Stats: 2005 Dakota SLT, 4.7L V8, 4x4, automatic transmission, 73K miles

History: Last month I had to repair a leaking exhaust manifold and I had the battery disconnected while I did this. After fixing the problem I test drove the truck and it ran great (albiet much quieter).

A few days later when I drove the truck again it developed a very erratic idle at stop lights and actually stalled a few times. The engine threw a code but it went away before I could hook it up to a code reader. It ran like this the next couple of times I drove it but then the truck was parked for a few days and after that the idle was back to normal. (To note, it has idled rough like this one or two times in the past but never this bad and never consecutively.)

Current problem: Now the truck idles fine at the light but when I hit the gas the truck pauses or lurches forward for a second before taking off. This only happens if I come to a complete stop and the truck idles for a few seconds.

I cleaned the throttle body again (I cleaned it at 70K) but wonder if my throttle position sensor or idle air control valve are malfunctioning.

Anybody experience similiar symptoms? Thoughts?

 

If your check engine light pops up, and if the light goes off, the code will still be there as a stored code unless you reset the pcm by I plugging battery or you manually deleted it via a scanner. It should still be there. It sounds like you have a misfire perhaps since you said it has a problem taking off as well occasionaly. The idle control valve could cause that at a stop light as that valve is designed to make your engine run better at idle, which you are idling at a stop light.

 

Go to autozone or somewhere and have it scanned for the code. You need that as a starting point otherwise your shooting in the dark.

 

Spark plugs?

 

Ran the codes today: P0068 Dodge - Manifold Absolute Pressure/Mass Air Flow Sensor - Throttle Position Correlation

Possible causes
- Faulty Mass Air Flow (MAF) sensor
- Large vacuum leak
- Leaking air duct system
- Mass Air Flow (MAF) poor electrcial connection
- Manifold Absolute Pressure (MAP) poor electrcial connection
- Faulty Manifold Absolute Pressure (MAP) sensor
- TP sensor not seated properly
- Faulty Throttle Position (TP) sensor

I don't hear any whistling in the engine bay so I don't think there's a large vacuum leak. I could try replacing sensors but then I'm just guessing.

Has anybody had this code? I checked the forums and it doesn't sound like this is an easy diagnosis and fix.

Why would this happen right after replacing my exhaust manifold gaskets? Could the increased back pressure screw up a sensor?

Thoughts?

 

You can have a vacuum leak without a whistling noise. Easy think to do is check all the lines from the pcv, to the throttle body, to the air box and whatever else is connected VIA vacuum. Maybe your MAF sensor is dirty. Only clean with Mass AIr Flow cleaner only. Don't use a qtip either.

 

Seeing that 2 of the "possibles" are "poor electrical connection" I would unplug and reconnect the MAF, the MAP and the TP sensor, with the engine off. Do it 4 or 5 times each. This will "wipe" the contacts on the connections. While you have the connections apart, eyeball them to see if there is any evidence of corrosion or discoloration. If there is evidence of corosion or discolouration you may want to spray them with contact cleaner.

 

And make sure to unplug the battery while you mess with the MAF sensor. Then plug it back in after you're done cleaning it.

 

Our trucks do not have a MAF sensor. MAP and TPS, yes. I would check those out. My guess, with lurching and pausing, would be the TPS sensor.

 

Isn't a map sensor the same as a MAF? both are between the intake and the air filter.