Hesitation at idle after highway driving

[TigerBill]

I've noticed recently that if I drive my car at 60-65 for 5 minutes or so then come to a stop light, it idles rough. The other day it actually stalled on me. My brother says I need to check my spark plugs, doing that tomorrow. I went to Autozone and they pulled a code 34 (KS) that guy also said check spark plugs.

I dont think the KS is bad as I' not having any probs with acceleration or gas mileage, as I read on here that those are signs that the ECU retarded the timing for a knock. Today I got a CEL, Nistech says KS wont throw a CEL, so Im wandering what else could it be. Im going to take it back to Autozone for a code scan, but thought I'd check here also.

Its a 96' 240sx se, auto, w/ AEM short ram, Hotshot header and BRM 2.5" exhaust w/ highflow cat. I bought the header used with a O2 sensor in it, Im wandering if that could be going bad too. On a side note I've been using oil recently bout half quart every week or so. Dont know if its burned or leaked. Im assuming burned as my exhaust tip is all black. Sorry for the long post just dont want to miss any info that might help. Thanks in advance for any and all help. I'll report tomorrow what I find with the spark plugs.

-Bill

[TigerBill]

Ok, so I went to Autozone again and this time the code34 (KS) was gone and the comp said it was running rich. I pulled the plugs and they all looked good, my dad who is a mechanic even thought they looked good. I replaced them anyhow with some NGK Iridium IX's and it seems to be running real good. I'll know next week if I still have the hesitation problem. Guess next I'm going to replace the O2 sensors. If anyone has any ideas please let me know, or at least tell me I'm an idiot.-Bill

[NISTECH]

The o2 may be phase shifted rich and the ecm is trying to compensate by leaning it out. It may be leaning it out to the point it kills the car on decel. The best way to check this is to go in and watch your 02 cycling in the ECM there is a write up on how to do this on 240sx.org[our sister site] look in the FAQ section for endine codes DOHC.