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Old 04-08-2006, 02:11 PM   #1
spectre_25gt
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Default Engine RPM falls very slowly / bad throttle resp.

There are a lot of things going on that seem to be connected. The engine just doesn't feel like it's doing what it should be doing. I haven't driven many Subaru's however, so some of this may be normal.
  • When I upshift, I get a big jolt because the RPMs fall so slowly that things don't match up. It almost seems as if the engine doesn't want to rev down at all. I end up waiting 2 seconds or so before letting my foot off the clutch after a shift. (shouldn't the engine rev down smoothly to match after reengaging the clutch anyway?)
  • I've noticed that when I'm off the throttle, there doesn't seem to be a lot of engine braking power.
  • Transissioning smoothly from off to on throttle is impossible under 3000RPM. I get a jolt forward as if I had mashed the gas. Letting off the throttle can be difficult to do smoothly as well, but nowhere near as bad.
  • Once in a great while the engine RPM won't drop at all in between shifts. It'll be stuck at whatever it was at when I disengaged the clutch. It will only drop down when I reengage the clutch and then it will finally match the speed that the gearbox is turning. This has only happened twice since I've owned the car.
  • Lastly, every once in a while after shifting into second, I will feel a lack of power for a moment and then a kick. At that point it will feel normal for other shifts. At first I thought it felt like the clutch only half engaging and then engaging fully, but I realized that the RPMs match the speed I'm at.

The only thing I can think of right now is a possible vacuum leak. Maybe enough of a leak for air to bypass the throttle once a certain amount of vacuum had been reached? That seems a bit far fetched, though, as there would have to be a substantial leak for that to happen.
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Old 04-08-2006, 03:29 PM   #2
sha_zapple
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What kind of car? what have you done in terms of maintenance recently?
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Old 04-08-2006, 04:01 PM   #3
spectre_25gt
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Heh, right. I guess not everyone in this forum is driving a legacy.

I drive a 1999 Legacy 2.5 GT LE 5spd Manual. The last maintenance I did was a new viscous coupling and a new clutch about 3 weeks ago.

These problems have been going on for a long time, though. Since I bought the car, really. I guess I was just more enthused with having a new car and more ready to overlook problems at that point.
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Old 04-08-2006, 04:16 PM   #4
fibuz
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  • When I upshift, I get a big jolt because the RPMs fall so slowly that things don't match up. It almost seems as if the engine doesn't want to rev down at all. I end up waiting 2 seconds or so before letting my foot off the clutch after a shift. (shouldn't the engine rev down smoothly to match after reengaging the clutch anyway?)

    I think you still have to rev match using the gas, unless you're really letting out the clutch slowly it'll go wherever the engine should be at. May be sign of clutch going?


  • I've noticed that when I'm off the throttle, there doesn't seem to be a lot of engine braking power.

    Replaced the fluids recently? What kind of fluids are in there?


  • Transissioning smoothly from off to on throttle is impossible under 3000RPM. I get a jolt forward as if I had mashed the gas. Letting off the throttle can be difficult to do smoothly as well, but nowhere near as bad.

    Really sounds like either clutch problems or some kinda of aftermarket clutch.


  • Once in a great while the engine RPM won't drop at all in between shifts. It'll be stuck at whatever it was at when I disengaged the clutch. It will only drop down when I reengage the clutch and then it will finally match the speed that the gearbox is turning. This has only happened twice since I've owned the car.

    Dunno here...

  • Lastly, every once in a while after shifting into second, I will feel a lack of power for a moment and then a kick. At that point it will feel normal for other shifts. At first I thought it felt like the clutch only half engaging and then engaging fully, but I realized that the RPMs match the speed I'm at.

    Turbo lag


  • The only thing I can think of right now is a possible vacuum leak. Maybe enough of a leak for air to bypass the throttle once a certain amount of vacuum had been reached? That seems a bit far fetched, though, as there would have to be a substantial leak for that to happen.

    Sounds viable, but probably not likely. I'd check any hoses involved anyways, check fluids, clutch, etc. has this always been your car, how long have you owned it? do you know whats been done to it?
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Old 04-08-2006, 04:44 PM   #5
GTWagon_Phreak
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97 LegacyGT Wagon 4EAT

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My car is a 4EAT, but I experienced some similar issues to you. Coming from a stop with light throttle (~1/3), it would hesitate and pretty much get stuck for several seconds until I let off the throttle and got back on it. It was also not smooth at all at low RPM's when accelerating. Looking back on it, there was also a lack of power when increasing throttle and it would slowly kick in.

One day I pulled my TPS to check it, looked fine on the multimeter, put it back and the sensor was FUBAR'd & threw a CEL. Not sure how or why, but it stopped working properly altogether. Had a buddy who up his scanner to it, getting sporadic readings from the TPS. Replaced it, installed & adjusted, now is running like a champ; way better than ever before. Throttle is much more responsive and occasionally I do still notice a bit of hesitation off the line with certain amt of throttle, but I'm attributing that to the original fuel injectors which may have been cleaned once in 206K miles (other than pour in cleaner of course). Gotta send those off to be re-flowed eventually
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Old 04-09-2006, 03:18 PM   #6
spectre_25gt
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So your car wasn't throwing any codes even though the TPS was bad? Interesting.

