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Traffic Jam Malfunctions

I have a 2003 Taurus, with about 120,000 miles. For the most part, it runs pretty well, getting the same gas mileage it did 3 years and 80,000 miles ago, when I bought it. However, recently, I have noticed that when I’m stuck in a traffic jam for an extended period of time, with the engine just idling (letting the idle pull the car forward the 3 feet I managed to go in the last 10 minutes), the engine begins to run rough, with a knocking sound, and feels as if it is going to stall. Then if I step on the gas, the engine does not “rev” up right away; there is a very distinct hesitation (as in several seconds). Apart from never getting in traffic jams, what can I do about this?

I suspect there’s more to this, some things you haven’t mentioned. Does the check engine light come on? Does the temperature creep up into the red zone? Anything else you’ve noticed?

You may be experiencing pre-ignition. This can happen when hot spots develop inside the cylinder. Hot spots can be areas where carbon has built up, hot valves, or the like that get so hot they can ignite the gas mixture before the sparkplug does. The mixture explodes at the wrong time, as if the timing was off. This can create the symptoms that you are experiencing and explains why it only happens when the engine is subject to being overheated.

No, there are no other noticeable signs. I made a point of ensuring the temperature gauge was OK (assuming it works, of course!), there is sufficient gasoline, the check engine light is not on (or any other “idiot” lights, for that matter."

So what, if anything, can I do about that? Does it suggest a larger underlying, or future problem?

The knock, when sitting in traffic, could be the engine getting hot, and the fuel/air mixture getting lean. When the engine is cool, open the radiator cap and make sure the coolant is to the top.

Do you hear the radiator fan(s) kick on when in traffic? If they don’t, the engine may not be hot enough; or, it may be, but the engine coolant temperature sensor isn’t telling the engine that it is hot enough. Does the radiator fan come on when you turn the A/C ON?

Check the fuel pressure in idle. Is that the original fuel filter?
The engine could be missing from erratic spark; but, that’s trickier to hunt down. A crankshaft position sensor (cps) getting hot and reading wrong, is a possibility.