Hello, this is in regards to my 88 Turbo II S4 with an S5 turbo swap.

I've been experiencing an issue where while crusing and either in boost or out of boost (doesn't matter) I will get a sudden lack of power and jerking as I continue to depress the pedal. It almost feels similar to fuel being cut. If I give it a little more throttle it kind of powers through this feeling and drives normally and then it will start surging again.

Some Background:
2 550CC Primaries
2 720cc Secondaries
All cleaned and flowed tested with only about 5 miles on them.
New TPS from Atkins Rotary
Freshly Built Hybrid turbo with EWG from BNR
I'm currently an RTEK 1.7, this issue could simply be the car needing an ECU and tune but I still feel something else is going on. Any help would be greatly appreciated thanks.

 

Fuel, air, spark.

Air sounds like it's probably good.

You say it feels like a fuel delivery issue, how's the filter, pump, and lines?

 

The Pump is a walbaro 255, it has maybe 5-6k on it as well as the filter and lines.

 

Spark plugs are less than 500 miles.

 

I've also checked ignition timing and confirmed that is good, the only thing I can possibly think of is I have TPS incorrectly set in someway.

 

More likely to be MAF or tune than TPS..

Does it pop or backfire?

 

Technically after fire yes. It occurs around 4-5k RPM when I let off the throttle, it will jump very rich and spit out some flames.

 

Anyway I can check the AFM and ensure proper function? Right now the AFM is mounted to the turbo inlet via a 3" stainless pipe. The is defiantly larger than stock maybe the RTEK can't properly handle the uncreased airflow?

 

You can see here my intake setup with factory S4 Turbo AFM

 

This is the kind of after fire present currently, AFR jumps to about 22.4 when throttle is let off after slight boost.

 

mine would surge at part throttle too, i think it was in closed loop, and all the mods made it a bit lean, so instead of the 02 cycling and its not noticeable, the engine goes from a little lean to not running to a little lean. it isn't really anything to worry about. you could try unplugging the O2 sensor, and see if it changes

 

Sounds like you're on the money.. I had to tighten the spring in my AFM on my Mx6 turbo to run extra boost without it hitting fuel cut.. Now its a bit surgey under closed loop/ light throttle cruising, even with no O2 sensor.

 

I tried unplugging the o2 sensor, surging still persisted. How can I adjust the AFM?

 

Try unplugging your IAT sensor. Mine was doing the exact same thing and it stopped as soon as I unplugged it. Still need to replace it, but it runs fine without it.