I have an 08 mega cab with a 5.7 hemi. My problem is when I start it cold it revs up to 1500 rpm and takes about a minute and a half to idle down after that you can shut the truck off and restart it and it will do the same thing until warmed up. You can also shift it while still at the higher rpms (which i dont like to do) and go back to neutral or park and the rpms are low, but if you turn the engine off and restart the same problem until the engine is warm. I took it to the dealer because it is still under factory warranty and they said there were no computer or sensor problems and blame it on ethanol and varnish build up on the throttle plates. They recommend cleaning the fuel rails, throttle plates and air intake system for $230. I have cleaned the mass air flow sensor and throttle plate my self but that did not help. Does anyone have any ideas.

 

i don't know about 1500, but a higher idle is normal when the negine is not warm.

 

You should find another dealer for your service. All engines should "high" idle while cold. Although the Hemi is notorious for gunk build up on the throttle body, it should not be necessary on an '08 yet, it should be a once a year routine to clean it...

 

Higher RPMs are the result of fuel injection. Fuel injection does not have a "choke" like a carb does, so to compensate, it will run higher RPMs until warm. It will also increase the RPMs even higher when there is a load on the motor (in gear). This is normal, my 08 QC 4.7 w/ 6spd does the same. Hopes this helps. just my .02

 

You want a higher idle for warm-up. Even our old farm pickups that have carburetors have a high idle position and when we leave with them, we hit the gas pedal to "knock it down."

 

I believe that is normal with the Hemi (1500). Mine has done it from day 1 regardless of engine temp. I will read up on it again as I know it says something in the owners manual about this. I believe it also states that putting the transmission in any forward gear before the engine reaches normal idle rpm could damage the transmission. By the way, I'm assuming your truck has the 545 RFE Transmission. Mine does !

 

Like hammer said take it to another dealer in the future...they're trying to squeeze unnecessary money out of you. They know it's 100% normal and I guarantee they would just charge you the $230 and not even touch your truck because it doesn't need it.

Oh and the hemi is speed density so there's no MAF...you're probably thinking of the little IAT sensor. It doesn;t need to be cleaned but the throttle blade does once in awhile.

 

It very well could be normal, I was use to my 05 hemi that started up high and went back down almost instantly. I figured the dealer was probably trying to get something out of me, but im leary of what they tell me.

The throttle blade was a little gunky behind it, the front side was clean. The dealer might have cleaned it though. The thing I thought was the air flow sensor was mounted in the air resonator. Is that the IAT? What does that stand for?

I'm thinking about checking into an extended warranty just in case something major happens. Do you think they are worth it. I bought the truck used and not sure what all was done to it before I got it, but I know some mods were done to it like the exhaust and I would like to do more so it might not be good to get one.

 

Intake air temp. My 08 idles up for a bit when cold too. Normal to do so for emissions reasons. It warms the engine faster because these Hemi's warm up slow compared to my old 01 5.4L Ford. It had heat in about 2 miles. The Hemi takes closer to 10.

 

My '08 4.7 does the same thing.....it settles down in about 2 minutes or so...