Roush boosting at cruise

[Bozz]

Is this only on level surfaces, or are you going up an incline when it happens?

 

[martinitime]

Is this only on level surfaces, or are you going up an incline when it happens?

Both on hills and flat.

 

[Bozz]

If it was always on hills in cruise I could understand, but on flat.....got me.

 

[Vash]

I’d recommend data logging your fuel trims and working with a shop familiar with this application. I’ve been happy with JDM, but I’m not sure how much support you’ll get unless they are your tuner or you’re running one of their packages. Doesn’t hurt to see if they’ll take a look though. Surging usually indicates a tune issue, vacuum leak, poor throttle blade control, or an issue with your MAF sensor. Granted, the latter usually throws a CEL. Regardless, something is making your PCM think it needs to add additional air to the engine or you’ve got unmetered air after the MAF that’s accentuating any throttle adjustments the PCM tries to make to maintain speed.

The faulty supercharger bypass valve suggestion was a good one too as that’s also vacuum related and has direct control over boost.

 

[1BAD454SSv2]

Check vacuum line to Bypass valve , if you hava a bad hose and losing vacuum it will close valve and make boost.