99 D, 5.9l - Was running rough (see other post), so I replaced spark plugs and wires, new TPS, new water pump, new fan clutch, new thermostat, new air filter, mystery oil in crank case and fuel tank, sea foam in throttle body... cleaned the hell out of this thing. (waiting till tomorrow to replace intake gasket)

(autolite plugs recommended in another thread and duralast wires, in case you want to know)

Hooked battery back up, BINGO! Purred like a kitten, sounded brand new! Let it run a few minutes, revved it up a bit (stayed under 3k rpm), all of a sudden, back to rough idle. Disconnected battery long enough for another PCM reset. BINGO! Right back where we started. Sounded great, ran like new. Ran a few minutes, right back to rough idle. (No overheating yet, thank god, but I haven't really put it through its paces yet either)

Any thoughts?

-Brad

 

Try cleaning up the o2 sensors, maybe it is leaning out a little???

 

Here's a new symptom... I decided to take it out for a test drive after the third PCM reset, and an old problem resurfaced. (it used to do this about 2 months ago, but went away)

I have a HUGE hill about 2 miles long and about a 35% grade. I roll down the windows, turn on the AC full blast, and nail it all the way up the hill.

On my way to the bottom of the hill before I turned around to go back up, I was coasting at about 55-60 mph and listening closely to the engine. Every once in a while, it feels like someone just taps the brakes for a second. I have a tiny nosedive, I lose about 300-800 rpm depending on my current speed, then it just resumes the previous speed all of a sudden. Regains about 90% of the rpms it lost, and continues on for a minute or two before doing it again. If I stay on the gas, it doesn't happen.

How about that one?

Thanks,

-Brad

 

i'd replace pre-cat o2. not worth cleaning.

loosing rpm sounds like an upshift of transmission, or tc lockup. service transmission regularly, don't worry about it, hope for the best.

 

The change in rpms could be the TPS, I would look at that before anything else.

 

if you let it run like that will it throw a code? sounds like it's going thru it's diagnostics on the reset and failing something. check for codes using the key on-off-on-off-on method (show's on the odometer) and let us know if any show up. On a pcm reset, the pcm starts going through a diagnostic/learning period... takes 300~500 miles to complete them all and several key on cycles.

welcome to df...