Hey guys,
I spend the last 2 and a half years to build a 2.5 Liter Subaru Beetle (check out my build thread (work in progress)) and I might say, that we are on the finish line by now...

Not everyting is fine with this beetle, I have some ECU problem that prevents the engine to run properly above 2500 RPM.
I hope you have some hints on how to fix it, because I am slowly running out of ideas.

But first of all the details:

The engine is a EJ25 2.5 Liter SOHC engine from a 2000 Subaru Legacy with 156 hp (Phase 2).

When I fire it up, it starts with a relatively high idle but then quickly goes down to a smooth idel at around 800 RPM.

When I start to open the throttle a bit, the engine starts to rev up slowly as one would expect.
As soon as it reaches 2500 RPM, it starts to run very rough and drops down to idle and rev up again and again (with no change on the throttle, still slightly open)

When driving the car, the behaviour is the same in every gear.
As soon as the engine reaches 2500, it stops accelerating (again with no change on the gas). Then suddenly after it dropped to 1800'ish, the acceleration kicks in again...

I also had some high revs when rolling in idle, but I fixed that by grounding the //Edit: Neutral //switch (B135 Pin 26 at the ECU)

Error Code says 24, but I cleaned and checked the IACV and it seems to work....

Any ideas?

Thanks in advance...

are you running a speed sensor for the ECU?

Yes, I do have a speed sensor.
It is installed directly inside the speedo and is wired to B135 Pin 24 (if I remember correctly).

Running the engine without the speed sensor was a total mess.
The engine was choking heavily when it reached 2500 RPM, dropping down to 800 and up again rapidly and it died almost every time I took my foot off the pedal.

We also did a test where we jacked the front of the car and manually rotated the front left wheel (to stimulate the speed sensor) while testing different revs...

Before we grounded the idle switch, this caused an automatic inscrease in RPM without even touching the throttle. This seems to be fixed now, but apart from that, it does not seem to have any major effect...

Maybe one more thing:
Once I pass that magic wall and reach let's say 3500 RPM, the engine runs smooth again and accelerates as you would expect (I changed gear at around 5000 because the engine has been rebuilt, so I did not check the rev limit...)

No expert but it could be a faulty map or maf sensor, are you able access fault codes?

depending on the ODB series I would be investing in the ODB cable and trawling the net for the diagnostics program....pretty sure its either dirt cheap or freebies are available if you look hard enough. I have ODB1 so I have a simple datascan tool that lets me check the inputs and outputs on the ecu - handy when your trying to find a faulty sensor

The temp sensor also forms part of the idle circuit (these fail and also get a white calcium like build up depending on how the motors been treated with servicing etc) along with the IACV and will do weird things with idle.
Another possibility based only on the fact that its a mechanical style sensor is the TPS.....these wear out and similar to fuel senders if you have a worn spot on one you will get nothing when the ecu is looking for a particular curve in signal/voltage.

if you can get the cable and program this will allow you to see whats happy and what is so far out of range its obvious. I believe with ODB2 you have the ability to change a couple ( not many) parameters

another killer in conversion world is grounding......make sure you have everything grounded.....having been rebuilt it may have a bit more sealant product or gasket material under areas that may be affecting the grounding simple fix is to make sure everything has a ground ie coolant manifold, intake manifold, motor to box and box to chassis/battery.....sounds stupid but subarus are finickey with ground....this is one of the simplest things to do as well......

crank sensor

Interesting that it's fine over 3500rpm which means it's not going into limp mode.
As Paul suggests a scan tool will help see which sensor is giving an abnormal reading.

Usually bad crank sensors cause starting issues and cam sensors they do that run at all (ask me how I know)

Wow, this is quite a long list of homework, thanks a lot!

I will be back on the car by Friday and I guess I will start with checking that everything is grounded properly and then work my way through the different sensors.
TPS is another good hint...

We checked the ECU error codes using the two black connectors, the check pin and a test light.
The resulting codes are 24 and 38.

38 is related to the (non-existing) torque signal from the gearbox and can be ignored as far as I know.
24 points to the IACV, but does not necessarily mean that the IACV is actually broken.

The ECU should have OBD2, so I think a simple scantool won't work here.

I'll keep you updated...

Hey guys,
I think I found the problem.

When I cleaned the throttle body, I took off the TPS and did not really know that I had to adjust it when I put it back on.

The TPS has slotted holes that allow rotating it back and forth, so I mounted it in a way that the integrated spring had minimal initial tension when the throttle was closed.
After we rotated the TPS and thereby increased the initial tension on the spring, the engine runs much smoother and does not drop and choke anymore as it did before...

Now that I looked it up, my ECU pinout sheet tells me that the voltage for the TPS has to be between 0.2V and 1.0V with the throttle fully closed and between 4.2V and 4.7V with the throttle fully open.

The ranges seem quite rough. Is that OK or does anyone have more precise values?

Hey guys!

I adjusted the TPS to be in the specified range for fully closed and fully open throttle position and the choking and stalling is gone.

So I think the 2.500 RPM produced just by coincidence the voltage that the ECU would expect as idle (or something like that...)

I did some more short test drives with the car and it seems to rev smooth now through all gears.

However, one problem still remains...
Sometimes, when I depress the clutch while rolling (e.g. when approaching a crossing or shifting gears during normal drive) the car revs quite high at around 2.400 RPM.
When standing still, idle rev is around 900 to 750 RPM (depending on the engine temperature).
So it seems to also depend on the speed sensor (which is installed)

We already grounded the //Edit: Neutral //switch, but someone told me, that there is also a "clutch switch" that has to be grounded aswell.

As there seems to be a difference between ECU from manual and automatic cars, I am a bit confused...
Has anyone ever heard about that combination "//Edit: Neutral //switch" + "clutch switch" ?


so long
chr

These Gen 3 ecus are not OBD2, they use the same diagnostic connector but a different protocol.

Have not heard of a clutch switch apart from on the cruise control.

I got this usb link off eBay http://www.ebay.com.au/itm/SUBARU-DIAGNOSTIC-USB-INTERFACE-1999-2008-OBD2-IMP...

It works on my brother's 03 Liberty and the 02 Outback parts car I have, both Gen 3. Software download online (FreeSSM)

Got a bit confused with your "Idle Switch", B126 pin 26 is the Neutral switch. I hook this up to a relay so when you hit the starter the ecu thinks the car is in neutral but when you come off the starter it sees the car is in gear. I think the rev limit is different between neutral and "in gear".

Would love to get a copy of your pinout diagrams the ones I have are very close but incorrect in some places/colours.

Is your ecu auto or manual?