Here's a similar problem but not. '98 4.6 with 300K regularly serviced. What started out as an almost undetectable shudder when accel. from stop has evolved into rythmic and non-rythmic misfire, feeling like one and several cylinders are affected. Original codes were P0401 and P0304. My Mechanic is truly a pro and is down to having to just replace parts which he and I hate to do. EGR ports were blocked and plugs and wires were due for replacement (80,000 miles). EGR system cleaned out, new plugs, wires, #4 injector, and coil pack replaced. Now P0401 but no other codes. I'm not worried about replacing the DPFE but the only thing left is what, the computer?
Additional history is several years back a rust hole in the roof allowed water to get in and affect everything from the keyless entry to visor vanity lights. Two years ago I had a dead battery and then found the radio clock lit up and the interior fan running with no keys in the car. Those infrequent symptoms wen away a while ago but when wet again, the air spring compressor would come on every minute and some buzzing noises to the left of the steering column would subside when I turned on the windshield wipers. The visor vanity lights and map light s don't work but the dome light does. I know I've got my money's worth out of this thing but it's still a good looker with pretty new Michelins, brakes, rear end, shocks, steering components, and a/c therefore another couple of hundred is nothing. A thousand is out of the question. Any ideas?

 

Possibly the GEM module on the interior stuff. I would say the DPFE is causing the code. They are known to fail.

 

Jimmy, Thanks for the GEM tip and I was thinking it would be a good idea to replace the DPFE but will either one of these things cause the engine to misfire to the point of being almost un-driveable? and now the P0304 code has returned. This 304 has been noted before but I'm sure this heavy misfire is not related to just one cylinder. Almost like the timing is changing with now an occasional "quiet" backfire. I've driven this a few miles 3 times over the last two weeks and it continues to deteriorate.

 

For those of you who've had simlar problems, mine like many are found layer by layer. I have not replaced the DPFE sensor for the 401. The biggest epiphany was determining the source of intermitent misfire (304) that would come and go. I replaced the 100k mile wires, plugs, injector, and switched coils but it took complete failure to find the culprit-fuel pump.

 

Subscribing. Only code left I need to get rid of on my son's V10. Only get to work on it every couple weeks as he is working overtime. With the replacement of vacuum hoses, cleaning MAF and new air filter, got it down to only coming in about every two weeks. I can see the problem is still there with my new AE scanner in monitor, but not bad enough to throw the code. It's been to the dealer three times over a couple years with no results. They say vacuum leak but unable to fix. Figured I couldn't do any worse. I'll be watching/working and will post back if I find it.