RPMs dip while cruising, new engine...
 

So on my way home tonight I was on the highway going about 120 km/h when all of a sudden the rpms dropped from 4K to about 2K very quickly and then jumped back up to normal (probably only took a second). I was almost home already and continued on my way and it happened two more times, with each occurrence only lasting about 1-2 seconds. It feels like an instant shift from 2nd to 4th and back again as it feels harsh. Not like a drive train issue but it feels more like engine braking.

I just had the engine replaced from ForceFed with a Mazda Reman (I know, I know). They went through the intake (i.e. SSV and what not) and cleaned everything out. There's only 2000 Km's on it so far. They also replaced my clutch with the exedy OEM clutch and braided clutch line. New radiator as well. New plugs. Air pump was disconnected as well as EGR delete.

I installed BHR ignition and MSD wires, walbro 255 lph fuel pump, B&B midpipe, alternator, Optima redtop battery, Oil temp/Oil PSI/Coolant temp gauges all previous to the engine replacement.

I checked all the connections to the ignition/wires/plugs and intake, MAF, vacuum hoses when I got home and I didn't find anything weird. All my temps and pressures look good. Hard to tell though when the rpm drops happened because it was so quick. Oil temp 175F/ Oil pressure ~ 80/Coolant temp 175F.

I'm worried about driving it like this because the RPMs don't seem to match the speed of the vehicle and I'm concerned of doing damage. If the clutch was disengaging then the RPMs should shoot up as I'm under power. It's almost as if the throttle body shut and reopened or the SSV shut completely.

I'm gonna talk to the owner of ForceFed tomorrow about it but I would greatly appreciate any feedback you guys could throw my way.

TL;DR Engine forcefully drops RPM while highway cruising for ~ 1 second. There's not really any reason why it should.

Was it missing?...or fuel starvation?

There are so many things it could be.....you will likely need to check fueling and ignition when it is doing it to figure it out

Intermittent problems like that can be difficult to figure out..unless you can figure out how to cause it consistantly

Dannobre, I don't think it was missing or starved of fuel. It dropped RPMs quite harshly almost like an engine brake in a semi. I don't know if it will do it while just idling as I was just about home when it started. Like I said though I'm wary of running like this. With a BHR ignition, new plugs and walbro fuel pump I don't see why that would happen as well. Hoooo man this is frustrating. I'm ready to throw in the towel haha.

Get them to look at it...

Any CEL's?

Update: My buddy had access to a scanner and only found p0410 & p0420 codes which are from my midpipe and disconnected air pump so no problems there.
After he brought the car home and went to go and drive it again the car wouldn't start and the security light started blinking rapidly. All other electronics worked. So I did some researching and found that other rx8 owners have had their car die out on the road and then when trying to start again would have the same symptoms.
After checking the obvious culprits (battery, different key....) he found two connections going into the PCM weren't snapped in! So it looks like when swapping engines the guys just missed the two plugs and everythings back to normal.
Thanks for your help guys!

shiiieet good thing its all solved now playa! need to get a meet going soon havent had one in awhile!