I have a 1990 Ford Ranger, 4.0 v6, 4x4 that I am having idling issues with. Specifically, when in a low gear, it surges and sputters like it wants to stall. I have done the PCV valve, new spark plugs and wires, fuel filter, air filter, and the idle air control valve. When I am in neutral or park the problem is not quite as bad, but when I am in gear, especially sitting at a stop light or stop sign, it idles rough. Does anyone have any recommendations on what the issue might be caused by, that I have not already addressed. One thing I think might be an issue would be the vacuum lines. Am I on the right track? I have also upgraded the exhaust and done routine things like oil change and fluid checks. Thanks in advance for the help, it is much appreciated.

 

Welcome to the forum

Recheck Coil Pack wiring, it often gets reversed wires on the drivers side

Coil pack
3 4
2 6
1 5
Front

The 5 6 4 side often has wires in the wrong order
Follow each wire to its cylinder on the drivers side

Ford numbers cylinders on a V6 this way
3 6
2 5
1 4
front

Spark plugs should have been gapped to 0.054, its a wide gap but needed on the 4.0ls

Try a can of Seafoam in the gas tank, I need to do this once a year on my 1994 4.0l to smooth out the idle, injector tips get dirty and DRIP fuel at idle, instead of spraying fuel, so pour air/fuel mix at idle, but wouldn't effect driving, just at idle

A vacuum leak will usually cause a higher than normal idle, do you have that symptom?

Do you still have the old spark plugs?
Have a look at the tips of each to see if they show any specific cylinder with a darker tip, oil burning
Or white tip, coolant burning

 

I will double check the wiring. The only way I would have gotten it wrong is if it was set up wrong prior to me being the owner (which I am not ruling out). I will also check the spark plug gap. It could be possible I tightened them too much when installing.
The Seafoam is a great idea, I'll also do that.
I do NOT have a higher than normal idle, so hopefully it is not a vacuum issue.
I got rid of the old spark plugs, not realizing how telling they could be of a potential problem.

Thank you for all of the help and advice. I'll check all of these issues and report back.

 

Any one who has worked on multi-cylinder gasoline engines for more than 5 years will have F'ed up a Firing order, and SWEAR THAT IT IS RIGHT, lol
It is just way too easy to do and even easier to overlook

 

Think I finally figured it out! My wife's step-dad works at a garage, so I took it to them when I ran out of things I could do myself. I did the seafoam treatment, with not much luck. They initially replaced the mass air flow sensor, and for about a day it ran better, but then the issue came back. They ended up replacing the fuel pressure regulator, which was causing my issue. At this point, things seem to be much better. I watched a youtube video after the fact, and all of the symptoms I was having could have been a direct result of a bad fuel pressure regulator. For now, things are running much smoother. Thanks for the help.