I am having trouble with rough idle in a 2001 Ranger 4.0L. It all started like this: Truck would not crank on Monday morning as battery was dead. Got a new battery and went ahead and changed oil since I was due and late for work anyway. Filled up with gas and added fuel injector cleaner.
On the way to work, got Check Engine light and started with rough idle. Had codes scanned and got P0171 and P0174, both indicating fuel too lean. I changed fuel filter - no luck. Filled up with premium gasoline - no luck. Unplugged MAF sensor and found that engine idled fine without it. Bought new MAF and installed - no luck. Engine sounds like it wants to go dead when stopped and rocks and shakes at stop lights. Gas mileage is suffering.
You could try to change the O2 sensor(s).. They are alot cheaper than the MAF, and it seems to me, on my little truck, that is usually the culprit. It's one of the points that tells the comupter how "lean" or "rich" the engine is running. If some crude got knocked loose than it could've "latched" onto the sensor. Some of the injector cleaners say "safe for O2 sensors" or at least all the ones I've seen do.
You'd be suprised how many times those (O2) are the answer to why it's running like crap..
Thanks PPR! I actually found a leak on a rubber 90 degree hose that is located under the throttle assembly. It is attached to a rigid plastic/rubber line that runs the length of the valve cover on the left side when facing the engine from the front. The rubber boot elbow in to the intake. I replaced it and that has smoothed out the idle significantly. I haven't had the check engine light come back on yet, but I may see if I still have any codes that haven't been resolved.
I am still not entirely happy with the idle, but it much better than it was. If problems continue, I will be looking closer at the O2 sensors.