a miss that isnt constant

[novarider]

hi im new to this forum i have a 95 240sx and it is missing, but not all the time, and the check engine light is on so i went to the shop and they told me it was a bad egr valve and a knock sensor. but they told me to do a tuneup and see if that fixes it. i also have that rattle noise from the timing chain so i was wondering if it could be that the chain is so loose that it is the reason for the miss? the miss started after i replaced the alternator and when i replaced the altenator i forgot to plug in the wire and the battery died and i had to replace it then got the wire hooked up and then was driving and the miss started is the altenator just a quaincadince or what i really need some help thanks for any replys

sorry if you see this twice i found out i posted in the wrong place so i posted here after

[slipnfall]

Does it only miss at idle, or does it also stumble while driving?

Some general Nissan tips: if you're bothering doing a tune-up, use only NGK spark plugs. If the auto part store doesn't have them, then make them order them. Don't buy into the 'V-power, split electrode, 4-electrode' BS. It's what the factory calls for and anything else just seems to be trouble. When it comes to the cap/rotor: OE only. It's not *that* expensive, and these are critical parts.

Regarding the mis: if it's only at idle and intermittent I run through your engine bay and do some wiggle tests on various harnesses, especially injector plugs.