I'm Stumped

Hey. This is Eileen from Asheville, NC. I’ve got this 1999 Ford Ranger that is giving me trouble, as usual. I took her in b/c every now and then I’ll try and start her up, and she will start. But she won’t idle. She will just shake and turn off unless I throw it into gear and race down the road before she gets a chance to do that. Even then, she might even shake and stop and a light unless I keep her rolling. I try to park on hills and not get behind buses more often if I can. Every now and then, that won’t even work, and I have to jump start it. I thought I’d let it ride b/c it only happened every now and then. But I finally took her into the shop b/c she shook and stopped at a light and left me stranded. The mechanic changed out the spark plugs and wires, a heating cooling pump, and a fuel filter and said I was good to go. Well it’s been out of the shop for less than a week and I took it back b/c the same problem started up again. Of course they say that the truck runs great now, but its something that happens every now and then. So the mechanics are stumped and so am I. I don’t want to be stuck on the side of the road again. Please help me.

I think that the idle air bypass valve (aka IAC) would be a really good suspect here.

I completely agree. Does it help at all if you give it a little throttle while at idle?

An engine needs the right amount of air, fuel and a good spark to run smoothly. It sounds like the mechanic had little diagnostic skills and just threw some likely parts (that he knew how to change and were profitable) at the problem. In the medical profession he would be called a quack.

Your truck MAY have needed spark plugs, or a fuel filter.

If I had been in your shoes, I would have personally tried a fuel injector cleaner (cheap), changed the air filter (cheap), and if the truck had a fuel filter that was easy to change, I would have done that. That would have left poor spark plugs, or a weak fuel pump. Also, of course the Mass Air FLow (MAF) sensor would need to be checked. But that a mechanic’s job.

What is a heating/cooling pump? Did the mechanic change the water pump? You would only do this if the engine was overheating. It seems unrelated to an engine stalling. Unless it was seized up, not likely. On the other hand a seized up air conditioning compressor could cause the truck to stall. That happened to my wife’s car some years back. She simply cut the belt to get home. If that was the case, you would not have needed new spark plugs.

Of course you need a better mechanic; one who has some diagnostic skill. This one is a “parts hanger”.

Others on this board will give more detailed advice no doubt.

My vote is for the Idle Air Valve also.

Yes, it does. I just got it back and the mechanic changed the DPFE sensor. Not sure what that is. But he seemed like he wasn’t even sure if that was the problem and he wanted to satisfy me that he had actually done something. He couldn’t really explain to me why that would make my truck run. And of course it is running now, but who knows about later.

I’ll second that vote for the IAC. It’s sort of a common problem with these little trucks.

Ditto for the IAC valve. A dirty mass airflow sensor or a vacuum leak could also cause this to happen. Fords can be very sensitive to any unmetered air getting into the intake system. The IAC valve is the strongest suspect, though.

I just looked at the receipt for last time I took it in and it was the coolant temp sensor he changed, to be more specific. Would that have anything to do with it? Now they are telling me that the exhaust manifold gauge is leaking. I do have a high flow muffler in there, if that has anything to do with it.

Eileen - the part everyone is referring to, the IAC, is generally pretty easy to replace. I’m not sure where it is on the 4 cylinder Rangers, but on either of the V6s available in 1999, the part sits right on top of the engine. You literally unplug it, and then there are two bolts you remove. Neither is hard to get out, and they aren’t put in that tight (snug them down by hand and you’re good). This part will run you $25-80, depending on brand and where you buy it. If you go aftermarket, you can generally get it for $55 or less.

I don’t believe that this is a repair that you would not be capable of making yourself, and at least this is a reasonable guess if you’re throwing parts at it, based on all your symptoms. I’m frankly stunned your mechanic hasn’t tried it, as it seems like such an obvious first place to go check.

Even if you don’t want to try it yourself, I’d highly recommend finding a new mechanic.

If you do, let us know, and I’ll step you through it.

The DPFE sensor is part of the EGR (exhaust gas recirculation) system - its an emissions control system that puts some of your exhaust back into the intake with the incoming air. It reduces combustion temperatures and thus nitrogen oxide emissions. A problem in the EGR system can cause rough idle problems if the valve sticks open - its not supposed to be open at idle. BUT, the odds that a bad DPFE would cause it stay open at idle are - what? Zero?

Added to the info that holding the throttle open a bit helps still points to the idle air control valve. If a stuck EGR was a problem a little bit of throttle would probably stall it out - a lot of throttle would probably keep it running.

An IAC is normally quite easy to pull off and clean.

Ok, I’ll give it a try. Thank you