Rpm's stop increasing when accelerating


Asked by Jan 14, 2016 at 03:00 PM about the 2007 Subaru Legacy 2.5 i

Question type: Maintenance & Repair

I purchased my 2007 Subaru Legacy around a year and a half ago, and
had to have a new transmission and head gaskets replaced. The car was
ran with bad head gaskets for several thousand miles, forcing me to
replace many external engine components as well, due to damage from
the oil. The old transmission was replaced due to extremely hard shifting
from second to third gear. 15,000 after all of the repairs, my car is running
great for now, and getting serviced regularly by myself including oil
changes, new air filters, etc. The new confidence I have acquired due to
my car running so well, I am able to "carve the roads" as one would say.
Since I am no longer afraid to drive my car how i want, high RPM's are
visited frequently. The car runs amazing, and shifts well in the manual
mode of the 4EAT. although it runs and shifts smoothly, there is one minor
    When accelerating from a stop, i usually allow my car to reach 5000-
5500 RPM's before i shift to the next gear. when doing this i notice
something very strange, which has confused my college automotive
professor, and even my mechanic. First gear follows through with
accelerating perfectly, having a even increase in speed and RPM's. Second
and third on the other hand, are quite odd. When in second gear my car
reaches an area between 3900 and 4200 rpm's where the car RPM's will
stick and stop accelerating for around 1 second, and then it continues on
accelerating to the shifting range into third gear. In third gear, when my car
reaches an area around 3400-3700 the car drops about 300 rpms, before
continuing to accelerate normally. All this happens with my foot pressing
the pedal about 75% down, and doesnt happen all of the time. This occurs
about every other acceleration, especially when going up a hill. The engine
light has not appeared, so we have no way of knowing how to fix this
problem. Does anyone have any suggestions?

2 Answers


Some cars have flat spots in the power curve. Have you done a tuneup lately? Use a good fuel injector cleaner as well.


Hmmm...I haven't encountered flat spot in midband except where an intermittent MAP sensor has failed, so check its connection, and remove to carefully spray-clean, as it's easy to do quickly. I'm assuming that new plat/iridium plugs and good wires followed the HG job, so, where this occurs in the midband, without CELs, I doubt it's misfire-related either. Was the tranny you introduced new or used? Regardless, drain its ATF and replace with 3.5 qts fresh ATF. If flat-spotting recurs I'd try swapping in a used TCU. Maybe check the main harness contacts above the trans too? Ah...I have another idea: the 2006+ motor uses variable-valve actuators to readjust the cam (and timing) when a threshold about 4k rpm is crossed so as to allow faster highway passing. This system is oil pressure-regulated, using somewhat fragile pressure sensors that sit atop each actuator (left front and right rear). I wonder if a leaking sensor (in addition to dripping oil everywhere) prohibits cam actuation and therefore gets the ECU/TCU "confused" as to how to proceed? (Note that a leaking switch will NOT set off a CEL, but a failed (or unplugged) sensor will indeed do so.) So check this VVT stuff first. The switches are about $13 online when needed. OTOH, this motor really LIKES living in the bottom half of the rev curve with the VVT system, saving lots of fuel and gaining nice perceived torque bump in doing so. If you can't get rid of this hesitation, and it only occurs c. 4k then learn to drive in "D" (except on icy downhills). It'll limit fast steep hill-climbing just a bit. Lastly, there may be a faulty solenoid or valve in the "new" trannie's throttle body, but you do NOT want to go there, eh? Good luck.

Your Answer

Add photo

Related Questions

  • Subaru Legacy 2001 bad acceleration 38 answers

    Well i have subaru legacy 2001, My problem is when shift the 1 or 2 Gear and then press the accelerator the acceleration RPM slowly slowly increase when it reach to above 1500 RPM then take pickup f...

    2001 Subaru Legacy GT


    Maintenance & Repair

  • What's the problem with my car's acceleration? 8 answers

    Okay I have a sever problem and I am unsure what to do about it. So I own a 1995 Subaru Legacy LSI 4 Door Sedan. As of the last yearish when I go to start my car it starts up fine and the RPM's go to ...

    1995 Subaru Legacy 4 Dr LSi AWD Sedan


    Maintenance & Repair

  • 2003 subaru legacy, noise on acceleration that goes away over 30 mph 5 answers

    2003 legacy makes a ticking or rattling noise on acceleration; goes away over 30-40 mph, think it is gas-related but not sure which part

    2003 Subaru Legacy 2.5 GT


    Maintenance & Repair

  • 1993 Subaru Legacy Issues 3 answers

    I've had my 1993 Subaru Legacy for about 2 years now, and it ran great when I first got it. After about 6months I started noticing that I was not getting a lot of power to my electrial instruments ( w...

    1993 Subaru Legacy 4 Dr L Sedan


    Maintenance & Repair

  • POWER PROBLEMS 5 answers


    2006 Subaru Impreza WRX STi Turbo AWD


    Maintenance & Repair

Search Subaru Legacy Questions

Subaru Legacy Experts

#1 Anthony_60
Reputation 960
#2 Nick Eidemiller
Nick Eidemiller
Reputation 670
#3 dandyoun
Reputation 590
View All

Related Models For Sale

Used Subaru Impreza"
242 Great Deals out of 8,290 listings starting at $1,995
Used Subaru Outback"
422 Great Deals out of 30,431 listings starting at $1,295
Used Subaru Forester"
359 Great Deals out of 19,905 listings starting at $1,099
Used Subaru Impreza WRX"
43 Great Deals out of 1,348 listings starting at $2,500
Used Honda Accord"
1,309 Great Deals out of 78,750 listings starting at $1,395
Used Toyota Camry"
1,651 Great Deals out of 98,959 listings starting at $895
Used Subaru Impreza WRX STi"
34 Great Deals out of 605 listings starting at $8,977
Used Honda Civic"
1,175 Great Deals out of 59,020 listings starting at $1,300
Used BMW 3 Series"
1,633 Great Deals out of 39,937 listings starting at $888
Used Ford Fusion"
1,458 Great Deals out of 79,631 listings starting at $1,450
Used Audi A4"
335 Great Deals out of 13,046 listings starting at $1,500
Used Honda CR-V"
1,597 Great Deals out of 81,716 listings starting at $1,695
Used Mazda MAZDA6"
251 Great Deals out of 15,242 listings starting at $1,450
Used Nissan Altima"
1,491 Great Deals out of 88,087 listings starting at $1,195

Used Cars For Sale

2017 Subaru Legacy For Sale
11,287 listings starting at $19,815
2016 Subaru Legacy For Sale
18 Great Deals out of 1,100 listings starting at $15,299
2015 Subaru Legacy For Sale
29 Great Deals out of 909 listings starting at $12,900
2014 Subaru Legacy For Sale
44 Great Deals out of 1,146 listings starting at $9,299
2013 Subaru Legacy For Sale
43 Great Deals out of 931 listings starting at $7,995