rough Idle and horrible mpg

[mnofal225]

So everytime i am at a stop light or at idle my car vibrates a little and when i rev the engine its a little rough until it gets to about 2500-3000 rpm then it purs like a kitten. i replaced some bad gaskets in my exhaust. Seafoamed the car twice, put new spark plugs, run only premium gas, put a blitz cone filter (off my friends rb25det) and i dont know what else to do. do i have to go to the idle control valve and adjust it.
Also my mpg is like 14-16 and even after all these upgrades its still bad. (i know the 300zx should not have great mpg but it should not be crappy either)
should i still seafoam it one more time because i had alot of gunk in my plenum. my car has 170,000 miles and is NA
if anyone has any solutions on both problems i would greatly appreciate it.

[johnshop]

check injectors, and coilpacks.

[mnofal225]

check injectors, and coilpacks.

how do i check that exactly ?

[johnshop]

well i am not an expert, but you have to do whats's called a power balance test.

it will tell you if you have a dead cylinder in which case it can be a bad injector, bad sparkplugs, or a bad coil pack.

read this thread: idle-engine-problems-t524711.html


here is a thread to help you get the idea on how to test coilpacks: testing-coil-packs-t542851.html

[nissanfreak12]

Power balance test, pull the coil packs off one at a time, if you don't notice a difference in the way it idles, that could be your issue. You can ohm test the injectors as well, search is your friend, there are ton of info about this.

First thing to do is check the ecu for codes. Don't just rely on the CEL coming on, you have to physically put the ecu in test mode.

https://www.google.com/url?sa=t&rct=j&q ... 5884,d.aWc

This is always the first thing you do when you have an issue with your car, its easy, free, and most of the time points you in the right direction. Post what you find.

[mnofal225]

so this an update on the situation.
this morning i tried to figure out how to unplug the coilpacks and while i was doing that i noticed that they were very dirty so i cleaned out all of them. after that i turned on the car and did the whole power balance test and everything was normal. i then took a spin in the car and i notice no more vibration and more HP and much better response. I guess i fixed my problem and as for the mpg it seems to be better but i wont know for sure until i finish the gas tank and do the calculations.I will update on my mpg
What should be the MPG roughly

[johnshop]

there you go man, you got lucky it was just dirty connections. good stuff!

[nissanfreak12]

16-22 MPG depending on how much you abuse the skinny pedal