Low cold idle, aftermarket exhaust?

[lifespeed81]

I've got a low cold idle (650-700 rpm) on my '89 325i that's stumped me, I have no stored codes and essentially all-new everything over the last 6 months. I have a new temp sensor (actually 2, to make sure the first wasn't faulty), ICV valve, spark plugs, TPS sensor, C191 connector, ignition coil, CPS, main/fuel pump/O2 sensor relays, distributor cap/rotor, plug wire loom, and I'm back to running the stock AFM (after reverting from a Miller MAF, and all wiring correctly reverted). I've gone through every vacuum line and potential air leak MANY times over.


Cold start itself is fine, though I typically don't get enough rpm's on start-up to clear the warning lights and have to give it a stab of throttle to clear them. Once the engine warms the idle raises a bit, but just to normal levels, and I'll occasionally get a stumble on cold gear change where the engine almost dies, but again no code is stored.


I'm running a no-name header into a Borla exhaust with a free-flow cat, and at this point it's the only thing I can imagine causing my low idle. Adjusting the idle via the adjustment screw just ends up causing a bouncing idle and not helping cold idle.


Any thoughts?

[Zambuzan]

I'm pretty sure the original ECU was tuned specifically for stock exhaust. But I also have a similar idle problem except the opposite: relatively high idle at cold start and when it's warm, but when I put it in gear it just idles normally. I'm all stock except headers+full exhaust, stock ECU.
If you're positive that everything electrical is properly working, then start checking little things like valve adjust. or cracks in rubber hoses. Or better yet just get a tune. Valve adjustment for me fixed my *original* bad idle, but headers *currently* still affect idle.
I'm no expert, but good luck!