99 4.6L missing and rough idle HELP!!

[gothamknight]

I have a 99 4.6L w/ 130K miles. I recently did a complete tune-up w/ new PCV, fuel filter, plugs, wires. It had been running on the originals until that point. I have had no problems with the truck until about 6 months prior to doing the tune-up. At that time I started noticing a hesitation or miss under a light load, mainly when lightly accelerating at highway speeds. Also the truck began to have troubles at startup. It would act like it was going to stall for about a minute before settling down. It also does not idle as smooth as it used to. I was hoping that the tune-up would take care of the problem. The problem continued. I have since replaced the MAF sensor. The problem seems to be a little better but it is still having the same problems. I have read that the ICV?? might be the problem. Anybody that has suggestions would be greatly appreciated. Thanks

 

[gothamknight]

I am also wondering if I have a bad EGR valve. Is it hard to replace? How much will it cost me? Does anybody know of a link that walks you through the process? Thanks again

 

[Ugly John]

You may have a buildup in the throttle body off the EGR valve. I replaced both the sensor and the valve, with the same hesitation still occuring (I did have the check engine light come on though). I removed the throttle body, and cleaned a mess of junk that was off the port. No more problems after that.

The 4.6 is notorious for this problem.

 

[Alaska Mike]

I'm having the same problem with my 99 5.4litre (61,000 miles). I recently had the check engine light come on and the problem was diagnosed as the #4 cylinder coil pack. I replaced the coil and the misfiring went away. Now, a couple of weeks later, we are experiencing the shuddering/lack of power while under a slight load. Is this the same problem with the throttle body?

Alaska Mike

 

[frank4.6EB992WD]

i also have a 99 4.6 EB with about 75,000 miles, no problems except a couple months ago check engine light came on and had trouble starting in the morning, took it to a mechanic he diagnosed it and he said the oxygen sensor was bad he put a new one on and had no problems ever since.

 

[Alaska Mike]

Update:

I ended up changing plug on the cylinder with the bad COP and replaced the fuel filter as well. My power-loss problem went away. Not sure which fixed it, but the plug needed to be replaced and the gas that poured out from the filter's intake side was filthy.

Alaska Mike

 

[pcrider]

I got a similar rough idling with my 02 XP mechanic said it could be due to the aftermarket exhaust installed since it was just tuned up less than 1000 miles back.

 

[kaoshen]

Hey GOTHAMKNIGHT did you ever figure out what that problem was? I have the same exact problem with my 98 Expedition 5.4L and my mechanic is not sure what it is. He did suggest a minor tune-up (plugs and fuel filter) before changing the coil packs($60.00 each). Let me know thanks!!

 

[Porkchop]

I had the same problem as well, however it turned out to be something totally different than anything listed here.

Oddly enough I am having a problem with oil getting down into the plug area. It is causing the plugs & wires to misfire. It seems to be a reoccuring problem. I was told that on the 5.4 aluminum head engines that it is oil seeping through the pores of the metal.

Mine is a 4.6 and I believe they are cast iron heads, I'm not sure. Haven't even looked close enough to it yet to tell what it has.

You guys might wanna check that though.

 

[nancielovesmark]

What a coincidence....

I also have a 2000 XLT w/4.6, and was plagued with the same problem. I had the check engine light come on, so I took it to the local "trusted" mechanic. He ran the codes and it came up that my #1 cylinder was misfiring. We changed the coil pack, and that helped for about 10 minutes. Next, he thoroughly cleaned out the EGR Valve and determined that I needed a new one. So we replaced that. The check engine light was reset, and off I went. Ran great.........so I thought.

Two months down the road, my Expy started misfiring again. So back to the "trusted" mechanic I went. This time they read the codes and said that the #6 cylinder was misfiring. So we replaced the coil pack there, reset the check engine light and off I went again. Ran great...............for about 2 miles. I immediately drove it back to the mechanic and he quoted me $1000 to replace the other 6 coil packs, that he stated, "would go bad one after the other". I just about sh*t myself. I asked for my keys and left the premises with a poorly running vehicle that I had already spent nearly $1000 to fix just two coil packs and an EGR Valve. I went to the local auto parts store, spent $400 got the rest of the coil packs and changed them myself. Turns out that you only have to unscrew 1 screw and unplug one plug to get them off and then repeat the process backwards to install the new one. Takes about a minute and a half to do, and I was being charged $180 labor for each one. I guess I am in the wrong business. I would love to make $180 every minute and a half!

Due to this scary experience with a "trusted" mechanic, I prefer to read manuals and do it myself or take it to a dealership (and sometimes you can't trust them either). It is apparent that this is a common problem.

So far so good, I haven't had any more issues since this and I just recently upgraded my exhaust system to a Flowmaster 50? series. It has a nice low rumble at idle and deep throaty sound under load. I love it and it may have increased my gas mileage by one or two gallons too.

Good luck with your Expy!