So... my truck has been running like _CRAP_ for the last couple of weeks. Idle is fine, VERY erratic acceleration, VERY lean A/FR (16:1 in closed loop), NASTY NASTY spitting at WOT.

Depending on how you looked at it, and which symptom you got (too) focused on, you could make a case for it to be any of "the three" - spark, fuel or air. ugh.

I could "cure" the leanout by cranking up the piggyback, but the ECU would catch it and force it back to where it "thought" it should be. This is a weird aside btw... With the A/FR reading 16:1, the short & long term fuel trims were hovering around _zero_. The ECU thought it was doing a FINE job. * very weird *

I ran without the air filter for a couple of miles - it helped, but I think only 'cause the ECU saw a deluge of air flow, so it piled on the fuel.

Went through the electrical side.... all plugs firing, all injectors firing.

argh... then it hit me...

My son came to visit for a couple of weeks and we spent some time working on the truck. At one point we had the S/C off, and I figured we'd clean the TB while it was off and accessible. "Spray it in there Zack!" was the battle cry I gave my son while he had the intake cleaner in his hand. "Give it a good soaking!" "Yeah, see all that crud pour out?"

Ahh... 20/20 hindsight.

Now, I'd done this a ton of times without an issue, and even with all the time I've told people here to not spray too liberally, I would have never thought...

And then, when people have had symptoms very similar to what I've been seeing, I say "Check the TPS!", but certainly this would never be my issue.


So... I got my new TPS from Strap22 last night - I pulled the TB and replaced it in about 20 minutes. Jumped in the truck, spun the key, headed off to a long hill nearby....

fixed.

The truck is running like a top. WOOHOO!


So, lesson learned (Listen to your own preaching!) and some knowledge gained - it's clear that the ECU gives more priority to the TPS than the O2 sensor when figuring how much fuel to spit into a cylinder. weird.

Side note... the issue here is that if you happen to soak the TPS while you're cleaning your TB, things can go south. The element and/or wiper in the TPS can get crudded up and end up becoming very non-conductive. That translates to the ECU having NO idea where the throttle is, thus not know what to do for fuel delivery, then ending up in symptoms like above.

 

Well, we're just happy it works again, and that you learned a little lesson mark...

 

Pure Triumph

and I have written that one down...

 

yep, the o2 sensor doesnt react nearly fast enough for the ECU to give it priority

 

You got skillz Mark.

Question: Is it possible that since the SMT bases a lot of its "corrections" on throttle input, that it was going whacky because it essentially didn't know "where" it was...or simply that it was making fuel and timing corrections at the wrong part of the matrix?

I hope that made sense...

 

Yeah, that's something else that comes to me as hindsight. sigh.


Take the blue pill!

Actually, I figured you'd ask about this, and the answer is... I don't use TPS for that deflection input - I use the MAF. It gives me the ability to tune for what the engine is doing versus what it "should be" doing.

 

Brilliant!

sorry is this has already been covered but, where is the TPS in relation to the TB? Can I only see it if the TB is off?

 

On a 3.4, if you're standing on the passenger side of the engine bay, looking at the TB, then there is piece that is directly opposite the bellcranks where the throttle, kickdown & cruise control cables attach. Mine is black and has a 4 wire electrical connection coming off of it - that's the TPS.

It's held on by two philips screws, and if you have a shorty #2 philips, you can get it off without pulling the TB. BUT BE CAREFUL - the heads on the screws are soft, and if the screw is oxidized at all, you run the risk of stripping the heads out. I started to strip a head, which is what prompted me to pull the TB so I could get cleaner leverage on them.

When you put it back on, you'll need to note how the "flat" of the butterfly shaft fits into the TPS. The shaft will have a slight spring loading on it, so it will turn about 5* when you pull out the TPS. This is another reason to pull the TB to do this - it's MUCH easier to see what has to happen to get it back on with the TB sitting on the ground.

 

I really need to replace mine. Just haven't gotten around to it yet. I get a TPS CEL whenever I have the diagnostics port jumped and my RPMs around 2700. It pings like crazy right around there too.

Thanks for giving me more reason to get on this!

 

"twinotter"... are you a pilot or do you jump? (or both?!)

 

Neither, I'm just an Aviation buff and the twinotter is an awesome plane.
They used to fly one right over our trees from a little grass airstrip down the road. So cool.

I have been to ground school, but I can't afford the actual flight time.

Daniel

 

Right on... yeah, it's an awesome plane. A HUGE workhorse that's configurable to do just about anything.

{hijack off} wait... this is my own thread!

 

What is the approximate cost for a TPS?

I get similar symptoms from time to time and checked my MAF. It's pratcally brand new (been replaced in the last 30k mi).

 

If I remember right, I paid about $65 for mine from the dealership. That is with a discount though--not sure what normal price is. Should be less that $100.

 

$37.41 plus shipping via Strap22:

http://www.trademotion.com/partlocat...?siteid=214074

http://www.trademotion.com/partlocat...del=4%2Drunner

 

Excellent, thank you.

 

Wow, I guess a 3rd gen's TPS is a lot cheaper. My bad.

 

Well, it could have also been the source...

Strap22 is the Parts Dude at a Toyota dealership in Texas. He has permission to sell outside of the dealership at discount prices, so the price I quoted above (and as shown on the website) is below the normal dealer price. He shows a "$54.10 MSRP" for a TPS.

 

Just replaced mine today at $95, Its like night and day, For the life of me I cant think when it started going bad with no CEL, I just had to start clutching more and more to get the R's up and go.
(For those old enough, It was like a Carb'ed engien with no excelleratorpump)

I tested it 2 mo ago and it was fine and I pulled the plug on it and got the CEL, But I figued it out and checked it again, Yup , Vcc was bad but the ECU detected IDL and VTA to E2 was ok and thought it was fine.
Remember peole, Check the whole TPS for problems.

 

I've got a 95' Toyota Tacoma 2.7 4 cyl 4X4 with a rough idling problem. I took her in to a Toyota mechanic and got soaked $118 plus. The Tech worked on it vigorously for about an 1 1/2 plus he threw in some clamps on some vacuum hoses that i was kind suspicios of. Replaced on of the pcv valves...cleaned the Throttle Body Unit...Cleaned the MAF sensor. Runs fine when moving, it's the stop at lights,when put in reverse or drive that it starts to make the Steering wheel vibrate...real annoying. Acts like she wants to stall sometimes, give her a little gas, clears right up.
I've also replaced #1 O2 sensor,new plugs,new muffler and Catalytic converter. (after market) Mechanic who installed muffler did a poor attempt at welding on pipe. Could that leak be the problem? Tech from Toyota seemed bothered that after marked Cat and Muffler that was installed.
Last but not least...the longer she idles....the more she shakes! Can someone please help. I really like this truck and don't wanna upgrade to new.

Thanks,
Kevin