Hello,
Been searching rough idle threads, and have not been able to narrow it down so far.

So first of all, I have had this problem for roughly six months now, perhaps longer, however it is getting to be really bad lately.

When idling, whether it is cold or hot, (although it is usually worse when hot) Engine idles very rough, at about 700-800 rpms or so. The whole truck shakes, Even the bed looks like it is going to fall off. Never dies when doing this.

Reason I have neglected this so long, is lack of time, and money to throw parts at it. I have been hoping whatever is bad/going bad, would eventually throw some sort of code.

Only code is shows, is occasionally, a MAF out of range code.

However, when I unplug the maf, putting the computer in default, Engine runs the same, sometimes worse, and it sometimes stalls in this mode.

I have unplugged IAC, throttle position sensor, and air temp sensor and running condition shows no change,

I have not yet unplugged O2 sensors yet, because those plugs are such a pain to get to, and whenever I think of it, the engine is too hot to mess with the o2 plugs.

Plugs and wires have been changed.

Air filter fine.

No obvious vaccumm leaks.

Engine runs great at cruising speed, and basically any rpm above 1000.

Engine currently has 247xxx miles on it.


Hopefully someone can help me narrow this problem down. Like I said I haven't messed with it much, been too busy, but right now I have too many possibilities, and to eliminate some of them requires throwing parts at it.

Possibly injectors, coil? Weird leak somewhere?

 

From what I've been reading lately you could possibly have bad intake gaskets? there known for rough idle and coolant leaking when they go bad. Have you noticed any leaks? You could also possibly have a cracked head. Common on the OHVs. But I'm not certain if you say it runs great when cruising.

 

When the lower intake gasket fails I wouldn't call it a leak, more like a waterfall of coolant. Doesn't mean the upper isn't loose. Take a 13mm deep socket and snug the upper intake down. Its a small torque spec so need to pull a he man. If the idle improves I would replace the gaskets.

The heads are known for cracking between the valves leaking coolant, good news I guess is the truck burns it and mostly stays out of the oil. Check your coolant level otherwise it sounds like a rather large vacuum leak to me.

 

2 weeks now, and truck is getting worse. I have not been able to locate any vacuum leaks or isolate any sensors that may be causing it. intake gaskets are relativity new, Just pulled upper intake and no leaks that I can see. Still runs good at cruising speed so its got me baffled.

 

Did you do the lower intake to the fuel rail gasket?

 

After some messing around, Noticed that engine runs exactly the same whether left rear cyl spark plug wire is plug in or not,

But unplugging any other spark plug wire results in more shaking. Took the spark plug out, Ceramic insulator was chipped and spark plug looked lean. Changed spark plug, No difference,

Injector was ticking, but after removing it, end of it looks like it was half plugged, So at this point I thought I had narrowed it down, so I replaced it. Still no difference. Engine runs as rough and shows no difference whether the cyl plug is firing or not.

Checked compression, 120 psi according to my tester. So now I really dont know what to do with it.

 

Don't just unplug and replug in stuff.
Clean it up or replace it. unplugging it won't do a whole lot.
Clean your IAC. Then your MAF. start there. Check your wires and plugs next. then coil.

 

from my experience, no sensor plugged in is better than a bad sensor plugged in, I realize this doesnt apply to some sensors.

 

Correct. I.E. IAC if its dirtier than a sailors mouth.

 

I will Take that off and clean it tommorow. Cant hurt!!!

During messing with it today, I found a wire disconnected on the o2 harness, (butt connector crimp failed, Had to replace the o2 plug a while back ) replaced the broken spark plug and nasty injector,
Now unplugging the MAF airflow cuts down the roughness significantly, when earlier today doing so, didnt change too much, originally leading me to think that MAF wasnt causing problem.


Running it now with the MAF unplugged, on default fuel map, it doesn't run much rougher than it did when it was running normal before. Not shaking the truck bed off like it has been.

So maybe it was a combination of things with the MAF sensor.

 

You may be correct. have you cleaned the MAF? i'm not sure cleaning it at this point will save it, but it can't hurt.

 

Going to try cleaning it. Probably going to get a new one regardless, its not that expensive, ends up being 40 bucks after core and advances online discount, but 140 down intially is getting me.

 

Have a 94 ford ranger XLT 4.0lL Extended Cab. Having rough idle and occasional stalling. Usually at idol but lately is happening at driving speed also. Used to run perfect. Then one day CEL comes on and it starts running rough and trying to stall like something is clogging the fuel. Then while driving would jerk like it had cleared the fuel line andl light would go out and run perfect again. Couldn't figure what was causing this. Changed Oil, plugs, Fuel filter was changed and injectors cleaned by shop and a new fuel filter. last year but does not have but 5000 miles since installed. As time passed the light staying on became longer and times it ran perfect where shorter. Now Light stays on all the time. Have to drive with 2 feet. Always started without problems. Now I am getting occasional back fire and Black inside tail pipe. Is it possible for the ICA to be the culprit. Could it clog and unclog and clog and unclog till it stays that way or when it clogs once it stays that way. Or perhaps a loose or corroded electrical connector, Clogged exhaust system? PCM was replaced about 6 months before these issues started a year ago. So I don't believe this to be the issue. My OBD1 is broken so I have no codes yet. Need to get a new one on payday. I have no formal automotive training. I have an IQ of 147, Usually very good at figuring out problems and fixing them on almost anything. Computers, laptops, video game consoles, Arcade Game Machines, slot machines, tv's, Furnaces, Home A/C units, Etc. etc. I am self taught in everything. But this is driving me up a wall. Cannot figure what would cause it to run perfect then messed up then perfect. Any one that can help me on this I can help you with advice on fixing some of the above mentioned items. Thanks in advance to anyone that can help.

 

so to keep your MAF sensor from getting really nasty is to take your crankcase hose from the oil filler neck and put on a breather filter and that will help it out and keep your intake a little more cleaner as well