coolride

Anyone else having this issue?
My 03 4.2L (35,000 miles on a reman engine) with 5spd manual
idles a little high (800-900 rpm), aside from that, when it idles it runs rough. It isn't misfiring, no codes, just vibrates as if it is on the verge or a skip? Runs smooth at anything above idle. No misfire at all.
Aside from that, it has stock cats with a glasspack, nothing crazy, when you let off to coast or slow down it pops/cackles like an old carbureted hot rod? I didn't know fuel injected engines could do this? No big explosion, just a rumbly popping.
So here is what is new. engine was a used reman from another truck I had. 35000 miles on it. Cats were new with engine. New with engine install a couple months ago, upper intake bolt/grommets, upper intake gaskets, spark plugs and wires, pcv . Hoses all look good and well connected. Starts and runs fine otherwise. Just annoying at idle. I don't really care about the exh sound but not sure if its relevant here.
Things I tried, I swapped throttle body and IAC as I had others from my engine swap, no difference. Not quite sure what else to check?
Any ideas?

coolride

I think at this point I have done all I am going to do to this truck. It is dependable and it runs OK. And it is the last truck of this vintage I will be buying. At least with a 4.2L. May as well have the 5.4 or even thr 4.6 and have some power to go along with the 14-15mpg.
It is a complete waste of money to buy these v6 trucks if you think you will get decent gas mileage. And for me, this particular truck has been a pain, not all the trucks fault as the PO sold it to me with a list of issues that he didn't disclose to me. But my next truck will not be a v6 in a full size. v8 or nothing. These v6's are turds. Poor power poor MPG. Whats the point?

Tredeh

I know this is a late reply, but just to clear things up for anyone that might run across this post in the future.
If you're having a rough idle (And it drives fine), its best to try to clean the IAC and replace the TPS.

And FWIW, the 4.2 is a great engine. It's a ford V6, it wont blow you away but it wont let you down. It will pull whatever you can fit in the bed. Mine has 170,000 miles on it and runs strong. It makes more HP as the old 5.0 and nearly as much torque.
As for mileage, my 4.2 averages 18 in town and 22 highway.

willy j

I thought 850-875 rpms is spec at idle opposed from what the op said. agree with the last guy, my truck runs great for the most part just needs a little tlc.
2000f150 v6 4.2 232,000 miles on original clutch.

CombatPOG

Wow, I'm getting 17.8 mpg with 31s and a mis. I used my truck for work and Hot Shot small loads here and there and does what I need it to do. I have a couple more things to do to the truck to get it where I want it.

jasper22

Its your upper intake plenum leaking. Extremely common on these models. Will run smooth and then start popping thru intake/exhaust. May pop a lean code on 02 the worse it gets. Prob cost ya $150-200 in parts max. While in there replace butterfly actuator linkage clips, Dorman sells them.