Fluctuating Idle Issue - S54 swap

[E30Strube]

This is on my S54 swapped E30 M3. Stock E46 ECU (alpha N, deleted EWS), ebay headers, has vanos and drive by wire.

I have a fluctuating idle issue after the car warms up. At cold start up, the car idles completely normal. After a couple minutes, the cars idle starts dipping up and down by 200-400 rpms. Not sure if its related, but it will also go into safe mode (will not idle past 4000 rpms) once you start driving. I've tried the following:

Replace O2 sensors
Replace engine harness
Run ECU grounds to the chassis ground in the bay (e30 battery tray)
Redo C101 to E46 ECU adapter (based the wiring on FredKs thread and the tuner of the ECU, pretty confident it is good)

Known issue - the coolant temp sensor (e30 one) isn't grounded, so the dash isn't displaying the temp. I painted the block and the motor mount arms, so there isn't a metal to metal connection behind them. I ran a ground wire from chassis to mount, and then another one from that point to the block. The only CEL present is for the O2 heater circuit. This leads me to believe the car isn't going into closed loop, but I don't know why.

Can anyone offer some assistance here and point me down a path of what to check? :(

[Andrew325is]

Have you reset the throttle adaptation in the ECU? (via DIS or manually) If not, it will for sure go into safe mode. The uneven idle could just be due to the alpha N. You could try connecting a MAF if the ECU will still receive the input. If it runs rough be sure to check the coils. :)

[E30Strube]

What about synching the throttles themselves. I took the TBs off completely (including the bar that links all of them). I had to do the adjustment on the S14 when I took them apart, but haven't seen instructions on for the S54. If they were off, could that cause idle issues? Any ideas of instructions on how to actually adjust them (dial indicator, etc).

[Andrew325is]

I would follow BMW's instructions in TIS for throttle adjustments. It may also be in the E46 Bentley but I don't know. Either way the adaptive throttle learning program in the ECU has to be reset any time you replace a throttle position sensor or accelerator pedal. Instructions & additional info here: http://forum.e46fanatics.com/showthread.php?t=54763

[E30Strube]

When I do the reset as in your link, the idle smooths out and the car operates fine. After flooring it or driving it hard (going above 7000rpm), the car goes back into "safe" mode. Its almost as if the throttle adaption doesn't take. I found some info on the stages of "safe" mode and I appear to be at Stage 2 (ie. the car only goes to 4000rpm). I also followed the TIS to adjust the butterflies. Everything seems to be good with them now. Since the reset does smooth out the idle and restores power, I think I am at least finally on the right path.

[nrubenstein]

Where are your o2 sensors? Any exhaust leaks? The symptoms indicate that it is running poorly WHEN it switches to closed loop. Have you spoken to whomever tuned it? Have you tried running it with a MAF? (I know this means you have to swap manifolds, which is a bit of a pain, but would indicate whether or not you have an issue with the AN tune.)

Edit: have you tried running it with the O2s disconnected?

[E30Strube]

It does seem like the issue is when it switches to closed loop or tries to at least.

The O2 sensors are located at the end of the header. The tune will not work with a MAF as per the tuner. I've also tried the ECU in a stock E46 M3 and the car did not experience the idle issues I have. The car runs the same whether the O2s are plugged in or not. I've changed the O2 sensors to new ones, verified they are going to the correct pins and are in fact the pre-cat sensors. I'm getting codes for O2 sensor heater circuit. I thought it may be a grounding issue, so I even put the grounds for the sensors directly to chassis ground and that did nothing.

[nrubenstein]

It does seem like the issue is when it switches to closed loop or tries to at least.

The O2 sensors are located at the end of the header. The tune will not work with a MAF as per the tuner. I've also tried the ECU in a stock E46 M3 and the car did not experience the idle issues I have. The car runs the same whether the O2s are plugged in or not. I've changed the O2 sensors to new ones, verified they are going to the correct pins and are in fact the pre-cat sensors. I'm getting codes for O2 sensor heater circuit. I thought it may be a grounding issue, so I even put the grounds for the sensors directly to chassis ground and that did nothing.

So, it starts doing the idle hunt, even when it has NO O2 sensors hooked up at all? If that is the case, perhaps try disconnecting the DME coolant temp sensor? (Or anything else you can think of to force it to stay in open loop mode.) I'm also wondering if the E30 coolant temp sensor is the only one that is having issues due to paint?

Finally, what are you reading the codes with? Are you using a GT1, or other real diagnostic tool, or something more generic like an OBD scanner and/or Peake Tool? The Peake is better than an OBD scanner, but it is nothing like what you will get when you hook up a real diagnostic tool.

[E30Strube]

The e30 coolant sensor is the only one that has only a single wire going to it for grounding I believe. Will get the code definitions...

[Andrew325is]

It sounds like you're on the right track. For the coolant temp sensor on mine I just tapped the top of the thermostat housing. Use a 1/2 inch drill bit to make the hole then tap it with a 14x1.5mm tap (Snap-on has them). It's not thick metal so just be careful.

[E30Strube]

I'm using this



Because the E30 sensor doesn't have a wire ground, and the pipe piece is insulated on both sides via the rubber o-rings, the sensor doesn't get grounded. For anyone that uses this, they should weld on a small stud to attach a ground wire.

[nrubenstein]

For the moment, wrap a wire around and run it to ground? It's half assed, but it's a quick solution for testing.

[E30Strube]

For the moment, wrap a wire around and run it to ground? It's half assed, but it's a quick solution for testing.

Thats what I did ;) And it works. I will fix it properly whenever I decide to flush the system sometime. That time is not now lol.

[E30Strube]

These are the last codes:

P1122
P1222
P0506
P0030
P0050
P0036
P0223
P0122
P0056

[gobuffs]

Im having a similar issue. Appears I have a noisy TPS signal causing the computer to think I am pumping the pedal ad idle. Hopefully I can fix it tonight for Ofest.