Driving back from the desert today my truck must have done this a hundred times until I got close to the coast and cooler weather.
Driving along it would feel like the engine would die for second and then kick back on with a violent jerk. I would watch the rpm gauge and would see it drop from say 3500 to 1000 and back up as it kicked back in. The violent jerk seem to be as the rpms dropped and not when it picked back up. No engine light ever came on. I had it in at the Ford dealer for 8 days. They said it was the Valve body and so the overhauled it along with replacing the Mass air flow sensor and doing a Tune up. I had it back for a week, drove to the Desert again and it kept doing it so I took it back in. They can't seem to figure it out as it only acts up in extreme heat so they have never felt it. It really stresses my wife out. She refuses to go back to the lake with our daughters until I fix it. Help!
Thanks
Blaine

98 f-150
4.6 v-8
63500 miles
tows a 20' ski boat

 

let me get this straight....... you're rapping anywhere from 10 thousand rpms up to 35 thousand rpms?? and you haven't blown the engine? what's the problem??

 

yes, the rpms were a type-o
any ideas at all??

Blaine

 

Though I've never driven in the desert, isn't another difference besides 'heat' between the desert and the coast, 'dust'.

I had a transmission sensor problem and the problem seemed to occur after driving on unpaved roads. Not rough roads, just a lot of dry dust getting kicked up.

 

This may not be related but I had a similar thing happen to me. It was one of the fuses in the under dash fuse box. Mine is the 97 4.6 and should be similar to yours.
Check the 30-amp fuse that feeds the PCM and the Coil PACS (look in your owners manual). This fuse was not making good contact and so was causing all kinds of problems. Intermittent jerking is one of the things caused by this because vibrations from driving would break contact just for a moment. This may be especially true if you drive with the windows open in the desert. The heat will cause the already problematic contacts to expand and become loose. Since the computer is loosing current and being turned off, you will not get a check engine light. Also, it did not happen all the time. Finally the truck would not start and that is when I found the problem.
After posting this I found this to be a problem with other F-150’s. Some have found the fuses on the floor.
The fix for me was to bend the tabs just slightly out of parallel so they made better contact. I have not had a problem since.

 

Thanks for the info! I'll give it a look.

Blaine