AT Turbo 'Power Mode' issue

I've been looking around for this problem with very little luck and having problems duplicating it for the mechanics.

 

I have a 94 AT Turbo that has recently started randomly going into the power mode. The power light on dash lights up and the car revs up so it's essentially doing what I understand the power mode is supposed to do. But it's doing it while going random speeds, both with acceleration and w/o, on hills and on flat, slow speeds and highway...you get the picture. The only constant was that I had to drive it for awhile for it to happen, but yesterday it did it while still fairly cold. It will go in and out of the power mode several times and then be fine again, then a little bit later it does it again. I have an up to 1 1/2hr commute one way, about half hwy. Some days it does it only a handful of times both ways, others its very frequent, almost non stop at times.

 

Between my brothers and I we have 4 Subies in family but mine is the odd ball as a AT and the 2.2 turbo. They're stumped and the Subaru dealer can only determine that it 'could be' a speed sensor, the wire harness or the tranny needs to be rebuilt/replaced. I've been trying to get it looked at by a tranny shop that the local independent Subaru shop recommended (they don't handle ATs) but I can't get it to do it consistently enough for him to do a test drive. It does it the most when I have to go to work but we haven't been able to duplicate it on my days off. FIGURES! Engine and turbo running great, all of those kinks were worked out after I bought it last year and with recent servicing.

 

Another Subaru shop further away has been recommended and I'm going to try to get it in there but figured I'd spread the search out to you guys. I know my car is rare but hoping someone has had this issue.

 

Thanks!

Personally I have never dealt with this problem but others have. It could be a problem with your throttle position sensor (TPS). There is a procedure to test and adjust your TPS, however, they come adjusted correctly from the factory and I have heard that they are somewhat difficult to adjust and if possible it is easier to just swap on another one if you have access. But, our turbo leggys are so rare that is not usually an option. I can't say for certain that this is your problem.

 

Also, the power light can also indicate a problem with the transmission and can give trouble codes. It will flash codes and can tell you if it is a speed sensor going bad, shift solenoid, etc. I would try this out to maybe pinpoint the problem if there is any. Here is how to check for possible trouble codes from surrealmirage (aka legacy777 from bbs): http://www.surrealmirage.com/subaru/trans.html#transtip

 

These instructions should work for any Legacy from 90-94, or ones that have the power light. The newer models will most likely require a scan tool. These instructions I believe will also work on the SVX as well.

The "Power" light indicates transmission codes. The following self diagnosis will show any fault codes for the transmission.

 

Check TCU trouble codes

To perform the self diag test for EXISTING problems

To perform the self diag test for PREVIOUS problems

 

There is also a way to make your power mode stay on permanently, which may be a last resort option for you. The Japanese Domestic Market (JDM) Legacies & SVXs supposedly had power mode on all the time.

 

Does the problem go away if you press the Manual shift button and stay in 3? Just curious.

 

Here is the FSM procedure for testing the TPS.

Thanks Monkey,

The TPS I will look into, first I've heard on that, I'm guessing this could be misreading that throttle is changing position even when it's not? Because it happens even with steady pressure on accelerator. The mode change has even happened a few times while stopped at a light. I was stopped at a light on an incline where I sometimes take foot off brake and flex it real quick, this time a couple seconds after I did the power mode engaged and I 'hopped' forward, luckily was at front of line & barely had foot off brake. We've felt it do it other times, but had foot on brake. Subaru service center kept talking about the speed sensor, but the throttle sensor has never been mentioned. I did have a busted injector but it's been replaced, believed to have been broken by dealer mechanic during diagnostic visit.

 

I actually did find that transmission flash code page last night, was too late to check it out. My son and I plan to do that first thing today. I knew that the power light would flash codes if any issues but mine hasn't really 'flashed'. Mostly it's obvious light's on because it's gone into the mode; RPMs go up noticeably, car surges forward, then RPMs drop again. Pause, repeat..

