interim rpm fluctuation

[apt216]

when first starting my 1992 240sx the engine rpm fluctuates then stops and starts again while driving at lower speeds in town, at higher speeds 65mpg and up it seems to be ok until i begin to decelerate. I have replaced the cap and rotor. also check for any codes and it showed a code 34 which was a knock sensor failure, which i replaced. also check the fuel pressure and it was at spec. even when the fluctuation of rpm was taking place the pressure stayed normal at 36 psi. what should i be looking at next? thank you

[pepesilvia]

this happened to me too. i had code 34 and replaced EVERYTHING, injectors, plugs, wires, sensors, cap and rotor, fuel pump etc... after this happening for about 6 months i pulled my spark plugs again and found one of them was charred. I bought new spark plugs again and realized that i hadn't tightened the spark plugs properly the first time and when the engine would fire in one the cylinder's, the explosion was seeping through the loose spark plug and causing hesitation in low-RPM acceleration.

pull yur spark plugs and you'll be able to tell if your car is running lean/rich and you may find out that u need a new fuel pump, injectors or spark plugs. they are the common culprit apparently.