Not quite a 911, but would like a preliminary diagnosis

[Gator Jeff]

Alright, well the cold and my health have forced me to hold off on my full tune-up, but my X is having problems.

For a couple weeks prior, I was experiencing a very rough idle at start-up and some hesitation when cold. Fine in the higher rpms and when cruising. On Tuesday, I threw a CEL. I got home, disconnected the battery, cleaned both the IAC valve (filthy) and the MAF (a little better) with the appropriate cleaners and re-connected the battery. Ran much better, much better idle, but threw a CEL on my way home the following day.

Now, it still idles a little rough in the morning, a little rough at lower rpms and my exhaust smells like burnt coffee after leaving an empty pot on all day.

I'm getting in the zone tomorrow and getting my code flashed, but I'd like to have some ideas tonight from the late/overnight crowd as to what codes/issues to expect and how to address them so I can get right to work tomorrow when I get the code. Thanks! It's a 4.0 OHV with 125K BTW.

 

[nssj2]

Howdy! Unfortunately its pretty much a shot in the dark without the code. Id think maybe an o2 sensor though. How is your gas mileage?

 

[Gator Jeff]

I think I've lost a few mpgs so down a good 10%. I know its all guessing right now, but I'd rather have some ideas now than get the code first thing in the morning and if I can't find enough info, wait until most folks wake up to get an answer. Thanks!

 

[G-96XLT]

just get the codes , it is impossible to say but it will most likely be a sensor or a supporting part such as a thermostat or egr valve. the code will only tell you the general heading of the problem , don't replace the part right away just because the code says something. I got a p0125 the other day and it could have been the sensor or the theromostat or the cap. I had to diagnose it further and found it was the tstat and the code cleared and the car ran much better.

 

[Gator Jeff]

and I'm remembering reading something about voltage reading for sensors. is that what will ultimately tell me the culprit/culprits?

 

[nssj2]

usually bad smelling exhaust + bad idle + bad mpg usually = o2 sen or cat converter. good luck!

 

[Gator Jeff]

Code was a P0304. Misfire on #4 plug. Pulled plug and was cracked around the base. Replaced all plugs and wires, new gaskets on intake plenum and I can't remember when she ran this smooth. Thanks for all the suggestions!