Searching RPM Downhill
 

I just finally got over the p1131 and p1151 codes after going through the upper intake gaskets and isolator bolts, and now I have another problem. When I am driving down the interstate at 65 I am fine going up hill and flat. When I start to go down hill it feels like someone is pushing a brake (when running cruise and sometimes without running cruise). The Tach starts going up some and down some, it feels like it is searching and like it is kicking the truck out of overdrive. Any help would be great. The truck is a 2002 F150 4.2 V6 Auto, 97000 miles, New U-Joints, fresh trans filter and fluid, new MAF, IAC, Fuel Filter, Plugs, Air filter, and upper intake gaskets/Isolator bolts. Any help would be great...I just want to get this thing back to normal...thanks in advance

Is the speed changing at all??? I didn't quite get that out of your post, but it just seems that you need to have someone tune your truck or just tune the shift points. quick simple cheap fix (press the O/D) button thats all I can think of...anyone else??
~Phil

Thanks for responding. When this happens the speed does change up and down like 4 or 5 mph. I am just hoping to get this all figured out so the truck can be back to normal. we have two 2002 4.2 autos, so I have a little bit of a base line for how they should act, but I just can't seem to hit upon what is causing it. Does anyone know if something like this could happen if a Throttle position sensor could cause something like this, or even possibly a egr problem. thanks again.

P1151 fix
 

Longlow,
What was the actual fix for this? Was your intake leaking? Waht is the Isolator bolts? I just changed my engine and new getting a P1151 code. Not sure what to do. I reused the same harness and vacuum lines.

well the searching idle i still haven't really figured out, though i am thinking it is the throttle position sensor because i tried to clean it up some, and it started acting better (can't get the sensor out because of a stripped screw holding it in). But for the P1151 mine was the isolator bolts and the gaskets between the lower and upper intake (6 port gaskets) and the in gasket between the upper intake and the plenum. I can't make any promises, but it did fix mine...good luck, i hope it fixes your. by the way these are ford only parts.

I changed the Drivers front O2 sensor and the code didn't come back yet. If that doesn't fix it, I'll be looking at the gasket. Still don't know what the isolator bolts are.

the isolator bolts are the bolts that attach the upper intake to the lower intake. the nice part of changing these gaskets is that you don't have to do the lower intake. i did that on my explorer and it took forever and was not much fun. when i changed that 02 sensor, it stayed off for 4 days and then came back. i wish you luck, i tried every sensor that i was recommended to change, and after adding the gaskets, i was like 650 or 700 into parts. i am trying to change the throttle position sensor now, but i have a stripped screw, so i have to wait till the weekend. good luck