My Evo 9 suddenly started to miss fire and running rich all of sudden. It 1st started when the weather started getting hot.

I've tried to lean it out some but, its still having a hard time on idle. I've checked compression and they are all 180psi. Any info would be great.

 

Check plugs, wires, coils. I had similar issue, but at higher RPM's. Turned out to be plug gapping.

 

I already put new spark plugs and still doing the same thing. The old plugs looked dry,with carbon build up.

 

How rich is rich? Do you have a wideband in the car?

 

There could be several things to cause this issue, first one that comes to my mind would be your Fuel /Air temp comp table, next could be that your AIT sensor is failing and reverting into the fallback value. If this just happened when the outside temps climed there is an logical answer to it.

 

Is this jsut a startup/warmup issue? As GTVEVO suggested, the first place I'd look is the fuel/air temp table. Check the Idle template for any weird settings that would richen it per temp.

 

Another sympton is that at start up I have to give it gas or it will die. I'll check the fuel/air table and air temp sensor.

 

Play with the RPM vs Start table. Add RPMs for the first 20 seconds or so after engine start. I had this issue with the damn thing stalling on me if i didnt give it gas. Played with this table for a bit and no more issues.

 

im having similar problem.... car will be idling fine 14.6-14.8 then it hiccups and its gets real rich for a second then goes back to norm... it happens once in a while sometimes twice in a minute... any ideas??

 

Post your datalog when it does this!

 

They need to pull from internal log... you might have to read intructions to do this

 

This sounds eerily similar to what mine does, but my AFR's were richer starting out.

For no rhyme or reason my injectors go to full duty cycle for an instant, then back to normal. I've attached a log where I caught it.

edit: crap, it won't let me attach a .stf file...

 

Maybe a bad injector than? I do get high IDC with the boost I'm running. Maybe after working to hard so many times its starting to give

 

I responded to the original question and just realized that it was posted 4 years ago.