Need help diagnosing 2012/4.0

Apologies if this is long winded (try my best to keep short). I also spent considerable time searching for other similar posts (so I wouldn't repeat), but although I found similar posts, nothing exactly as I have been having. My Taco is '12 w/ 4.0 4x4 SR5 Access Cab w/ no mods and 135k miles.

My problems started almost 3 months ago with the dreaded trip code/secondary air switch valve stuck. I opted to go the bypass kit route and through many calls and adding sensors to my kit, I was unable to make it work. Hewitt was great w/ customer service and agreed to accept a return (Kudos to them. A1 in my book). Anyway, I sourced a OEM switch valve, installed it and that prob solved. Added a breather filter to air pump and good to go. All in all, spent 3 plus weeks in and out of limp mode while trying to get the issue resolved (good thing I work really close to home)

Here's is where things started getting annoying AF. During and after the aforementioned repair, I noticed the following issues...

1. Shifting hesitation at lower speed shifts.
2. Slightly louder engine sound (almost not noticable to others).
3. subtle loss of power. (again, not noticable to others).
4. Clunk sound when reversing.

Remedies I have tried...

1. Reset throttle sensor (via the gas pedal trick). Seemed to help with shifting a little, but not eliminate.
2 & 3. Two different mechanics. 1st felt no noise or power probs and no codes. 2nd suggested motor mount replace which ended up having no effect on noise, shift or power loss.
4. Replaced entire driveshaft which was loose at center bearing. This eliminated the clunk but no effect on engine noise or power loss.

Since all this started, I have only driven on local roads at speeds under 40ish. However, last weekend I took a trip (30 mins to and 30 back on Hwy). Still had less power on the first leg, but got to speed (65) okay. On way home, way more loss of power and unable to maintain more than 50 on slight uphills and that with a downshift and pedal to the floor. No temp issues, no check lights, nothing to indicate there's a problem. Took it to have trans fluid replaced, and although needed (given my milage), did not help w/ ongoing issues. The mechanic then drove it on hwy and didn't experience the power loss. I Inquired to mechanic about a possible Cat problem, but they poopood that given no check lights and nothing showing on scan. So, finally I added a bottle of Cataclean yesterday, cause I don't know what else to do and am very frustrated.

So, in short, I still have louder engine w/ less power and shifting stumbles w/ no remedy in site.

Again, sorry for the length of this post. I hope someone can help.

BTW, I checked the gas cap, my plugs are newish and I change oil/filter religiously.

 

Great first post, an exemplar of the level of detail needed to try to start troubleshooting a problem intelligently. Welcome to TW forums!

 

Because of your notes about shifting hesitation + loss of power + louder engine noise it occurs to ask if the transmission fluid level has been checked. Later in your post you said that you had the trans. fluid replaced. Do you trust the shop that did that? If you have any doubts about the shop's competence / care, it wouldn't hurt to double-check the transmission fluid level using the appropriate protocol.

Here's an example of the proper procedure:
https://www.tacomaworld.com/threads/how-to-drain-refill-automatic-transmission.63851/

 

You've checked all of the ends of the vacuum hoses for splits?

Cleaned the MAF sensor?

At 135k miles, your fuel filter is quite saturated with contaminants. Wouldn't hurt to swap in a new good unit, or do a fuel pump & filter upgrade.

 

Thx. I do trust the shop I had fluid change done at. They even offered the three levels of fluid change. 1. simple drain and fill. 2. flush including rad lines. 3. pan off w/ flush and filter change.

 

Thx. I have not. I have a family mechanic do all routine service and is really good at checking things every time I bring in for oil change. Nonetheless, I thought about the MAF cleaning and fuel filter, but haven't done them given that all the probs happened during and after the air switch probs. I am not opposed to the items mentioned, but I've put so much into the problem already, the wallet is running lite (lol) and I would like to narrow down the possible remedies before spending more. That aside, thank you for the suggestions, and they will help a lot.

 

Might be prudent to seek out a diagnostic tech (this may have to be a dealer technician) to have a look at this. A knowledgeable tech can monitor some live data for anomalies in fueling, spark, timing, etc to see if they can narrow the possible causes of these issues. Throwing parts at it will get increasingly expensive with no certainty of actually reaching a solution. I know everyone likes to hate on the dealers, and certainly there are some deserving of that behavior, but there are also some that actually employee well-trained, knowledgeable technicians that are essential to getting to the root of a problem like this.

 

I 2nd the suggestion to check the trans level. Its not difficult once you master getting into temp check mode, and doesn't cost anything. MAF cleaning is also cheap and you can DIY.

