Toyota RAV4 Forums banner

Complete loss of power at 12,000 feet; idle relearn? ECU reprogram?

5K views 22 replies 7 participants last post by  SkySkier 
#1 ·
Hello,

My wife and I bought a 2010 RAV4 4WD 4cyl for an extended driving trip (from USA to Chile). In Guatemala, at 12,000 feet altitude, the car suffered such severe power loss that it couldn't go up a hill. Obviously, this is a problem for us as we will be at 16,000 feet at times during our trip.

I thought that perhaps the ECU could be reprogrammed for altitude, but the dealer in Guatemala said that this wasn't possible. They cleaned the throttle intake and suggested performing the idle relearn procedure at a higher altitude. FWIW, we bought the car used, and it came from sea level.

For the idle relearn process, the dealer said to disconnect the battery, wait a few minutes, start the car, and let it idle for 15 minutes. I can't seem to find a reference to this procedure for the RAV4 online, other than a slightly different procedure recommended on this forum (pull some fuses rather than disconnect the battery).

So, a few questions:
Has anyone else experienced similar altitude problems, and how did you fix them?
Is there a definitive process for the idle relearn? At what altitude should I do it?
Is there any way to remap the ECU for altitude?

Thanks for your thoughts,

Mike
 
See less See more
#2 ·
One member here got rid of their 4 cylinder RAV due to similar conditions in Colorado. Air was so thin the engine just couldn't "make the grade" so to speak. All normally aspirated engines will lose power at such altitude. There is no fix other than forced induction (turbo/supercharger) that I'm aware of. They bought a Hyundai Santa Fe Sport 2.0 Turbo by the way.
 
#4 ·
All you can do is go to a lower gear and make what headway you can. There is a Top Gear episode where their cars are experiencing the same as you at high altitude. Even the lads are having trouble drawing a breath.
 
#5 ·
The formula for horsepower loss due to altitude is ‘elevation x 0.03 x horsepower at sea level.’

At 12,000' your engine is down 64 HP from what it would be at sea level. That means you are down to 115 HP but that does not represent the horsepower at the wheels. At the wheels is even less due to frictional losses of the drivetrain, etc. With that loss you are now down to approx 90 HP +/-. Climbing to 16K feet will be quite a struggle.
 
#6 ·
The formula for horsepower loss due to altitude is ‘elevation x 0.03 x horsepower at sea level.’
Don't forget you need to divide the result by 1000. E.g.

HP Loss = (elevation x 0.03 x horsepower at sea level)/1000

I did not know that formula for naturally aspirated engines before today (thanks!) and would not have guessed it to be linear. It appears to be 3% loss in horsepower per 1,000 feet of altitude above sea level.

My understanding is that turbo engines suffer a LOT less power loss at altitude, but in my quick research I couldn't find a formula for that. Maybe it depends on the specifics of the turbo system being used.

.
 
#7 ·
A little depressing, although it seems that HP loss is only part of the problem. 90HP should get out over the hill. I think that the ECU's response to the atmospheric pressure/lack of oxygen is a larger component. It's simply not giving the care any fuel. I'm going to try to source a freer flowing air filter. Are there supercharger options for this engine? I could probably have the work done in Quito.
 
#9 ·
Not that I'm aware of. A supercharger or turbo would have to be fabricated as in a custom install. How are the other cars around you dealing with it? Maybe there is more to this than just altitude. Certainly that's the biggest culprit but how do other vehicles make it there?
 
#10 ·
The cars here don't have to meet US or Euro emissions requirements, so they are not optimizing fuel/air ratios for pollution control. We rented a Toyota Camry 4cyl in Peru and took it to 16,000 feet without a problem. On the other hand, they must be driving these cats at above 12,000 feet in Colorado, so there has to be a solution that doesn't cost thousands of dollars.
 
#15 ·
The cars here don't have to meet US or Euro emissions requirements, so they are not optimizing fuel/air ratios for pollution control. We rented a Toyota Camry 4cyl in Peru and took it to 16,000 feet without a problem. On the other hand, they must be driving these cars at above 12,000 feet in Colorado, so there has to be a solution that doesn't cost thousands of dollars.
I agree with RAVN4RED, something here does not compute. Are you saying that a supposed non-polution controlled Toyota runs better than your (I assume) US bought one at high altitude?

Of course I don't know for sure but I can't believe that all gasoline cars & trucks worldwide aren't electronic fuel injected, and with O2 sensor feedback systems, running at 14.7:1 air/fuel ratio regardless of air density. Other pollution controls such as vapor recovery may vary but 14.7 wouldn't. And to maintain it the ECU doesn't have to relearn anything it simply works off the O2 sensors which aren't affected by ANYTHING - except leaded gas. If they're still using that somewhere in the world their cars can't be tightly AFR controlled, or if you ran leaded gas in yours who knows what would result.
 
#11 ·
I think you've got something else going on. Poking around the forum, complaints from 4-bangers in Colorado were about not being able to bust up the highest hills around 11K-feet at freeway + 75 mph. But everyone was able to at least 'muster 50 mph' and others said 65 mph no problem on the same hill (Eisenhower I-70).