 

If anyone else has other suggestions I'm all ears, this is driving me nuts!! Disability has made it so I only do the basics on my car now but my 'family mechanics', (a.k.a my son & brother), who breath this stuff & do most of the work themselves, are stumped also.

 

Thanks!

If the TPS is out of calibration that could be giving bad info. It is a potentiometer of sorts.

 

The first gen turbo leggys are great as you know, but one thing that sucks is that the Subaru techs have most often never dealt with them so when they run into a problem that isn't completely obvious we as owners have to do most of the research to figure out what the problem is. A great resource for first generation Subarus is legacycentral bbs. http://bbs.legacycentral.org/index.php

 

The amount of information on that site is astonishing, to say the least. There are some major experts over there. I'd recommend checking it out and signing in.

Well, we did the test for tranny trouble codes. When doing the existing problem instructions it just kept flashing, no pauses, we stopped counting at 50. When we did the previous problem test it flashed only 6 times (codes on list are 11 - 33). Yes, we repeated the tests several times to make sure we did it right, same result.

 

We talked to the recommended shop. They've got a guy who specializes in the older Subaru, but he's on vacation this week. They want to keep it for a couple days & have him drive it home as his commute is similar enough to mine that it might trigger the problem. About the only way they can dedicate enough drive time to the problem.

 

I'll keep researching it and then give him a try next week if we don't figure something out before then. I'll check that site out tonight.

At least that may rule out some things. Are you going to check the TPS?

Yes, planning to check the TPS, but my husband needs to bring the meter home from work so will probably have to wait until this weekend.

Let us know how it goes! And if you get a chance post up some more pics of your Touring Wagon. It looks like a beauty from your avatar pic. How many miles are on it and where did you find it?

Update: We tested the TPS and the numbers do seem off a bit. However, when he went to unplug the harness it seemed very loose. Plugged it back in and when unplugged again it had the resistance you'd expect. So, we're going to give it a few days of driving to see if it acts up any more before we proceed any further. We'd not checked the connections because the Subaru dealer said they'd checked all connections....

Will keep you updated.

I'll post some pictures now. Not the greatest, just some taken in driveway the day I bought it, we plan to take more soon.

I hope your problem goes away. It also wouldn't hurt to use electronics cleaner spray to clean the connections in case some gunk got in there. It comes in a can from the parts store and is about $6.

Thanks, I'll try that too.

Oh and I purchased it locally, about 20 mins from home, from a used car dealer that sells the older trade-ins for the Subie dealer near by. I'm the second owner, first one only got rid of it because he bought a brand new one. It has 184K miles on it, put about 11k on it since I purchased it July 2011.

Update. Car's in shop now. Wasn't the loose connection, but still think it's probably the TPS. Family mechanics don't have time to work on it and with my bum leg I can't anymore. Took it to a local shop that specializes in Subaru, AWD Auto, we'll see what they say. I just want my car working, haven't hardly driven it in weeks, it's terrible!

 

I finally put up some pictures:

http://legacygt.com/forums/showthread.php/my-94-turbo-touring-wagon-193753.html?p=4089691#post4089691

Hopefully you get your subie back soon and get to have some more fun with it.

What was the fix? How did it turn out? Cause I'm having the same problem

So sorry, I could have sworn I'd come back and posted the solution!

With my car it was both the Throttle Position Sensor and the Speed Sensor in the gauge cluster, which meant replacing the whole speedometer assembly since it's built in. It was the combo of problems that was making it so hard to figure out.

 

I've also had to replace both the Knock & Mass Air Flow sensors in the three years I've had it. Then just this year a solenoid in the AWD went bad, caused feedback and fried the Traction Control Module. If you have an old turbo you know this is a hard part to find, the hardest by far of everything that has been needed. A few other kinks had to be worked out too. It's been an expensive couple of years as I'm in an apartment so all work was done at a local shop that specializes in AWD, especially Subies. It's running great now, hit 200k this summer and I'm definitely enjoying driving it!

Oh, and we're up to 8 Subaru in the family now. My nephew and son just got their first, my brother added a 3rd to his garage.

Good luck and thanks for the help!