Engine runs very rough when sitting in traffic and
Engine runs very rough sometimes, not only when sitting in traffic, but also at times when travelling down the highway, with my foot on the gas. It acts like it's going to die, but hasn't .....yet....then the AC blows hot air. The check engine light comes on and then goes off for a period of several days sometimes, but then comes back on. It also seems like there are power problems. Sometimes when taking off on a hill, I am pressing on the gas, and the RPM's are going up, but it is very slow to respond.
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I had a similar problem on a 2004 Jeep Grand Cherokee V8 engine.
Nothing seemed out of the ordinary except that occasionally the engine would run rough. Another seemingly unrelated symptom was that when shifting out of Park the transmission would sometimes jolt.
Turns out that I had a bearing on the serpentine belt tensioner that was freezing up. My belt broke and while I was changing the belt the pully on the tensioner fell into my hand. The bearing had seized and the plastic hub had disintegrated. After getting the new tensioner and belt. I noticed that the rough engine and the hard shifting transmission problems have gone away.
Seems that the engine was having to work harder to overcome the bad bearing.
Another cause of rough engines comes from dirty fuel injectors. The best solution I have run across is Chevron's Techron fuel additive. I had a honda Prelude that had a rough running engine. The Honda technician advised me to start adding Techron when I fill up. Worked like a charm. After the second tank I had no more problems. I have tried other fuel additives over the years, but Techron seems to be the best.
Also be sure to change your fuel filter. A dirty fuel filter will cause a noticeable drop in power.
Are your rpm's low when sitting at a stop light and vehicle warmed up? You could check your TPS (Throttle position sensor) or maybe your egr is plugging up, or one of your plugs or wires could have gone bad, maybe the coil on one of the wires is bad. You really need to plug a code reader into the ECU and see if there is a code being thrown. And NO, all codes will not cause the engine light to come on.
A properly-operating engine should run smoothly and without excess noise. If your engine starts operating in a manner that gives you the perception of "running rough", it is likely due to a handful of common causes. A mechanic would investigate these common causes first in order to rule out a simple explanation for the engine's unsatisfactory operation.
The common causes for rough running in an engine are:
If it has a problem bad enough to stall, it should record something on the computer. Autozone or Oreillys will scan for free. You should have a circuit or sensor to speed up the idle or at least turn on a cooling fan to bring down the engine temperature.
Some of the DOHC engines use a part called a "Cam Phaser" to adjust the variable cam timing. You may want to have the Dealer run your VIN for a Recall. Ford was extending the Years and Mileage coverage and it can be a $2400 repair. If you hear a "tapping" noise that disappears after 2000RPM, thats another symptom.
I don't know the model year? Key on engine off, use a gage and check proper fuel pressure. Then with key off, see if pressure holds for a bit? If it drops like a rock, check for a fuel pressure leak. If the engine is hot and trying to flood for some reason, your going to have a tough time. Any applicable trouble codes? Check your coolant temp sensor, only if testing leads in that direction.
Smell of your crankcase oil dipstick, does it smell like gas?