So if you are at 12K and can't even move, something else is way wrong. The ECU is supposed to learn as it climbs. Is there a regional Toyota center in Central America might know about the idle reset that was suggested?


On sidebar note, at 12K-feet and above, the FAA requires pilots in non-pressurized aircraft to wear oxygen masks. Meanwhile, the passengers get very sleepy...
#
 
  • Like
Reactions: Dr. Dyno
#12 ·
Thanks for the thoughts. The hills here are a lot steeper than they are in the US. The car does suffer from a complete loss of power, probably at around 12,500 feet. At that altitude it simply can't go up a hill. I will take it to another dealer before we get to altitudes above 11,000 feet again.

It really sucks to have spent a couple of years planning and saving for a trip and to have bought a car specifically for that trip and then find out that the car can't do it.
 
#13 ·
#14 ·
Interesting. This would seem to support the notion that there is something wrong with my car, although that author and I may have different perspectives on performance. I see another trip to a dealer in my future. In any event, I'm going to try to track down the officially sanctioned idle relearn procedure and run that. I took the car to 11,000 feet today. I dropped it into first gear at about 9,0000 and it did OK. Under the heading of full disclosure, the hill it refused at 12,000 feet was off-road and a little (not horribly) steep. So the car was undoubtedly in AWD mode.
 
#16 ·
What I'm thinking is that the ECU is mapped to meet emissions requirements and, probably, maximize mileage, perhaps at the expense of other performance characteristics. But I really don't know. In Guatemala, at first the dealer told me that they could remap the ECU to fix the problem. Then they told me since it was a US car they could not. I don't know if it was an equipment issue on their side or whether the ECU fuel mapping simply can't be changed on some models. I did call a Toyota technician at a dealer in the US who indicated that, as far as he knew, the ECU could not be remapped. He did not suggest that there was something wrong with my vehicle and, like the Guatemala dealer, thought that idle relearn might help.

Really I'm just trying to find a solution to a (for us) serous vehicle problem. I'm open to all suggestions and I'll definitely take the car to a dealer before we hit the higher altitudes in Ecuador and Peru.

I'm still looking for the proper idle relearn procedure as well, including the suggested altitude for performing it.

I appreciate everyone's help.
 
#17 ·
It appears to me no one is actually diagnosing the issue. They are all in the try-this mode which no more help than we can give from the forum. You'll need to find a shop or better yet a dyno where they can read the air/fuel ratio when the drastic power loss (which is apparently way more than Tex's altitude formula can account for) occurs. It's either going way rich or lean or there's another problem but you need solid data to find a solution. If it was mine I'd have an air/fuel ratio meter that uses a wide-band O2 sensor installed. If I saw it going richer than 12:1 or leaner than 15:1 I'd have a clue what to do next.
 
#19 ·
Some motorcycle dynos are installed in sound-proof and relatively small rooms. If ventilation isn't done properly altitude can be simulated by mistake. The test is to open the door an inch and turn on the ventilation. If the door moves, and I've seen them slam shut, they're simulating altitude. I don't know if the same is true for car dynos but the ones I've seen are typically in a large shop not their own room. So the dyno itself might have to be at least some altitude. I'd guess you'd start seeing the issue at 6,000 feet or so.

Another factor is at full throttle the system runs open loop on the ECU's look-up tables or maps not on the O2 sensors. The inputs for the tables are the temperature and barometric sensors. If one of them is defective but not enough to set a code the system could go too lean at full throttle but run fine at less than full throttle in closed loop on the O2 sensors.

If you find someone who understands my last three posts you may get some results. My bet is no one you've talked to yet would.
 
#20 ·
Thanks. This is very helpful. It's not just a full throttle problem, as it's the lack of oomph that's causing me to put the pedal to the floor. I imagine that a faulty-but-not-yet-failed sensor is a difficult thing to diagnose. I'm going to see if I can talk to a Toyota tech in Colorado. And maybe stop in Cali for some diagnostics. Colombia has a bit of a gearhead culture, so I should be able to find a competent shop.
 
#21 ·
This is what my independent Japanese mechanic pulled from Toyota direct to reset your idle. It worked for me, although the butterfly never completely shut on mine, the procedure still made an improvement. Worth a try... I'm envious of your journey and experiences, best of luck to you!

It is always important to use a Memory saver when doing a battery disconnect on newer vehicles. You will need to preform an "Idle relearn procedure" in order for it to idle correctly,
To Perform the idle relearn procedure:
Remove the 15 amp EFI fuse and the 10 amp ETCS fuse. Remove the boot from the throttle body and clean the throttle plates. Make sure the throttle plates closed completely. Reinstall the fuses. Turn the ignition switch to the on position making sure the throttle plates are closed when the key is turned on. Install the intake air boot and THEN start the vehicle. Allow the vehicle to idle until the cooling fans come on.

NOTE: It is very common for the computer to lose the idle memory when the battery is disconnected. If there is excess carbon buildup in the throttle body, this causes the low/rough idle speed.

It took a long time for my fans to kick on and my trucklett was pre-warmed. So grab a beer and wait, they will go on.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top