# Tundra bogs down under load, but not when using cruise control **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** transmissions, diagnostics, engines, toyota, tundra\ **Created:** [August 10, 2016, 4:30pm UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447 "2016-08-10T16:30:33Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![buffalogirlfarms](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/buffalogirlfarms/32/4766_2.png) [@buffalogirlfarms](https://community.cartalk.com/u/buffalogirlfarms)\ **Post date:** [August 10, 2016, 4:30pm UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/1 "2016-08-10T16:30:33Z")
My 01 tundra can bog down under load - going up a long hill or towing a trailer - with the speed and RPMs steadily dropping until it finally downshifts, and the RPMS shoot up to 4k or so, but I don’t regain much speed. This is without cruise control. If I have the cruise control on the problem does not occur. The truck slows, but in a normal way expected under the circumstances. The CEL is not on. No codes are being recorded. The Tranny fluid is full and smells fine. Ideas? ---
**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\ **Post date:** [August 10, 2016, 7:03pm UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/2 "2016-08-10T19:03:16Z")
I suspect it has to do with being in overdrive (torque converter lockup). Sounds like cruise control keeps it in overdrive vs manual control unlocks and downshifts more readily. This might be intentional. ---
**Author:** ![buffalogirlfarms](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/buffalogirlfarms/32/4766_2.png) [@buffalogirlfarms](https://community.cartalk.com/u/buffalogirlfarms)\ **Post date:** [August 11, 2016, 4:06am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/3 "2016-08-11T04:06:30Z")
I have tried turning the overdrive on and off to see if it makes a difference when I am not using cruise control, and it does not make a difference. One thing that does make a difference is ambient air temp. On hot days the problem is worse. I was wondering if some vacuum circuit gets bypassed when using cruise control. If a vacuum leak is bypassed. ?? ---
**Author:** ![TwinTurbo](https://avatars.discourse-cdn.com/v4/letter/t/8baadc/32.png) [@TwinTurbo](https://community.cartalk.com/u/TwinTurbo)\ **Post date:** [August 11, 2016, 4:57pm UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/4 "2016-08-11T16:57:15Z")
The Tow/Haul mode being on should actually make the problem a bit worse when you’re in control of the throttle. It prevents excessive hunting and purposely slows down the shifting. The adaptive cruise control might be more responsive to engine load. Engine load problems will usually be worse on hotter days, the air intake is less dense. Less oxygen, less fuel injected. What happens if you romp down on the gas pedal when you feel it starting to lag? Does it downshift sooner and perk up? ---
**Author:** ![buffalogirlfarms](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/buffalogirlfarms/32/4766_2.png) [@buffalogirlfarms](https://community.cartalk.com/u/buffalogirlfarms)\ **Post date:** [August 12, 2016, 3:27am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/5 "2016-08-12T03:27:50Z")
If I stomp on the gas when I first notice it bogging down it does not downshift and accelerate. It continues to bog. If I feather the pedal it can sometimes perk up… but not by downshifting, It just briefly gets power and accelerates “normally” before bogging down again. If I continue to feather the pedal it will sporadically accelerate, but not for long. ---
**Author:** ![TwinTurbo](https://avatars.discourse-cdn.com/v4/letter/t/8baadc/32.png) [@TwinTurbo](https://community.cartalk.com/u/TwinTurbo)\ **Post date:** [August 12, 2016, 2:08pm UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/6 "2016-08-12T14:08:09Z")
> If I stomp on the gas when I first notice it bogging down it does not > downshift and accelerate. Hmmm, that’s a tough one. Normally, I would say you have some fundamental driveability problem and start troubleshooting from that perspective but the fact that when using CC it doesn’t occur, that is a strange wrinkle… ---
**Author:** ![buffalogirlfarms](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/buffalogirlfarms/32/4766_2.png) [@buffalogirlfarms](https://community.cartalk.com/u/buffalogirlfarms)\ **Post date:** [August 12, 2016, 3:17pm UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/7 "2016-08-12T15:17:45Z")
I’m beginning to think that it is Dutch Elm Disease or Poltergeists. Thank you so much for your input. I appreciate your taking time to think about this with me! ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [August 14, 2016, 12:40am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/8 "2016-08-14T00:40:37Z")
Yeah, it could be Poltergeists … lol … That’s the ticket! hmm … let’s put on our thinking caps, how does the engine and transmission decide when to downshift? It seems like it must use from among these inputs to decide 1. engine rpm 2. transmission input rpm (should be close to number 1 above) 3. transmission selector lever position 4. transmission gear currently engaged (so it knows tranny output rpm) 5. MAF and/or MAP reading 6. throttle position sensor reading 7. vehicle speed Guessing the problem is something with all that. Since it goes away with the cruise engaged, and no codes come up, my first bet is the throttle position sensor is not reading accurately for some reason. Next up: the transmission gear selector position isn’t making it to the computer correctly. After that, the vehicle speed sensor is malfunctioning. ---
**Author:** ![NYBo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nybo/32/17281_2.png) [@NYBo](https://community.cartalk.com/u/NYBo)\ **Post date:** [August 14, 2016, 12:45am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/9 "2016-08-14T00:45:38Z")
Are the conditions truly the same except for cruise control? This sounds like classic fuel starvation from a clogged fuel filter or failing fuel pump. If you are using the throttle more aggressively than the cruise control does, that could explain the phenomenon; the cruise control may be a red herring. ---