Was the battery unplugged while any of the previous service was done? It can take a while to fully relearn, mixed highway and around town driving is best to relearn. If not, it would be best to unhook the batt. while you are cleaning the MAF to force a relearn with clean MAF readings.

Last thought, "look where the human was last". I cant really see how the SAIS could impact performance without setting any codes. But worth double checking to see if anything is obviously amiss.

 

Thanks Mike. I am considering this option. Although the Toyota dealer nearest me, I abhor. So it'll have to be nearest town, who I feel a tad better about (yes, I have a healthy distrust of dealerships as well. Lol). Would like to exhaust the options before going that route, hence my post here to all you fine people.

 

I second this now that you still are having issues. A good example I had with a similar situation was a cracked vacuum line. Looked just fine but doing live monitoring of certain engine values led us to a vacuum leak. Once we had the hose off it was indeed cracked through.

Good luck with a solution

 

Some budget code readers can monitor some live data values. You might try watching fuel trims while driving when the problem occurs - see if it's leaning out or going crazy rich. O2 sensor readings might also provide some useable feedback as well. The MAF values can also be checked pre and post cleaning to see if there is any noticeable change.

 

If you’re willing to download and setup TechStream, you could continue diagnosing yourself to avoid a dealership.

Do a google search on downloading and setting up TechStream.

 

Thanks. Yes the battery was disconnected numerous times during the SAIS/Bypass/Switch valve replace. I subsequently learned about the throttle sensor reset.
I have off today, so gonna go to parts store for some MAF cleaner and a new fuel filter. While at it, I will double check if the shop did indeed pull the overflow plug and ensure proper level at Op.Temp. May even clean the throttle body.

Edit: Just did a search for 2012 fuel filter location and discovered it's in the gas tank. Guess I won't be performing that job. Thanks Toyota.

 

Indeed, good alternative, Thx. My prob is not a lot of free time, not a lot of mechanical know how and less patience, lol. And I still have a new rad in box awaiting cooler weather to install and my family mechanic says, my struts need replacing. Anyone want an otherwise well maintained Taco? Hah.

 

Today's update...
I cleaned the MAF (which was fairly clean already). I checked the hoses within eyeshot and the hose going into connecting just below the throttle body had no spring clamp and just pulled off with no resistance. Not sure that's normal. However the hose itself was clean and no signs of cracks. I'll get a clamp for that tomorrow.
Also, forgot to add that I replaced the PCV valve during the previous troubles and since there wasn't a spring clamp before and the hose fit snugly, I refit the hose as it was. I decided to order a new PCV & hose from Toyota just in case and will install tomorrow. Although, I doubt that could be the cause of my probs. If by end of week I still have the issue, I will reluctantly call the D(St)ealership. Thanks for all of your input.

 

I doubt the PCV has anything at all to do with it.

Like some others have said, you’ll need the ability to see and log data as the truck is having the problem.

 

Yeah, I doubt it too. Just want to eliminate everything w/in reason before going to get a diagnostic.

I've got several grand in this this year alone...Brakes all around w/ rotors and calipers, fluids, rad, motor mounts, Switch valves. And none of it fun stuff like better shocks, rims, etc. Sucks.

Thx tho.

 

I’m wondering if it’s sucking air where the hose clamp is missing. But you said it fit tight so maybe not.

Battery posts can get oxidized, they should look silver, not dark grey or black. Still, a dragging alternator shouldn’t keep you from going more than 50.

I wonder if your brakes are dragging. You could jack up & spin the wheels. Or next time it happens check if there’s a tremendous amount of heat coming from the drums or rotors.

I know how frustrating some things can get. Since you admit to “not a lot of mechanical know how” you might be better off having someone diagnose it for you. Perhaps someone different than the 2 who already looked at it. I have enough knowledge to be dangerous and make it worse. Fortunately I have a local dude who’s good for when I don’t want to do it myself. Maybe you can find someone in the regional forums.

 

I picked up a new OEM PCV and hose w/ clamps and a clamp for the vacuum hose going into throttle body. Will install today.
The brakes should not be the prob as I just replaced the rear pads and front pads, rotors and calipers.
I was under the truck yesterday while it was idling and the sound is very close to what a small exhaust leak would sound like. But there were no leaks that I could see or hear. Def coming from front, near or in engine.
Going to sched a visit to dealer for end of week or next.
As for my mech "know how"...I'd say between a complete moron and a skilled mechanic, I'm somewhere in between. Lol. I'm like Nikki Lauder, bad brain and a great ass, I can feel what's wrong, just probably won't be able to fix it. Haha

 

As far as I recall there are only two hoses that attach to the throttle body itself (aluminum piece). Those are coolant lines