I am getting miss fire code on 1, 2, & 4 when at driving speed.
I changed the spark plugs and pcv valve about 1 month ago and everything was fine. Now, i get check engine light and hear noises and shaking in the engine compartment. And at start up it is slow to get to speed and stutters. when stopping rpm drops to 250 before getting back to 750 ish.
Is it the coil, injector, or position sensor?
Any help will be appreciated!

 

Most likely a coil.

I would buy 1 new coil and replace the #1 cyl with it, reset the cel light and go for a drive, see if it clears it up. If not take the new one and put it on #2 and repeat till you get to #4 and see if it goes away. Its highly possible you have just one bad coil causing it (these cars are known for throwing multiple misfire codes for just 1 coil)

 

Yea most likely a coil. Same thing happened to me a few months back and all you really have to do is pinpoint which coil it is like he said cause it's usually just 1 that's bad.

The way I figured it out was to let the engine idle for a few minutes then start to pull one coil at a time and each time you pull one check if there's a change in your Rpms (either they drop or nothing happens). Do it for each one and the one where nothing happens (no change in Rpms) is going to be the bad one. Make sure to reset the ecu after u replace the one that's bad. If it helps the way the coils are numbered is from the back passenger side near the firewall that is numbers 1,2,3 and toward the radiator side starting from the passenger side it's 4,5,6. That way you know which coil number it is when you pinpoint the bad one. hope that helps!

 

Thank you for your advise! Will try it and reply.

 

Instead of pulling the actual coil out each time, you can just pull the plug off as the motor is running. Just be sure to plug them back in as you go. There is no need to clear the CEL after each pull and plug. Just be sure to reset the ECU after replacing the bad coil.

 

STOP!!!!!!!!!!!!!!!!
EXACTLY what spark plugs did you install?
the CORRECT ngk iridium or ngk iridium IX, or ngk Platinum, those all cost about 8 dollars PER PLUG
(denso also allowed but cost more)

IF you installed bosch - acdelco or other 2 buck plugs- thats your
primary issue- they are fried

Replace with right parts and reset ECU- drive and test for coil prob
Its easy to damage a coil during plug change and it fails a month later
treat them like fine china,,set down gently--electronics inside!

 

Thank you all you guys!!!!!
Your advise really helped.
It was cylinder 4 coil after all.
I did change all the spark plugs to ngk iridium too.
The Bosch Platnums didn't look too bad though.
Any way, thanks to all and God bless!!!!!