99 Ram 1500 4x4:

First issue:

After Morning cold start, runs fine for about 2 minutes, then when it drops off of fast idle it starts to have a horribly crappy idle, sounds like its going to sputter and die.... after idling crappy for about a minute it stabilizes on its own and runs normal. This issue only happens after a cold start, never happens when its warm, and only happens at idle. My truck idles at 800-900rpm cold and 600-650 warm. Basically this issue happens during the transition from fast to slow idle.


Second Issue:

Metalic grinding/rattle noise coming from engine area or possibly underneath the truck somewhere during acceleration, does not happen when cruising.

Its not very loud, its actually not even audible unless the windows are down.

Happens only in first gear, at around 2k-2500 rpm, only happens if you accelerate hard, does not happen during light acceleration.






Parts replaced / Work done:
New Plenum, New IAC, New Plugs and wires, new Cat


Please help me...Im going crazy.

 

i also have that rattling noise when on the gas. 2 mechanics a dodge dealer and my exhaust guy all see no issues. no idea at all what causes it. but its gotten a lot better over the past winter. i barely notice it now. however, before, it was horribly loud.

as for the idle, ive got that as well. but it doesnt happen every time so i ignore it. new cat, oil, tuneup etc didnt resolve it

 

For the idle problem, that is a sign of a failing pre-cat O2.

Need to isolate where the grinding is coming from..... that should be fun......

 

What makes you think its the pre-cat O2? Just curious...It would totally make my day if it was something that simple....But someone told me the new IAC would fix my issue....and it didnt =/ WOuldnt this happen all the time, instead of for a few seconds when its cold only if it was the O2?

Ill try and isolate the sound.

 

Failing sensors only completely fail about 50% of the time, it seems. The other 50% of the time they just get sloppy; they do their jobs well enough not to throw a code/CEL, but not well enough for the engine to run near perfect. The computer can "learn" around them, which may be why it fixes itself after a few minutes, but its best to replace the sensor.