TheSamba.com :: View topic - Subaru engine dies/searches for idle when coming to a stop

Sun Apr 14, 2013 2:05 pm

So i've put about 1,000 miles on my van since i did the Small Car based 2.5 conversion. Wire harness and computer were both supplied by Small Car. It's a 2009 drive by wire system.

Here's my problem:

Occasionally when i release the clutch to either slow down or come to a stop the engine dies. Other times it comes close to dieing (revs just go way low) then it recovers and idles fine. Most of the time it idles down nicely and settles into a 7 or 800 rpm idle (im not sure how accurate my Tach is) Also sometimes it seems to search a bit before it settles into an idle.

My first inclination would be to check/ clean the idle air control valve, but now i'm not sure it has one since the throttle is controlled by an electric motor...

Any thoughts? The engine runs great other than this little issue.

Sun Apr 14, 2013 2:31 pm

I had exact same problem with mine...turned out is was a faulty speed sensor

Sun Apr 14, 2013 3:46 pm

X2 on the VSS, not sure on the 2009 2.5 but the 2002 2.5 definitely needs one to avoid the issue you describe.

Sun Apr 14, 2013 4:06 pm

thanks guys i will look into it. Also, i haven't checked for codes yet, did your issue throw a code?

Sun Apr 14, 2013 6:54 pm

I have a similar thing happen with my 3.0 + aftermarket ECU

I replaced the fuel pump relay, and the fuel pump is only a few months old

now I am looking at this info from Link who made the ECU

Quote: When the throttle is abruptly closed the engine generates more vacuum than under normal conditions (such as idle and light cruising). This condition is known as overrun. During overrun the ECU performs a fuel cut by switching off all injectors. This helps minimize the possibility of backfires occurring and reduces fuel consumption and emissions.

In Link ECUs, the fuel cut is only triggered if the engine RPM exceeds that specified by the user for the current engine temperature in the 'Fuel Cut Activation RPM Table'.

The activation RPM must be set above the engine's idle speed so that fuel is not cut when the engine is sitting at idle with the throttle closed. In practice the activation RPM should be set around 500rpm above idle so that as the engine speed falls during overrun the fuel is turned back on early enough to stop the engine from stalling. A typical Activation RPM for a fully warm engine (80-100 degrees C) is 1500 RPM.

When the engine is cold the idle speed control system will typically be setup to raise the idle speed. As a result, it is necessary to raise the activation RPM at lower engine temperatures. Even if the idle speed is not increased during cold running it is still advisable to use larger activation RPM numbers at lower engine temperatures. This is because cold engines generally do not tolerate the use of a fuel cut especially at low RPM.

Note: This function may only be used if a throttle position sensor (TPS) is fitted and correctly set up.
http://www.linkecu.com/link-help-centre/glossary/over-run-def

not sure if I want to dig into the ECU programing myself, but this info could be a clue to my issue. it was also suggested that my crank position sensor could be over heating...from a random PepBoys counter guy...

defiantly seems to happen when the clutch is out and I'm slowing to a stop of about to downshift for slower traffic ahead. the engine is so quiet I don't notice it till it's already happened. but one time it seemed to be near dying and I revved it and it it came back.

I have no tach yet and no speed sensor. I was about to buy the RMW speed sensor kit and they told me I didn't really need it cause the TPS should provide that info/signal to the ECU.

after it dies and I roll off to the side, it takes about 5-10 minuets before it'll start again. but I think during that time when I turn the key I don't hear the FP werrrr just before I turn the key to turn on the starter motor.

I'd really like to get this issue nailed down. :lol: it's annoying ! I have alot of hills on my commute that don't require the accelerator pedal and I just roll down them...the throttle body is shut and that's often when it seems most likely to happen.

Brian, I don't mean to jack your thread, my situation is probably apples and oranges to yours...but maybe not. hope you don't mind.

Sun Apr 14, 2013 8:46 pm

Quote: Brian, I don't mean to jack your thread, my situation is probably apples and oranges to yours...but maybe not. hope you don't mind.

No worries.

What year is your 3.0? your not starting for 5-10 minutes is probably key in diagnosing your issue. Use that 5-10 minutes to check for spark, fuel, etc... also check and see if you have any codes.

Speed sensor seems to be a logical culprit for my problems, but i think you've got something else going on...

Sun Apr 14, 2013 9:06 pm

My problem was exactly as you first described, slowing down, clutch down engine would either die or "hunt" at very low rpm ( nearly die). Engine would restart first turn of key- every time, or if still rolling by dropping clutch- then no further problems for a day, a week- very intermittent.
A check of the speed sensor ( vanaru model that fits behind speedo) revealed no signal, new sensor and no further issues...simple as that :)

Sun Apr 14, 2013 9:41 pm

Brianfromutah wrote: Quote: Brian, I don't mean to jack your thread, my situation is probably apples and oranges to yours...but maybe not. hope you don't mind.

