I have a Mazda, with the ranger 3.0L flex fuel engine. I have two issues, but might be related.

When leaving my bosses house, truck starts and idles fines. When i go down bumpy driveway, it idles rough. I stop, and idle smoothes out. Does not matter how long i let truck warm up.

Second problem is very intermediate. Sometimes when under load, i can hear what sounds like a pre-ignition noise. It will continue into idle, then goes away.

Thank you
nate

 

What year?

Pinging/knocking(pre-ignition) is fairly common on the 3.0l, but not normal.

I would look closely at the EGR system.
It has 3 parts.
EGR valve, vacuum controlled valve, it opens to allow exhaust gases into intake, this cools cylinders when under load, yes, sounds odd but that is why it is there
Cooler cylinders means no pinging.
EGR Valve ONLY OPENS after engine is warmed up and when engine is under load at higher RPMs.

DPFE sensor, this tells the computer if EGR valve is open and by how much.

EGR Modulator/Solenoid, this is a 12volt vacuum valve, computer pulses 12volts to this device to send vacuum to EGR valve to open it.

EGR valve opening at low RPMs will cause misfires
EGR valve not opening under load will cause pinging.


Other things to look at would be general engine wiring.
Have engine warmed up and idling then start moving wires around, see if you can duplicate the misfires on bumpy road.

 

sorry, it's a 2000

 

I think there was a TSB around the early 2000's about Rangers that said the Coil Packs could cause pinging, the TSB had serial number range for the effected coil packs.

And there was also a computer software upgrade recommended if new coil pack didn't fix the issue, I assume it changed the spark advance profile.

Neither of these would be effected by bumps in the road though, lol.