My 99 Navigator is doing the hucka buck when I take off but if I accelerate harder it goes away, then sometimes when I get to 50 and hold it will do it again until i press pedal harder. Finally if I get to 70 and hold it will sometimes do the same thing but if I accelerate more it seem to push past the point.

Funny thing is it doesn't do this every time but as of lately has gotten worse and now CEL is on reading P0442.

I check for vaccum leaks but have not notice any and grab some carb cleaner to spray around vaccum lines and no change in Idle. Sometime I can crack up and it drives fine. The next time it does the listed things above.

I read how the MAF could cause this issue and will be cleaning it tomorrow. Any other suggestion are greatly appreciated.

 

Your drivability issue is unrelated to the DTC you've pulled.

You've most like got a misfire but it will require more competent test equipment beyond a basic code reader to diagnose.

 

These symptoms point to a failing fuel injector. Which one is the million dollar question. For that you'll either have to wait until it fails completely, or get your hands on more advanced testing equipment.

 

Thanks for the suggestions, cleaning the MAF did absolutely nothing as you guys previous inidicated. I did try changing an ignition coil or 2 but that didn't make a difference as well. Guess I will have to take it for deeper diagnostic and see what comes about.

Its still drive fine and strong one time, then the next trip its stumbles upon excelleration and sometime at the redlight, I can feel it jumping or almost skipping.

 

I just finished reading your first posts and you have been having these problems for almost 2 years now and you said the problem started AFTER the new sound system was installed. I suggest that you remove the new system and inspect the job that was done.
I think the installer did something to the wiring in that area that's causing all your problems. He may have some loose wires making contact where it shouldn't or grounding out. Inspect the area and take some pics and post them here.
I think that by now I would have invested in a gallon of gas and a match and ended the problem.

 

Um, are you reading the same thread that I am?

 

He's only made 10 posts so far. Go to all his posts and read the first one. This saga started in Jan. of '10.

 

I'll take a SWAG at this problem. I suspect that your Canister Vent Valve (part of the EVAP Syatem) does not consistantly close all the way when comanded to do so by the PCM. If it closes all the way, everything is cool and your ride runs fine. Next time the PCM runs the EVAP monitor, if the Vent valve sticks partially open, it effectively creates a small vacuum leak.

When your are at light throttle, the small vacuum leak has a large effect compared to the reduced amount of air being injested through the throttle body into the intake. So the engine goes leaner than what the O2 sensor & injectors can compensate for. That is causing the engine to buck and jerk.

If you accelerate harder, the intake is injesting a much larger volumn of air through the throttle body and the small vacuum leak has a minimal effect in comparison. The O2 sensor & injector flow can make up the difference and life is good.

When the PCM runs the EVAP monitor and the Vent valve is stuck partially open, the EVAP monitor interprets the small vacuum leak as a vapor leak in the fuel tank. In other words, the EVAP monitor can't draw or hold a vacuum on the fuel tank because of the partially open vent valve. So it throws the P0442 code.

I'd try disconnecting the vacuum line to the EVAP Purge Valve and plug the disconnected line. (That will keep the EVAP monitor from running, which will throw a code, but it will also take the vent valve out of the equation.) Then drive the vehicle under the same condictions and see if the hucka buck goes away.

If it does, you know you have an issue with the vapor return side of the EVAP System.