Up till recently my truck idled normally at around 700 rpms, when first started up it would idle around maybe 1000 rpms then go down after a min. but now it idles around 1800 when first started and goes down to 1500 rpms after a min or two but then stays there for a long time. Even when you first start to drive it it idles like that. Any ideas....

'97 f150 4.6l

 

Sounds like your IAC is acting up. Do you have a CEL?

 

Well yes, i had my IAC off along with my TB not very long ago. They werent bad, the TB was basically the only thing that need to be cleaned. had some carbon build up. I do have a CEL and its for one of my cats but it has done it before the CEL came on.

 

You had a pending code before that took a while to become a hard code. The pending code will not set the CEL on a Ford. I would say you have a cat stopping up, but before you replace it I would have the truck checked with a scanner that will read mode 6.

 

So in other words your saying i should get a more detailed scan? You thinking the high idle could be caused by the faulty cat?

 

So in other words your saying i should get a more detailed scan? You thinking the high idle could be caused by the faulty cat?

 

When i got it scanned recently the code they pulled was the P0420 Catalyst Eff. Below Threshold.

 

I would be more than 95% sure you have a stopped up cat, but I would look at the readings on the last O2 sensor and its wiring. A cat is not cheap.

 

Also, buy a Ford/ Motorcraft cat or O2 sensor. I have had problems with aftermarket stuff.

 

Well i already have aftermarket cats that i ordered for Troyer a while back, i guess its time to put them on. So do u think thats responsible for the high, odd idle? I also have plans to change out the o2 senors too cause i have a custom tune on its way.

 

With the cats stopped up the O2 sensors are trying to compensate the fuel/air ratio and can't because the cats performance is too bad. Great idea to put new O2 sensors on when replacing the cats. Good luck!

 

That i guess would be the reason for my milage hitting rock bottom. i get really crappy milage now, seems like i can practiclly watch the fuel gauge move with every mile i drive. Well we'll find out if replacing the four cats with the two i got from troyer fixes all my problems. Thanks~