Normal idle speed while stopped in gear?

I've only had my truck a week, but I notice when I stop at a red light, sometimes the rpm will drop down as low as 500, but will eventually come back up to about 700 (especially when a/c is on). It's not low enough to stumble, but that still seems pretty low to me. Is that normal for these 4.0 V6's?

 

mine hangs out around 700ish rpms, never noticed any drop. when was the last time you cleaned your MAF and throttle body? or when was the last time you ran some seafoam in the tank?

 

That's exactly what my 06 DCSB does, also 4.0L.

 

I just bought it a week ago. It does have the K&N intake and JBA headers, but I wouldn't think that would make a difference. I think I do have some MAF cleaner, so I'll do that tomorrow, and I do have a bottle of Techron I haven't put in yet.

Today was the first time I've really done anything to it, I changed the coolant and radiator hoses.

 

The idle speed in neutral with the AC off should be 650 to 750 rpm:



But do not rely on the dash tachometer to accurately indicate engine speed at idle--or for that matter highly accurately at any engine speed--check it with a scantool or some other diagnostic tachometer. Idle speed is controlled by the ECU as described below; if it is not within acceptable limits a DTC will be thrown and the MIL will illuminate.



My '09 sometimes shows idle speed of 500 rpm or so, but because dash tachs are not that accurate, especially at the very low end of the scale I do not let it bother me--if the engine is running smoothly then all is well, the ECU will let you know if something is wrong...

 

I get a consistent 720 RPM on my ScanGaugeII.

 

Seems perfectly fine while in park or neutral. I've only noticed it while in drive, like when I stop at a red light, it'll drop down to about 500, then after a couple of seconds it'll come back up to 700.

It's no big deal really, I was just curious if they all behave that way. Or maybe it's just more noticeable on mine since I have an aftermarket exhaust.

 

I had this exact same issue with mine, Actually cleaned my MAF and Throttle body this weekend and now its idling in "D" @ 700ish RPM. I bought this Seafoam Spray that was recommended by my brother for the throttle body and used CRC MAF Cleaner for the MAF sensor. Runs smooth as butter now, idle was a little rough.