97 XLT 5.0 idling issues.

[617ricky]

So I currently own said Explorer [155K mi], and have for the past few yrs.. I've always been on top of maintenance - oil changes, tune ups, tires, etc.. But I just noticed a problem in the past couple months.. When you start it up and it's idling, the engine very gently revs every couple seconds.. I can't say for sure how many rpm's the change is, cuz the tach doesn't work currently, but I'd guess it goes up maybe 200-300 rpm each time briefly, and then comes back down.. It reminds me of a heartbeat, with the cyclical up and down..

So, can anyone take a stab at what this problem may be? It's always passed emissions every year (which are strict in Mass), so it's not like it's been running crappy for a while.. And there's no stalling issues, and the engine still has power and pickup when required.. What do ya think?

 

[Turdle]

Sounds like a slow 02 sensor during open loop warm up. If the truck idles steady when warm ( or after about 1 minute after warm start) this would further confirm this. If so no biggie.

You might also try cleaning the IAC valve

 

[617ricky]

It doesn't really subside after warming up, maybe a little bit.. I wonder if the cold has anything to do with it, cuz it's only been happening for the past couple months and I'm in New England.. Then again, that could have nothing to do with it.. It's not like an alarming thing when you hear it, but it was just tuned up ~6 months ago, so I can't attribute it to that..

EDIT: I actually just went out and really paid attention to it, and after driving it, it idles normally.. So it probably is just something minor, and possibly even attributable to the cold temps - so that's relieving..