93 ranger rough idle 4.0 elt
 

I have a 93 ranger 4.0 a4ld . It has a rough idle and surge some times. There are no codes present. When it surges the check engine light comes on but goes off when it stops surging. Can any one help me please It also passed a smog check here in California last month with this engine miss. That just seems weird to me.

I would do these things:
Clean the MAF sensor
Clean IAC Valve
Check gap on spark plugs, 0.054
If spark plug wires are original replace them, Motorcraft wires last about 10 years

Run a can of Seafoam, or similar cleaner, in the gas tank; do this once a year, always smooths out idle on my 4.0l OHV

How to clean IAC Valve seen here: https://www.explorerforum.com/forums...-w-pics.84220/

Pay attention to spark plug wiring on coil pack
3 4
2 6
1 5
Front

The 5 6 4 side often gets mixed up, at the coil or at the cylinders

Thank you for the info. I will try those things

The problem ended up being the heated 02 sensor fuse. I put in a new fuse and it runs great. I hope this will help some one else.

Having a similar issue with my 96'. if that fuse was blown...wouldn't it throw a check engine light?

In 1996 it would, 1995 and up Rangers had the newer EEC-V 104 wires computers, OBD2 protocol and it monitored everything, well just about everything, lol

1994 and older Rangers used the EEC-IV 60-wire computers, OBD1, and while it did monitor some systems it was slow to react to most issues, and yes it should have set a code if O2 heater circuit failed, but OP may not have had a reader or CEL bulb may have been burned out.

understood

Same issue here!
 

RonD.....MAF cleaning? spray out with carb cleaner? I've done all of your suggestions except for clean MAF and seafoam.....I also replaced my IAC valve because it would make a horrible noise intermittently....after i changed the valve and gaskets, at part throttle I get a whistle that i believe to be a vacuum leak....but can't narrow it down because it only does it under load in gear.....@1800-2000 rpm.

No, not carb cleaner on MAF

Electronic cleaner, no residue, they also sell MAF Cleaner at parts stores, but you pay a bit more that for electronics cleaner, but same stuff

Carb cleaner would leave a residue preventing MAF from working

MAF is nothing more than a heated wire in the glass tube, it only samples about 10% of the air flowing into the engine, so being off a little makes a BIG difference on computers air flow calculations, i.e. if MAF is off by 1% that's a 10% difference overall, 2% = 20%, ect.............

The air flow past the heated wire cools it down, how fast it cools determines the WEIGHT of the air flowing past it
Air:fuel Ratios are WEIGHT ratios, not volume
A cubic foot of air weighs more at sea level than at 3,000ft elevation, "thinner air" the higher you go
Cold air weighs more than warm air, i.e. "hot air rises", why?...................because it is lighter than cooler air
Gasoline ratio is 14.7 to 1
14.7 POUNDS of air to 1 POUND of gasoline
14.7 grams of air to 1 gram of gasoline

Gasoline's weight doesn't change much by temp

Computer already "knows" it is running a 4 LITER engine, so it "knows" engine will pull in 4 LITERS of air at Wide Open Throttle every 2 RPM, so it can calculate Volume of air at any RPM and throttle position, thats just straight math.
But it doesn't know how much a LITER of air weighs at every elevation and air temp
MAF sensor determines the WEIGHT of the in coming air, and there is also an air temp sensor as well, IAT sensor

So if MAF sensor is dirty or coated with residue it does cool down as fast as it should, so computer "thinks" air is lighter/less than it actually is, so calculated Mix is off
So computer has to add more gasoline than calculated, and that can set Lean Codes, also causes pinging/knocking

Got the labor knock as well. I'll get these other suggestions done asap. Thanks! I'll let you know what I find.

Where is that o2 sensor fuse located? My 93 4.0 won’t idle
 

Where is that o2 sensor fuse located?

Welcome to the forum

O2 sensor part generates it's own voltage, but they do each have a Heater inside, in 1993 Cab Fuse Box fuse #18, 15amp, is for the O2 heaters

O2 sensors are not used by the computer at idle or WOT(wide open throttle)