Engine is intermittently choking up

[Marcus001]

I have a 1999 3.0L 2WD Ranger with 115k miles.

I bought the truck about a month ago, and two weeks ago it started doing this. It only does this after the truck has been driven awhile and then shut off, and it only does it at idle. When it happens, the best way I can describe it is that the engine chokes up and wants to die (it hasn't actually died yet). While it is doing this if I give it gas it takes it about a second or two to actually rev up, and when it does a lot of black exhaust comes out. Once the engine clears itself out it, it usually runs fine for a little and then repeats. Sometimes this keeps happening (every time it goes to idle), sometimes it happens once and then it is fine. The engine runs fine while I am driving around. I don't notice any loss of power, etc (idles a bit rough, might have a slight miss at idle).

So far I have replaced all of the plugs and wires and today I replaced the EGR valve. The only thing I can think to do next would be the O2 sensors, but I thought I would ask here before I go waste more money. I don't get any CEL's (they might be burnt out), and I have not read the codes yet.

Any and all thoughts or comments are appreciated. Thank you!

** Edit **

I also removed the MAF sensor and let it soak in cleaner for 12+ hours.

 

[RonD]

Well the black smoke means the O2 sensors should be replaced after you find the problem, not before though.
Black soot coats the O2s and causes them to misread oxygen in exhaust.
O2 sensors 'fine tune' the air/fuel mix, they couldn't produce the kind of rich exhaust you describe.

CEL light should come on with the key, if you don't see it light up then previous owner may have removed it or blacked it out, could be a burnt out bulb but that's more of a longshot than PO tampering, lol.
That's one of the "heads up" when buying a used car now-a-days, no CEL = no Buy
I would certainly hit an auto parts store and get the codes read for free, write them down!

Exhaust smoke reads like a sticking or leaking fuel injector.
Try the "Clear Flooded Engine" routine to test for that.

Set up engine so you will get the rough idle with black smoke, i.e. "driven awhile"
Shut off key
press the gas pedal to the floor and hold it down
Turn on key
Computer will see TPS(throttle position sensor) at the Full throttle position(foot to the floor), this tells the computer to start the "Clear Flooded Engine" routine, computer shuts off fuel injectors.
Crank engine to start, it should just crank and not fire at all, keep gas pedal to the floor, try it a few times.
As soon as you release gas pedal engine will start and computer is back in regular mode.
If it fires at all during the test then you have fuel leaking into the intake from an injector, or from the Pulse Damper(check vacuum hose at the end of the fuel injection rail)

If it doesn't fire at all then could be MAF sensor(clean it), computer bases 14:1 air:fuel mix on what the MAF tells it, if MAF is reporting more air than there really is then engine runs rich

 

[Shoddy Cologne]

it could be something like old gas or water in your tank. I'm having a similar issue with my 99 explorer

 

[Marcus001]

Well the black smoke means the O2 sensors should be replaced after you find the problem, not before though.
Black soot coats the O2s and causes them to misread oxygen in exhaust.
O2 sensors 'fine tune' the air/fuel mix, they couldn't produce the kind of rich exhaust you describe.

CEL light should come on with the key, if you don't see it light up then previous owner may have removed it or blacked it out, could be a burnt out bulb but that's more of a longshot than PO tampering, lol.
That's one of the "heads up" when buying a used car now-a-days, no CEL = no Buy
I would certainly hit an auto parts store and get the codes read for free, write them down!

Exhaust smoke reads like a sticking or leaking fuel injector.
Try the "Clear Flooded Engine" routine to test for that.

Set up engine so you will get the rough idle with black smoke, i.e. "driven awhile"
Shut off key
press the gas pedal to the floor and hold it down
Turn on key
Computer will see TPS(throttle position sensor) at the Full throttle position(foot to the floor), this tells the computer to start the "Clear Flooded Engine" routine, computer shuts off fuel injectors.
Crank engine to start, it should just crank and not fire at all, keep gas pedal to the floor, try it a few times.
As soon as you release gas pedal engine will start and computer is back in regular mode.
If it fires at all during the test then you have fuel leaking into the intake from an injector, or from the Pulse Damper(check vacuum hose at the end of the fuel injection rail)

If it doesn't fire at all then could be MAF sensor(clean it), computer bases 14:1 air:fuel mix on what the MAF tells it, if MAF is reporting more air than there really is then engine runs rich

Thanks for all of the information. I will give that a try and report back.

it could be something like old gas or water in your tank. I'm having a similar issue with my 99 explorer

One of the things I originally thought was that it had bad gas. I've ran four tanks through it so far (about half way through the fifth) and there has been no change. Thanks for the reply though!

 

[Shoddy Cologne]

dumping a can of Seafoam in there never hurts. it's worked wonders on my pickup that had a gummed up Carb, just my 2 cents.

 

[Marcus001]

dumping a can of Seafoam in there never hurts. it's worked wonders on my pickup that had a gummed up Carb, just my 2 cents.

When I bought the truck I put a can in the oil (changed the oil two days later), and a can in the gas tank. Since then, I have run four tanks of gas through it, each time putting a can of Seafoam in it. Thanks for the response!

 

[Marcus001]

Thanks for the help. Earlier today I tried that routine again, and it fired the truck up when it shouldn't have. Today it was running the worst I have seen it so far. At least I know what the problem is now! This weekend I will replace all of my injectors.

Thanks again!