S52 ... idles fine for 10-15 secs then bounces around and throws CEL O2 code

[singh336]

I just swapped in a OBD1 S52 in my e30.


21.5 injectors

OBD1 intake

3.5" MAF

lightweight flywheel

full exhaust + headers straight through mufflers. O2 is in headers.

And a TRM chip for all these mods.


car is a 90 325i




It idles fine for aobut 15 seconds when warm and then out of nowhere the idles dumps down hard sometimes it will stall if my foot is on the brake... it will bounce around and hunt for idle and then steady out but idle a little bit rough until i get going again and drive... then the CEL goes away.

If i stomp test the code its an O2 code 1222 i believe.. not sure but its definitely an O2 code.


O2 is definitely good, when I bought the motor the guy was running his own independent fuel pressure regulator on his car mounted externally from the engine and fuel rail. I think he modified the stock FPR on the rail to be straight through / bypassing it.

I found out the hard way and I had to swap a stock FPR in the rail to get it to run again....


So this is my only issue..


Anyone have any ideas?

[328ijunkie]

Obd1 O2 sensor code is almost never the O2 sensor. It ususally Vac leaks/fuel issues.

[berlow94]

I have the lightweight flywheel and TRM tune for it in my s52 swap whenever I unplug the battery and plug back in (resetting the ecu) the idle is always kinda funky for about 10 miles of driving.

[BenM]

Bad MAF or vacuum leak.

[singh336]

if i unplug the maf and let it idle then it should idle steady if the maf is bad right?

I'm going to try that, and then thing I"ll try is look for leaks but i doubt it, the car idles fine...


and it pulls great and smooth so i doubt the maf is bad.

[singh336]

I have the lightweight flywheel and TRM tune for it in my s52 swap whenever I unplug the battery and plug back in (resetting the ecu) the idle is always kinda funky for about 10 miles of driving.

Yeah thats understandable, I doubt that's my issue right now tho

[NickL]

Sounds like a vac leak

[singh336]

update:

found out the evap line to the bottom of throttle body wasn't clamped well enough and vibrated off.. wtf


car runs 100% now... amazing.

[e30rapidic]

awesome!