No worries.

What year is your 3.0? your not starting for 5-10 minutes is probably key in diagnosing your issue. Use that 5-10 minutes to check for spark, fuel, etc... also check and see if you have any codes.

Speed sensor seems to be a logical culprit for my problems, but i think you've got something else going on...

I thought it was an 06 but found a wire bundle with a blue tape label that said 05. but it's a JDM EZ30r with the black plastic manifold, 6 exhaust ports and variable valve timing and lift I think.

codes...heh, I do have a thing to read codes and stuff but haven't taken time to wire it in yet. I need to run a heavy protective conduit to protect the 3-4 $50ea. can-bus cables to the dash pod. :roll: :lol:
honestly I'm not smart enough to check for anything but how many people I'm pissing off in traffic when this happens.
once I get my display installed I can data log for 30 minuets of driving, that should help. or at least help a mechanic/tuner guy help me.

Tue May 07, 2013 7:19 pm

I have another question about the speed sensor fix... Does it always throw a check engine code? I had mine checked at autozone today. It had a bunch about the evap system, fuel level, neutral switch, but no speed sensor codes. I wonder if i have a different problem?

Sun Mar 27, 2016 12:59 pm

How do you check to see if you have a good speed sensor .. I am using the Gowesty Speed sensor with my Subie conversion and having problems at allow idle. I am going to recheck the wiring to see if maybe I have a bad connection. I am not sure who to verify if the speed sensor it working..

I am not sure this would really be the issue since my engine is hunting for idle even at start up.

Sun Mar 27, 2016 1:40 pm

I have the same issue. Usually after warmup. Push in the clutch, coming down from speed, and red dash lights come on. Stall. If I push in the clutch and keep my foot lightly on the gas pedal, even briefly, I can keep it from stalling, but it's a tricky operation.

I have the GW VSS installed. I'm thinking about using another means for the VSS, like the bracket and sensor near the CV bolts.

Sun Mar 27, 2016 4:05 pm

david2676 wrote: How do you check to see if you have a good speed sensor .. I am using the Gowesty Speed sensor with my Subie conversion and having problems at allow idle. I am going to recheck the wiring to see if maybe I have a bad connection. I am not sure who to verify if the speed sensor it working..

I am not sure this would really be the issue since my engine is hunting for idle even at start up. You should have some sort of OBDII reader. I use the Torque App on an android tablet. It is fun even when you don't have any issues, but great for seeing whatever the computer is.

If it is not the speed sensor, does your year have an adjustable throttle position sensor on the left side of the intake. Messing around with that affects idle. You could also try adjusting the throttle stop.

Sun Mar 27, 2016 5:18 pm

I had the same issue and it was related to neutral position switch. I believe I had to ground one of the wires. My engine is 98 EJ 22 and the donor had an automatic transmission.

Matt

Sun Mar 27, 2016 7:37 pm

I had this exact issue (08 2.5 DBW) that didn't have a VSS. Installing a VSS cured the problem.

I also use Torque, really easy way to check your VSS output if you don't have a real scanner.

Also, my van would loose power (cut to idle) if the throttle didn't move for 5 minutes. Lifting and pressing on the pedal would clear it. VSS instalation also fixed that issue. I could replicate it parked in neutral with a stick on the accelerator to keep it above idle for 5 minutes, helped with troubleshooting.

Mon Mar 28, 2016 4:40 am

I would use some throttle body cleaner if your throttle body is not completely gunk free. That can cause a poor idle/stall issue.

Mon Mar 28, 2016 3:29 pm

turned out all it was needed was a adjust meant to the idea screw. I was told never to tough this it was set by the factory. This engine is not the same as the factory its a frankin motor.. so I guess it needed just a touch more idle stop.

Thu Apr 07, 2016 10:18 am

I had this problem, as I mentioned previously. Cleaned my IAC solenoid, swapped it for another, cleaned the TB thoroughly, had VSS installed. No joy.

Last week, I installed a 130 amp alternator from a 2010+ Tribeca, and the problem is gone. I don't know if the two are connected. The previous alternator was showing 14+ volts, as is the latest one.

Go figure.

Wed Jan 09, 2019 2:50 pm

Forthwithtx wrote: I had this problem, as I mentioned previously. Cleaned my IAC solenoid, swapped it for another, cleaned the TB thoroughly, had VSS installed. No joy.

Last week, I installed a 130 amp alternator from a 2010+ Tribeca, and the problem is gone. I don't know if the two are connected. The previous alternator was showing 14+ volts, as is the latest one.

Go figure.

Forthwithtx - did your problem permanently go away with the alternator change, which is either getting more amperage to places that needed it, or which wiggled some wires to make things happy? Anything to report after another 2+ years?