RPMs up and down at idle

[S550ilver]

After washing the car yesterday, I moved it over to get my other truck in the garage. While doing this, the RPMs started going up, then down, up down...maybe 500 RPM, maybe a bit less. THis has never happened before. I tapped the throttle and the pulsating stopped...sat out there for another 20 minutes and it never happened again. Even later in the evening went out and started to see if it would happen again. Nothing out of the ordinary. I didnt wash the engine, just a usual wipedown with a waffle towel. nothing came unplugged or anything while drying...Figured this may be one of those "glichy" once in a bluemoon things. Anyone have this happen?

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[Boggus]

Mine does it sometimes, usually with the AC on at cold startup.

 

[Chameleon]

Try blowing on the the MAF sensor and make sure the stock air box is tight.

 

[S550ilver]

Ill check the airbox tonight and make sure nothing came undone from the wipedown. And the A/C was on and it was a cold start....I appreciate the responses.

 

[BmacIL]

Happens sometimes on cold start with A/C on. It's normal (if not a little odd).

 

[jasonstang]

If it's AC it shouldnt be that much rpm change. 100-200 max.
My auto on the other hand idles louder when ac kicks on.

 

[garbancillo]

Mine does it sometimes, usually with the AC on at cold startup.

Mine does it also since i picked her up from the dealer, but only when I switch on the AC with the engine well warmed up previously, never in cold starts. They told it could be considered as normal.The ECU would "learn" as the time goes by that it should order the engine to rev up just a liitle bit at the time the AC is switched on to attend a peak of higher demand caused by the AC compressor being put on service.

The trouble is that after 8 months, the ECU has not "learned" anything at all, whilst other Ponys were already "well learned" on leaving the assembly plant... :tsk:

Yuk!

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