**Author:** ![buffalogirlfarms](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/buffalogirlfarms/32/4766_2.png) [@buffalogirlfarms](https://community.cartalk.com/u/buffalogirlfarms)\ **Post date:** [August 14, 2016, 12:57am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/10 "2016-08-14T00:57:17Z")
Wow! That’s some deductive reasoning. But if none of those sensors are throwing a code, perhaps they are only malfunctioning intermittently. It sounds like this will take some serious attention by someone who a) cares and b) knows enough. Those two characteristics are hard to find in one mechanic! Thanks for the suggestions. It is great to have a list to start checking things off of! ---
**Author:** ![buffalogirlfarms](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/buffalogirlfarms/32/4766_2.png) [@buffalogirlfarms](https://community.cartalk.com/u/buffalogirlfarms)\ **Post date:** [August 14, 2016, 12:59am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/11 "2016-08-14T00:59:58Z")
Good point. As a matter of fact, I think I’m less aggressive on the accelerator than the cruise control, since I can see the hill ahead of me, and I start to accelerate before the cruise control would. Still, what will it hurt to slap on a new fuel filter? Perhaps a fuel pump is cheap enough to replace diagnostically, too. I’ll put those on my list. Thanks! ---
**Author:** ![buffalogirlfarms](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/buffalogirlfarms/32/4766_2.png) [@buffalogirlfarms](https://community.cartalk.com/u/buffalogirlfarms)\ **Post date:** [August 14, 2016, 1:03am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/12 "2016-08-14T01:03:23Z")
On re-reading your post, I realize that I am also at about 6,000 feet altitude. I wonder if the lower 02 density combined with the 220,000 miles on the engine are factors. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [August 17, 2016, 12:43am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/13 "2016-08-17T00:43:24Z")
You engine computer knows the altitude from its sensor readings, and adjusts the fuel injection amounts for the reduced O2 when at higher altitudes. At least it should do that. I wouldn’t assume that’s the problem unless the problem goes away when driving at lower altitudes. ---
**Author:** ![NYBo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nybo/32/17281_2.png) [@NYBo](https://community.cartalk.com/u/NYBo)\ **Post date:** [August 17, 2016, 12:59am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/14 "2016-08-17T00:59:54Z")
[quote=“GeorgeSanJose, post:13, topic:94447, full:true”] You engine computer knows the altitude from its sensor readings, and adjusts the fuel injection amounts for the reduced O2 when at higher altitudes. At least it should do that. I wouldn’t assume that’s the problem unless the problem goes away when driving at lower altitudes. [/quote]Regardless, normally-aspirated engines do lose power as altitude goes up. However, given how many miles are on the truck, the engine may be worn out. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [August 17, 2016, 1:18am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/15 "2016-08-17T01:18:46Z")
The problem might be with the throttle control actuator. [https://www.rockauto.com/en/moreinfo.php?pk=3769359&cc=1375365&jsn=358](https://www.rockauto.com/en/moreinfo.php?pk=3769359&cc=1375365&jsn=358) Or the throttle pedal position sensor. [http://www.carproblemzoo.com/toyota/tundra/2001/accelerator-pedal-sensor-problems.php](http://www.carproblemzoo.com/toyota/tundra/2001/accelerator-pedal-sensor-problems.php) [http://www.toyotaguru.us/sequoia-2001-repair/note-electronic-throttle-control-system-etcs-may-also-be-referred-to-as-electronic-throttle-control-systemintelligent-etcsi-or-etcsi.html](http://www.toyotaguru.us/sequoia-2001-repair/note-electronic-throttle-control-system-etcs-may-also-be-referred-to-as-electronic-throttle-control-systemintelligent-etcsi-or-etcsi.html) Tester ---
**Author:** ![buffalogirlfarms](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/buffalogirlfarms/32/4766_2.png) [@buffalogirlfarms](https://community.cartalk.com/u/buffalogirlfarms)\ **Post date:** [August 17, 2016, 1:38am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/16 "2016-08-17T01:38:02Z")
Thanks, Tester! These are some new ideas which seem probable… esp the throttle position sensor. The article you linked to on carproblemzoo says that a malfunction will trigger a code, and there aren’t any codes coming up, nor the check-engine light. That doesn’t mean there isn’t a malfunction, though. When the CEL comes on, I always check, and every time I’ve found an engine there, so I don’t really trust the CEL. :-)😊 ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [August 17, 2016, 2:30am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/17 "2016-08-17T02:30:40Z")
lol … that’s a good one OP! ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [August 17, 2016, 3:18am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/18 "2016-08-17T03:18:32Z")
The V-6 uses classic throttle operation, the V-8 has electronic throttle control. Which engine do you have? If the engine holds at 2500 RPMs at full throttle and won’t downshift I would manually downshift. ---
**Author:** ![buffalogirlfarms](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/buffalogirlfarms/32/4766_2.png) [@buffalogirlfarms](https://community.cartalk.com/u/buffalogirlfarms)\ **Post date:** [August 17, 2016, 11:59am UTC](https://community.cartalk.com/t/tundra-bogs-down-under-load-but-not-when-using-cruise-control/94447/19 "2016-08-17T11:59:19Z")
It’s a V6. When this happens, I’m usually trying to maintain highway speed. Even if it slows to 50mph, I don’t think I’d want to downshift. Would I?