So my 2002 nissan xterra 3.3 supercharged began lagging up hills months ago, but I ignored it. Now it sputters, lags, RPMs jump from 1000 to 1500 at idle, and sometimes dies and has a hard time starting back. Usually at higher RPMs its fine, but it will still do it then, and when it does... it tries to backfire. No engine light. I had it scanned it read IAT (intake air temperature) sensor and knock sensor. Mechanic tried to get me to order the wrong sensor because he never heard of an IAT Sensor. I googled it, found out where it was and ordered it and installed it myself. For a day it was fine, then it all started back over and worse. The knock sensor might require me to take off the supercharger and manifolds among other things in the way. If it is the knock sensor, could a relocation of the knock sensor work or will it make more problems in the future? Also, I read that it might not be the knock sensor, but another problem that is causing the knock sensor to read bad? I heard some say its the idle valve/sensor, MAF sensor, Distributor, or something with the fuel system like a sensor or filter. I dont know why its not showing a check engine light and I don't want to change out 20 different things before I find the right thing... but that is the way of neophyte mechanics I guess.
I would start with the basics: good spark, good fuel pressure, good cylinder compression, unrestricted intake and exhaust path.
You have to ask yourself what is causing the knock sensor to detect the detonation. Here is the definition:
The engine's knock sensor (or sensors) detects preignition and detonation, potentially damaging forms of abnormal combustion. Though full-blown knocking and pinging are audible to the human ear, the knock sensor detects imperceptible levels.
The ECM is just telling you the knocksensor has detected the above conditions. Now you ask is the Knock sensor bad ? Maybe its too sensitive is more the possibility. Some things you might trry is to fill your vehicle with the highest octane gasoline and see (if any) thing changes after clearing the codes. You say it has a hard time starting up...theres a hint. Is it ignition or lack of fuel. Check the fuel pressure with a gauge and what is it - what is the expected pressure value. other things come to mind...clogged cat converters. Pull out the oxygen sensor on the engine side and let it run..will it run better or the same. basically its a shotgun approach but what your doing is if some component is operating correctly then you dismiss them and go to other which are suspect until proven working as intended. You could just find the wire that leads to the knock sensor and unplug it to see if that would make any difference without yanking any intake manifold as a test to see if anything changes.
