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inconsistent power in 1800 to 2400 rpm range

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Old 12-22-2009, 09:15 PM   #1
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inconsistent power in 1800 to 2400 rpm range

Hi - hoping someone can shed some light on this before I push the truck off a cliff...

2008 Tacoma 4 cyl 5 speed, 2wd access cab has approx 4,000 miles - bought it with 2,100 miles and its done this ever since:

Feels like lugging or slight drop in power during normal traffic-type acceleration in 1800 to 2400 range. Occasionally, with slight increase in pedal pressure normal power returns but more often I need to get past 2400 to get any power back.

Dealer techs say they test drove and found no codes, so it must be me

Feels like its starving for fuel due to lean mixture.

Any thoughts appreciated!
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Old 12-23-2009, 09:21 AM   #3
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Thanks for the reply

I'm thinking there may be some investigation required in the "fly-by-wire" comment. Being an old Chevy big block gear head, this problem reminds me of sticking carb linkage. ANy advice on adjustment or testing of the fuel-pedal system?

As far as pushing the pedal harder, there are no problems when getting up to speed, under hard acceleration ie. - 1st, 2nd and 3rd gears - its only when you are up to cruising speed in 4th and 5th that you notice this problem.

Kinda defeats the purpose of cruising and makes your speeds erratic if you have to accelerate hard just to get through the "bog zone". Interesting to note also that on occasion, while keeping constant pedal pressure, I'll feel the power return - thus the inconsistent power.

Since most of the time I'm cruising at 55 - 65 mph, I'm in the 1800-2400 rpm range so its a REAL pain in the ass.

Much thanks again!
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Old 12-23-2009, 09:47 AM   #4
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take it back and have the tech ride with you, everybody drives differantly so he may not be able to duplicate the said issue
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Old 12-23-2009, 04:45 PM   #5
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My o9 reg. cab with 5-speed does the same thing. Most definately feels like a lean spot.
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Old 12-24-2009, 10:05 AM   #6
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Thanks for the feedback you guys.

I found a service dude at Toyota who will ride with me after the holidays. He warned me that if there are no codes - they cannot help. (Well that wont stop them helping themselves to some more charges I'm sure).

Although I regret that you are having the same "lean spot", I gotta admit that it feels good to know I'm not alone. I asked the Toyota techs about dialing it in for getting a richer mixture and they just laughed at me - literally - they said that their corporate lords forbid them from adjusting anything that affects emissions.

I'll definately stay in touch when I get more info.

Merry Christmas!
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Old 12-24-2009, 01:20 PM   #7
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I haven't really noticed a "lean spot" like that in mine, but I'll pay closer attention to that RPM range next time I drive it. I wonder if it has anything to do with the VVTi? Maybe it switches valve timing at that point? Just a wild guess.
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Old 12-24-2009, 07:11 PM   #8
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overdrive

think i know what you are talking about. One thing on this truck that bugs the crap out of me is that it seems to love overdrive. Next time you are accelerating at a normal pace watch and it shifts to 4th, it almost immediately goes to over drive, and does not like to come out of it. Next time you believe that you are having a "lugging" condition press the throttle a little and give it some time. it might be at and area where the vvti and the transmission are kinda hunting. if traffic allows i try not to see much over 2200 rpm, and when it hits 4th it goes right to od, i just have to give it a sec and its fine, i don't know if the vvti adjust or what. one thing to remember is that in my opinion there is a rather large hp/tq split on this engine. hope this helps
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Old 12-26-2009, 10:57 AM   #10
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The truck starts making some power at around the 2200 rpm you have described. Maybe you are just feeling the truck getting into it's powerband?
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Old 12-26-2009, 11:12 AM   #11
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Get an urd maf calibrator to fix the lean spot its 250
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Old 12-30-2009, 04:31 AM   #12
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An update on the original post:

Went back to the dealer and took the service manager out for a spin - of course he couldn't feel this problem, but at least he didn't try to tell me it was just me. He promised to do some investigation into the problem and get back to me. We'll see.

Just when I was leaving I spotted a 2010 on the lot with the ultra rare 4cyl 5 speed combination. We took that thing for a comparison drive and although it was too short of a drive to be 100% sure - I'll be dipped in dog-crap - that truck seemed to do the same thing as mine does - sluggish and inconsistent power in the 1500-2500 range.

At this stage, I'm almost hoping its a universal problem - better drive that 2010 again and make sure...

By the way, on the subject of a "lean-spot" the service manager suggested that Toyota has received federal regulatory approval of the truck's emission system "calibration" and they cannot try to make an adjustment on mine without getting federal approval to make the same adjustment on all similar trucks. He suggested that the road test in the 2010 unit would be an apples-to-aardvarks comparison since the approved emissions "calibration" would be different from year to year.

He said any after-market chip or computer upgrade would void the warranty - especially the emissions systems warranty.

He also suggested that maybe the engine computer does not read the 5 speed trans very well - he suggested virtually all of the 4 cyls are autos.

So the bottom line at this stage is they don't deny there is a problem, they just can't feel it and they've never heard of it.

At this point I'm into the truck for over $23,000 Cdn (which is still almost $9,000 less than the the cost of the same equipped 2010 unit) but I just dont want to be blowin' more dough on what is basically at 5,003 miles a brand new truck.

So where to next? Unless I can figure a way to improve the thing without affecting warranty - I'm selling my 2008 Taco with 5,003 original miles and will buy back my 1991 extra cab that served me so well for almost 300,000...
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Old 12-30-2009, 05:06 PM   #14
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the aftermarket engine management will only void the warranty if they know you have it, get the harness and no need to plice and if you go in for waranty work or something take it off, then put it back on after
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Old 12-30-2009, 05:57 PM   #15
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Another update:

Found a super clean local low-mile 1998 Taco 2wd 4cyl with 5 speed and this truck does not have the "problem" my 2008 has - so I bought it.

Problem solved - now to sell the 2008.....

I guess I'm too old school and just not ready yet to live with these built-in issues. Thanks for all your help guys and gals and doggies!

Cheers

Dave
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Old 01-04-2010, 10:17 AM   #16
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FWIW no such flat spot in my '09 4 cylinder 5 speed PR.

Not a powerhouse in that rpm range, but it runs through it smoothly, and will pull 5th up from the low revs on level ground if I'm not in a hurry.
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Old 01-04-2010, 11:13 AM   #17
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Thanks for the comment - I wish I could have that smooth transition - esp. since its the range I spend most of my driving time in.

Dave
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Old 01-04-2010, 12:53 PM   #18
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As a side note looking at the dyno on another thread it seems the power lies in the upper RPM range on the I4 (I do understand the inconsistant fell though). I usually shift 3k in 1st and 2nd to get moving then normal 2k-2500 for the rest of gears. Works for me.
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Old 01-04-2010, 02:01 PM   #19
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That's the shift range for me as well.

There's no problems when I'm going for power in the higher rpm ranges, it just when I'm cruising in 4th and 5th in the 1800-2400 range is when this typically presents itself.

This is when the throttle pressure is both light and constant - thus its very noticeable.

Cheers

Dave
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Old 01-04-2010, 04:15 PM   #20
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it's prolly some kind of gas saving electronic thing...these trucks are drive by wire...which means the gas pedal is electric...not a wire going to a throttle body like older vehicles...just have to play around with the pedal pressure with your foot...press harder or smoother or something...i dunno it's tricky...lol
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