One thing that annoys me about having an OBDII car (had a 90 240sx before this one) is that everyone tells me it's running fine just because they don't see it throwing a code. What ever happened to mechanics getting a feel for the car?

I've owned this car for a little under a year now.
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Old 04-09-2006, 03:32 PM   #7
subiekid
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I doubt this is the problem, but have you tried adjusting the IAC? To adjust it you need to loosen the two screws on the top of the unit, then rotate it. I don't remember which way will allow more or less air.
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Old 04-09-2006, 06:23 PM   #8
GTWagon_Phreak
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Quote:
Originally Posted by spectre_25gt
So your car wasn't throwing any codes even though the TPS was bad? Interesting.

One thing that annoys me about having an OBDII car (had a 90 240sx before this one) is that everyone tells me it's running fine just because they don't see it throwing a code. What ever happened to mechanics getting a feel for the car?

I've owned this car for a little under a year now.
Yep, no codes. I even took it to the dealer for a 30K mile tunup; new plug wires, plugs, tranny fluid, coolant change, brake flush, PCV valve, etc etc. I told them specifically to look into the hesitation I was experiencing and they said everything was fine I even asked them to check out a list of sensors, but I'm guessing they just checked the computer for codes on those sensors. If I had the kind of expertise they are supposed to and looked at the symptoms I listed out (wrote about two paragraphs, printed out, and gave copy to service mgr & left a copy in car), the first thing I would have checked with a scanner was the TPS and a couple other sensors. Had they looked at real-time TPS values, they would have seen how it was not reading consistently from 0 to 5 and told me that was the problem.

Good luck, let us know what you find
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Old 04-10-2006, 10:02 PM   #9
spectre_25gt
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How much did it cost you to have the TPS replaced? If it's not expensive, maybe it would be worth it just to replace it to see if that helps. I don't like being a part replacer, but I just don't have the time to fully diagnose it.

Thanks for all the help, btw. It's nice to know I'm not imagining it
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Old 04-10-2006, 10:20 PM   #10
GTWagon_Phreak
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97 LegacyGT Wagon 4EAT

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I ordered mine from SubaruGenuineParts.com, came out to be a bit over $80 shipped. Easy to replace yourself, just unplug the harness and remove two screws.

CAUTION: The screws strip really easy. I'd just replace them with new screws when you are done. If you want I can go look at the exact size they are as I bought multiple extra after not buying the right size the first time.
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Old 04-11-2006, 07:56 AM   #11
Gil
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my rpms also take a long time to fall when it's cold. leaving work, there's a single lane road that streches probably 100 yards right after a stop sign where i can just coast.

crawling along at 10mph, it could take me as long as 3 or 4 seconds for the rpm to return to normal idling after i throw it in neutral after moving off from the stop sign.
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Old 04-11-2006, 08:49 AM   #12
GTWagon_Phreak
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97 LegacyGT Wagon 4EAT

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When its cold is a whole other story. When its cold out my car runs a fair amount rougher and the 4EAT doesn't let 2nd-->3rd shift as early in order to keep the revs up & warm the engine faster.
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Old 04-13-2006, 04:54 PM   #13
spectre_25gt
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Are you driving an automatic then? I wonder if the cause might be different in that case.

I'll have to think about this for a while. I really don't want to put any more money into the car right now than I have to. I'm saving for a trip to California and I won't have a whole lot of income till I get out there.
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Old 04-13-2006, 06:24 PM   #14
GTWagon_Phreak
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Yes its a 4EAT; I said that earlier and its listed in my info
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Old 04-16-2006, 01:07 AM   #15
spectre_25gt
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Sorry, I still don't know the engine codes for these cars yet. I'm guessing that's what the AT is for, though.

Well, I went for a drive tonight and the problem is getting worse and worse. I've noticed now that I can't modulate the throttle very well at all. It's become very on / off. I'm leaning towards the idea of a bad throttle position sensor, but it almost seems like the mechanical feel of the throttle has changed, too. It's very easy to depress the pedal until I get to about 1/4 throttle. Until that point, it really doesn't give me any response, either. If I hold it at 1/8th it will, of course, rev up a bit, but it takes a good amount of time to do so. After 1/4, however, the engine races very quickly and it's very difficult to match shifts.

I need to bring it in for an oil change already, so I think I'm going to make a bit of a fuss about it. As I've said before, normally they don't want to do anything if there's no code being thrown, but this is just getting under my skin way too much.
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Old 04-16-2006, 07:19 PM   #16
GTWagon_Phreak
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Check the throttle cable too. Go into the engine compartment with the engine running and open the throttle plate manually from there. It could be the throttle cable itself or something too. If you know anyone with a code scanner that can read sensors in real-time, you can monitor the TPS value and see what it does as you get on the throttle.
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