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Ford Ranger Stalling Problems

My beloved standard, 2000 Ford Ranger, with an estimated 170,000 miles on it, has a problem with stalling that keeps getting worse.
2 different garages have failed to fix this problem three times. Many parts have been replaced/checked (like battery, plugs/wires) and the fuel and induction system was cleaned, fuel pressure, Compression and engine vacuum were all fine. The Check Engine Light goes on and off all the time and does not seem to relate to the problem. When the last garage hooked it up to the computer, nothing related to the problem was identified, they reported. The invoice/report from them is attached to this posting.

My problem began about 2 years ago. The truck would only stall out when I first began driving, after about a mile, and only if I was going downhill and was coming to a stop. Then it would putter and choke and ultimately stall out completely. After my 30 minute commute (near highway speeds) the truck would then be fine the rest of the day, with no problems stalling when I drove to a meeting or out to lunch. Since it began, it has gotten steadily worse. Now, pretty much whenever I decelerate downhill, and come to a halt, it will stall out unless I leave it in neutral and keep fluttering the gas peddle to give it more gas. It even happens when I’m not going downhill. It does not happen when I first start driving, but after a mile or so, it happens almost whenver I come to a stop. It sounds like the truck isn’t getting enough gas, and if I don’t keep pumping it with signifcantly more gas, it will stall.

Once stalled out, if I try to start it up again immediately, it is VERY hard to make it start. I have to keep turning it over before it finally sparks to life. It sounds pretty awful. otherwise it starts easily. IF, however, I let it stall out in a parking lot at a gas station, for example, and I go into the store and make a couple quick purchases, when I go out to start the truck, it fires right up with no problem. It only has a VERY hard time starting up when I’m in an intersection and try to re-start it immediately after it stalls out.

The two different garages that have failed to fix it were both able to easily replicate the problem, so that was not an issue. Amount of gas in the truck and temperature outside are both irrelevant.

My username is accurate: I’m not mechanically inclined at all, I’m ashamed to admit. But I keep hoping/assuming that my detailed description of the behavior will enable craftier folks that me to diagnose it. Thank you.

It sounds like this is always an off the gas pedal problem?

When you feather the gas pedal you’re not giving it more gas. You’re giving it more air. (The computer decides on the gas depending on other conditions - like how much air it thinks you’re giving). When you are off throttle air control is done with an idle air control (IAC) valve. This would be the first thing I’d look at.

Do not assume that the error codes that come w/ the check engine light are unrelated no matter what anyone told you. Find out exactly what the error codes are/were and post them. (Format: “P1234” - many auto parts stores will read them for free if your engine light is on).

Billed for 8 plugs so I’ll guess its a six not that it matters much. You should be able to unplug the IAC (9F715) with the engine warm and have it remain running at around 550RPM and be able to control the idle otherwise. Make sure the air intake “zip tube” isn’t cracked causing an intermittent bypassing of the MAF sensor. I’ve seen that happen a time or two. Sludgy intake plenum or an outright intake gasket leak? Check that too.

Well two items come to mind. A defective fuel pump or sticking Idle Air Control valve. The only good way to verify a defective fuel pump is to drive it with a fuel pressure gauge installed and monitor fuel pressure. I have replaced defective Idle Air Control valves, but normally that is more of a stall at idle issue. Defective fuel pumps also show up as a crank no start or crank and takes a long time to start. Always check for any vacuum leaks and make sure the air intake hose is secure.