I recently got a 2000 dodge ram 1500 sport 4x4 and I noticed it has a rough idle. It'll move up and down about 100rpms and doesn't ever settle. I assumed it was because one of the injector wires were completely cut but I got it fixed temporarily and it still does it. I checked for vacuum leaks and found none. It does have a straight pipe and is missing a downstream 02 sensor but even when I clear the codes it'll idle rough way before the code ever comes back. Interesting enough I found if I pump the brake pedal it'll slightly raise the rpm's then drop really low, 200-400 rpms, and will sometimes die; this leads me to think there is still some vacuum issue. I was told it "probably" had a plenum repair, but I checked the plenum plate with my magnet and it does indeed still have a steel plenum plate, so if it does, it wasn't done properly.

 

The plenum issue is a combination of cheap gaskets, and bolts that were too long. The whole "dissimilar metals" thing just doesn't fly, as the difference in movement is measured in ten-thousandths of an inch...... Shorter bolts, and a GOOD quality gasket solves the problem permanently.

Unstable idle is indeed likely a vacuum leak. Does the engine idle rough right away? Or will it run smooth for a couple minutes, and then start freaking out?

 

Yeah I’m pretty familiar with the plenum repair. I replaced the plenum on my 94 dodge from Hughes engines. Yeah it idles rough right away. Also I should mention it has a hard time starting sometimes and also you can hear a hissing (sounds like a plenum to me)

 

Check fuel pressure. See what that looks like. How old/what type of plugs in there? Last time cap/rotor was changed??

 

Will check fuel pressure soon. To my knowledge the plugs were changed last year, however the person I got it from said it needs a tune up. I got a full tune up kit and planning on installing that this weekend. Also I checked for a plenum leak by disconnecting the PCV and flipping over the oil cap and it appeared to had no vacuum leak. However once I reconnected the PCV hose, the truck died

 

That should tell me something, but, I seem to be stupid at the moment..... (getting on toward bedtime. Sucks bein' old. )

Make sure you install good ol' copper spark plugs, these trucks don't like the rare-earth fellers.

 

Under the heading of...it couldn't hurt...try removing every vacuum hose from the keggar and plug them so no air can be sucked thru them. Try your beast that way n see if there's any difference. Also, what are your long and short fuel trims...idle/1500/2500 RPM and the intake air temp? Do this test in your driveway, not on the road.

 

Yeah I know that's how you're supposed to do it but I didn't plug them off when I tested it but I'll give it a shot. Unfortunately I can't see my long/short term fuel trims as the obd - II port is broken so I can't put my scanner on it, unless there is someway I can check otherwise. By chance would you know what my fuel pressure should be once I test that?

 

Minimum I believe is 40 psi but would be closer to 45

 

Fuel pressure should be around 49 PSI at idle.