I have a couple problems with my 2004 3.0L manual V6 Ranger. First, it idles rough, sometimes to the point where I think it is going to die, but it doesn't. Second, it seems to only want to start when the temperature is mild and the humidity is high from just general observation. Now for the background.

I bought the truck used in 2006 with something like 30K miles on it. I drove it a few miles to work everyday for a few years, then, I changed jobs and started driving much further to work everyday, as well as taking trips of about 400 miles every couple weeks. This continued for about 10 years. I kept the oil changed about every 5000 miles, replaced the air filter every couple years, and performed other maintenance as necessary during this time, though the only problem with the engine I ever had was a dead battery that I had to replace only once after about 7 years of ownership. In 2019, I had a couple times where the engine wouldn't start. It acted like it wasn't getting gas. After a few minutes, it would start right up with no problem. I did notice a very slight bit of roughness to the idle as early as 2018, but it was hardly noticeable. Later in 2019, the alternator went out, so I replaced it, and a month after that the battery died, so I got a new one, which did not appear to really affect performance at all (obviously, I could start the truck just fine). A month after that, I decided I would change the oil. Nothing unusual happened, except I might have put a little too much oil in, but not a huge amount over. The next day, I drove the truck about 80 miles to work and back with no issues. The same day after work, I drove to a restaurant to get some food. While waiting in the drive-thru lane, the check engine light came on and the truck nearly died. I had to keep my foot on the gas when out of gear to keep it from dying. I managed to make it home, and put an OBD scanner on it to find out that it had codes P0301 and P0316. I researched the codes and read some forums on here. The short story is that I replaced several parts, but still have issues. Some of these parts were the spark plugs, plug wires, ignition pack, pcv valve, camshaft position sensor, and fuel filter, in addition to the battery and alternator that I replaced prior to having problems. I've also had the compression checked by a mechanic who said that everything was fine, but another mechanic at the shop said the rough idle was "just how Rangers are". I've also swapped the fuel injectors around, but didn't really notice anything in terms of error codes, and the fuel pump seems to be pumping OK (I haven't checked pressure though). All injects seem to be functioning as normal too, at least from what I can tell from listening to them.

The truck had about 185,000 miles on it when the problems started. It still idles rough, but no CEL is on and the error codes don't show up any more. I've checked for vacuum leaks, but haven't found any. In addition to the rough idle, the truck has the intermittent start problem, which I used to attribute to hot days, but now, I think it is more related to humid weather, with it starting better when damp (very odd). It tends to start better when the engine is cold, though like I say, on cool days, it will start even with a somewhat warm engine if the air is humid. Also, it doesn't struggle to start. When conditions outside are right, it fires right up. I haven't really seen changes in fuel economy either, nor do I smell unburned fuel in the exhaust, except when I first start the truck, which is expected. I still drive the truck about once a week, but it isn't reliable anymore.

Any ideas as to what might be wrong?

 

Were you able to find out what was wrong with your truck?