2003 Protege DX 5MT rough idle
 

Hi! This is my first post on this forum.

I just bought a 2003 Mazda Protege DX Manual transmission 170k miles and have been having issues with rough idle. At emissions it threw a p0303 CEL light for cylinder 3 misfire.

I noticed a small pool of oil near the #3 spark plug boot, took boot out, fair amount of oil on it as well as oil on #1 cylinder boot. #3 spark plug looked the worst of all 4. Replaced valve cover gasket along with dabs of RTV by sharp corners near cams, spark plugs (NGK V-power), and I removed EGR valve for a good clean (soaked an hour in carb cleaner, oiled valve shaft, replaced). Also cleaned out PCV valve as well. Computer has been reset several times, always disconnect the neg battery cable before working on cars,

The car still gives me rough idle after being warmed up, it actually almost stalled for the first time today after EGR clean.

I have searched on this forum for rough idle threads, EGR clean, etc etc. I was just wondering if there is anything else I should try before I buy new coil packs and wires?

TIA,
Thomas

With the engine running, spray brake cleaner all around the intake manifold, listen for any change in engine tone, this would indicate a vacuum leak.

UPDATE::

I sprayed TB cleaner around IM - no apparent leaks / idle did not raise. Thanks grim_reaper for the suggestion. I did however peek at the air filter for the first time - and it looked like a dryer filter that hadn't been cleaned in two weeks! I replaced the Fram filter with a Purolator, and the idle / hesistation problems were nearly absent.

I couldn't get the screws on the IAC valve off to clean it ( 1 hour, 3 coats of PB blaster, using #2 phillips head and hitting screw driver with hammer while turning). You REALLY need an impact wrench for this. However I did get into the TB and spray a good amount of Choke / Carb cleaner. I bent the little red straw so the fluid would hit the top of the inside of the TB where the IAC valve is.

However, last night while driving i got P0507 "Idle Control System RPM Higher Than Expected" code. I must have loosened something up by spraying the inside top of the TB, or it could be the new air filter. My car has been sitting overnight with negative battery cable off, and I will update as this progresses.