07 sahara has spark knock and is imo slow return to idle. I expect two seperate issues here. Has a supertuner,but still knocks nomatter what setting I use. Has oem plugs again,still no help. Eng seems to be derating at times and isnt as torqie off the line as it used to be. Not throwing codes either and no dummy lites..any ideas? Just bought new knock sensor,EGR,map sensor and upper 02 sensor to put on this afternoon..

 

Also has no miss at all,very smooth idle

 

Try cleaning the throttle body and mass airflow sensor. There's a thread on how to on here.

 

Both are new

 

Interesting. The JK 3.8 doesn't have a MAF sensor.

How about a video of the tach coming back to idle. The throttle is programmed to not come back too rapidly.

 

Correct,no MAF sensor but it does have a MAP sensor top rear of the intake. However, after replacing that sensor and the knock sensor and EGR , most symtoms are gone. I found a damaged wire harness for an o2 sensor where it had rubbed thru and was touching the foil heat shielding under the floorboard,will swap it out in the morning.

 

make sure you're using E10 blend fuel and not E15.

Try adding a bottle of octane boost - like Lucas 104 boost - make sure the additive you use is safe to use with ethanol or it will make it worse, don't use HEET moisture displacement

 

A few questions...
What octane fuel do you use, and what setting on the tuner? Does your Jeep use oil? Have you tried a carbon removal treatment?
I would bet you have some fairly heavy carbon buildup on the valves if you are experiencing spark knock, especially running the stock tune.

 

Mid-grade fuel when possible,( never use ARCO or VALERO), right now tuner is set for 87 octane but have also tried the performance settings (91,etc). Does not use or burn oil at all,engine has less than 40k on it. Spark knocks taking off from dead stop,more so if A/C is on. Thinking it may be in the gearing. I take off in 2nd gear as first gear way too short for the 5:13 gears and 37's,but 2nd is almost too high, could use a happy medium.

 

I believe the hanging idle is likely caused by the spark knock. I experience the same in my JK from time to time. (When spark knock occurs, timing is pulled - and I suspect other engine tuning parameters are altered or affected).

When my JK pings, It's usually because it's super hot out, or my plugs are worn. I run them at a tighter gap than factory - .050". (What the NGK's I run are pre-gapped at) - and this helps a lot. Your engine is only at 40K, so I would expect plugs to be ok.

Even if it still pings, I'm personally hesitant to think something is wrong. I normally just assume I have to run higher octane gas in the hotter weather. Many of my vehicles have done this.