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Discussion Starter · #1 ·
My 2nd hand 2001 Sienna XLE seems to lack power in climbing hills always. It has gotten 120k miles. Runs great on flat highway and can go at 80+ mph without much effort on the pedal. It does not burn oil. Never overheat. Never got a code. In fact it runs perfectly in my opinion, except when it needs to climb a longer hill. It does not take a steep climb, just a common freeway slope will slow it down significantly. Every time the engine RPM will be slowed to around 2k at 40 to 45 mph. More pedal pressure will do nothing. Disable over drive will increase engine rpm but the speed remains almost the same. Only if I shift one gear up and press the pedal hard it will increase speed a little above 50 mph.

Comparing most other cars, vans, suvs and even trucks my Sienna is a dog on the hills really. I have had this car for 5 years and I tolerate the poor hill climbing all those years until recently when I drove it to Yosemite National Park. It was truly as slow as a dog. From time to time I found many (too many) cars were behind me and I could not speed up.

Is it the way it should be or is there anything I should do? I plan to replace the spark plugs soon. They were probably never replaced by the previous owner. The previous owner had to move overseas so it was forced to sell (to me). So it wasn't a problematic car before I got it.

I would like to know if that is the way it is supposed to be or there is something definitely wrong. If so what's your suggestions. Thanks a lot for all advices.
 

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Not sure if spark plugs would fail under increased load like that, but definitely check your air filter.

How is your overall fuel economy?

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Discussion Starter · #3 ·
The air filter was replaced but it did not improve the car's power in climbing hills. The fuel economy isn't great. It gets about 20 mpg overall city/highway driving. What puzzles me is it has power when driving on flat road. It has reasonable accelerating power. Takes light pedal driving in the city. A little more on the freeway naturally but not too much. It is really like a normal minivan except when climbing hills. It really slows down and feels powerless going up.
 

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Discussion Starter · #4 ·
I forgot to mention, The Sienna usually wasn't loaded at all. It usually just have two adult in it only.
 

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Here is a thought. If you are on the freeway, flat, going 70-80mph, and you floor it, do you have more power still, or is that as powerful as it gets? What I'm getting at is that maybe it has plenty of speed for around town and even getting up to 70-80, let's say that's 65% of engine capacity. Maybe it's lacking that last 35%, and you don't notice it until you go up hills, whether slight hills at 70-80mph, or steeper hills at 40-50mph. You say it acts normally until this scenario. Put another way, I'm not proposing that the engine is weaker overall, just that it is missing the top end of its power range (for some reason).

I don't know what the cause might be, but at least this might help you in troubleshooting. What happens if you floor it at 70-80mph on flat ground? Does it still have power left, or is that about it?
 

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I believe this is pretty normal, what kind of incline are we talking about? I am assuming Yosemite would have some pretty steep hills. I never been there but I know that my 02 has no issues with pick up at all on flatland, I can easily accelerate to 90 mph (don't really dare to go much more beyond that) but on hills it different. I have issues accelerating beyond 40-45 mph in remote areas of Southern Ohio, WV, and VA but these are pretty long steeper climbs that I am referring to. The vehicle is 4000lbs without passenger and gears and the motor is only 210hp.
 

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I've been up many times in my 98 Sienna on mountain highways (where it was so steep that semi-trailers could only crawl at about 30 km/h) and have had no problems going at 80+ km/h with a full load. I had an old GM car before that drove normally until I went up a hill. It would slow way down on a big hill even if you floored it. Turned out it had a partially plugged catalytic converter. I don't know if something like that would throw a code in a Sienna.
 

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Discussion Starter · #9 ·
Here is a thought. If you are on the freeway, flat, going 70-80mph, and you floor it, do you have more power still, or is that as powerful as it gets? What I'm getting at is that maybe it has plenty of speed for around town and even getting up to 70-80, let's say that's 65% of engine capacity. Maybe it's lacking that last 35%, and you don't notice it until you go up hills, whether slight hills at 70-80mph, or steeper hills at 40-50mph. You say it acts normally until this scenario. Put another way, I'm not proposing that the engine is weaker overall, just that it is missing the top end of its power range (for some reason).

I don't know what the cause might be, but at least this might help you in troubleshooting. What happens if you floor it at 70-80mph on flat ground? Does it still have power left, or is that about it?
Thanks for the reply. Great question, I can drive at 80 - 85 mph on flat freeway without hard pedal. I am sure I could go up to 90 or even higher if I floor the pedal. The acceleration on flat road is pretty responsive, not as fast as small sedans but due to the Sienna's weight. It is only when climbing longer hills that the speed will drop to 50 or even slower.

If the car is going at 80 mph on flat freeway and I floor the pedal it will speed up reasonably quick. I am sure it can go up to 90 although I never tried it. So it does have that last 30% or 35% of power there. What I don't understand is why it can not climb hills at least at 65 mph.
 

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Discussion Starter · #10 ·
OK, then, ... my second-favorite item to check for low-power situations would be the FUEL filter.

There were suggestions to check acceleration on the flats, so try that. Get going about 50 mph, then put the pedal to the floor to see what happens.

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I have been wondering if the fuel filter is the culprit. I will replace it and see what happens. By the way, I have tried to clean the air mass sensor and the throttle body flaps. It made no difference. The car has 110k miles on it.
 

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Discussion Starter · #11 ·
I've been up many times in my 98 Sienna on mountain highways (where it was so steep that semi-trailers could only crawl at about 30 km/h) and have had no problems going at 80+ km/h with a full load. I had an old GM car before that drove normally until I went up a hill. It would slow way down on a big hill even if you floored it. Turned out it had a partially plugged catalytic converter. I don't know if something like that would throw a code in a Sienna.
That's incredible to go at 80+ mph on steep hills. Are you sure about that?
 
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