherwise the car feels completely normal. The idle MAY sound a little different but that could be me being paranoid.

Also now my boost numbers are around 14 opposed to the desired ~12. Sometimes I can see 12 for a second and it will hold at 10.18 for about 5 seconds then go back to normal reading.

When I get the chance I'm going to check my timing, plugs, wires, and injectors. Not sure where else to look. Could a faulty AFM cause this problem?

The AFM can cause some strange situations. It would be a good idea to put your car and setup in your signature so that people know what you are working with.

I figured it could have been unburnt fuel, I'm suspecting a faulty injector but I'm sure how to identify which one. The best I could do is swap back in my 1.6 injectors and see if that makes a difference. It's pretty confusing because it runs and sounds completely normal under acceleration and cruise. But I did notice that the idle sound is in fact different now.

Have you pulled your plugs yet?

Ok, you need to list your setup. What injectors are you running? How are you controlling fuel/spark? What is your fuel pressure at idle? etc etc etc

Help us help you.

Apparently it hasn't shown up in my sig. Now maybe?

Quote:

Originally Posted by Mach929 (Post 308908)

vacuum leak?

Correct!

Found a torn vacuum hose. Fixed it and it runs like normal.

Quote:

Originally Posted by rccote (Post 312638)

Correct!

Found a torn vacuum hose. Fixed it and it runs like normal.

ALWAYS look to the simplest things first.

Quote:

Originally Posted by olderguy (Post 312924)

ALWAYS look to the simplest things first.

I thought you re-build the engine first .... then look for vacuum leaks :)

I had already checked the hoses before because I had to take the valve cover off and the hoses were fine so I never gave it a second thought. The tear was on the underside and I suppose just got bigger and bigger until it started to cause problems.