I bought a 1993 ranger 4x4 4.0L automatic last summer with 100,000 miles. I changed the plugs and wires, checked all the vacume lines pcv valve ok. The engine runs good and doesn't smoke but when warmed up seems to idle a bit rough with a little shake, rpm about 300-400. I have even had it stall at a stop light at times but at highway speeds or towing it has no problems and lots of power. How many miles should I expect to see with this truck? I hear that they were tough engines. Maybe it's just age?

 

Well the rough idle could be a number of things, but with the items you've gone over & you not saying you have any trouble codes, I might put the IAC (Idle Air Control) on your suspect list.

Some have had luck cleaning it, some say it didn't last, others say cleaning it didn't make any difference at all & replacement was the fix.

Intake manafold gasket leaks are common on the 4,0L too. So if a IAC test, or cleaning doesn't pan out, maybe do a propane sniffer check, around the intake manafold & vacuum lines, including the PCV.

BTW, if the PCV hasn't been changed, think I'd pop a new one in there anyway, as a 14 year old one, has to be tired & remember it's a controlled vacuum leak, so it needs to be doing it's thing right!!!!

Just some thoughts to ponder.

 

Thanks for the info, I just had the truck warmed up and tested the IAC by unpluging the connector to it and the idle went down to almost stall speed (according to the haynes manual) it tested ok but will still take it out this week and clean it, also a new pcv and see if that helps.

 

BTW welcome to FTE tomater.

After re~reading your initial post I realised you have the 4spd auto tranny. So next time it tries to stall, when or after coming to a stop, try quickly shifting into "N" & see if that stops the stall or rough idle. If so it might indicate the torque converter isn't unlocking. Thats sorta like trying to stop a straight drive, with it in gear.

If the tranny fluid & filter hasn't changed, it's likely time for that also. There is a how to link in the "Tech Info" thread atop this forums thread list page, lots of other helpful info there, so be sure to check it out.

Seeing as how it has 100+K mies on it I'd bring it up to date on all past & present scheduled maintenance items listed in your ownes manual & you've already done some of them, like plugs & wires & are going to do the PCV valve.

Other things like fuel & air filters, fluid changes for the power steering, brake fluid, coolant system flush & antifreeze change are on the consideration list too.

I know some of those don't have anything to do with your rough idle problem, but the fuel filter, air filter, tranny fluid & filter may be playing a part & are scheduled to be changed anyway, so it's not a waste of time or money to do them.

The rough idle & stall could be caused by a number of things, from a vacuum leak in the upper or lower intake manaflold gaskets, vacuum lines, vapor recovery system, acting out PCV system, to a misbehaving EGR system, to a sticking torque converter lockup solenoid, to.... well you get the idea,

We will likely need some more good clues to run it down. So keep the clues coming.