Best procedure to tackle misfire codes? (1 Viewer)

[elk]

My new to me 2006 exhibits hesitation on hard acceleration but rolls along happily at highway speeds. I am averaging 12.6 mpg with conservative mixed driving (a little low even by LC standards) on 87. My CEL/MIL is off. I have a high idle at initial startup that normalizes when restarting warm. Oil color seems normal (so no H/G leak I presume). Coolant level consistent after 1500 miles, oil likewise. Thermostat reads mid low, oil pressure 1/4 (I hear the sending units are iffy).

Naturally I hooked up my code reader and pulled up the following codes;

P0300 - random misfire
P0100 - mass or volume airflow circuit
P0102 - mass or volume air circuit low input
P0103 - mass or volume high input
P0125 - insufficient coolant temp for closed loop circuit

Now, being diligent and not wanting to anger the MUD knowledge base, I searched steadily. I would like to approach the most likely cause first.

P0300 and P0125 made me think of the O2 sensors. My vehicle has 176k miles, and so I figured I would start by replacing them. All 4 new Denso sensors are in after an evening's work. The vehicle seems to drive smoother, but the hesitation is still present. I had previously pulled bank sensor codes on occasion for the cats, but these are now gone so I suppose this was addressed.

I cleaned my MAF with specific cleaner, no improvement.

This weekend I will likely address new spark plugs, PCV and possibly the thermostat as I am still baselining. What should my next course of action be?

Inspect for vacuum leak? - free
New MAF? -$
Check injectors?-$$
Coil packs?-$$$

Thank you in advance for any advice.

 

[Slickspawn]

Swap around coils. Disconnect coils and see which one makes no change.

 

[MichiganLandy]

Call me crazy but make sure your airbox is properly fastened/closed.

I have an newer Crown Vic and after the dealer changed the oil one Saturday... Bam! I would get a big lumpy stumble at idle. No check engine light either. Assuming the worst I started throwing parts at it. changed spark plugs...stumble stayed. Changed the coils... nothing. As I leaned on the airbox to check something else, the top half moved about an inch. Long story short, they didn't close the airbox correctly after checking the filter and the computer couldn't adjust for the amount of air it was getting. Funny thing was, I was getting NO MPG difference or other drive ability issues around town or on the highway... Expensive oil change! lol

Just a thought.

 

[elk]

^^^I appreciate this, however it was not the case. It certainly didn't hurt to check.

Could P0125 be a thermostat issue if the engine seems to run slightly cool? Thermostat stuck slightly open?

 

[Scottb4857]

Well, thermostats are cheap and easy to replace - so put one in. If you've already put new coolant in just make sure you have a clean bucket to drain via the petcock then use a paint strainer in the funnel when pouring back in to catch anything that may have fallen into the bucket.

Make sure you have well cleaned the throttle body, build up in there can mess with the idle big time. Be sure to take apart the PCV connection on top of the throttle body and clean it out also. Seems mine was almost blocked. Of course clean up or replace the PCV valve while you're at it.