99BlackRunner

Hey guys & gals, hope i got this in the right place, it pertains to the 3.4 liter v6. Today I was late for work and really had to get into my 4runner to pass a few people. After getting into it hard a few times i noticed that it did not want to downshift at highway speeds. Then a few miles from work I pulled up to a stop sign and it idled at real low rpms and then cut off. Now the idling problem has come up with my past two 3.4 liter taco's but not the downshifting problem as they were both manuals and my 4runner is an automatic. On the way home it started rough idling and not downshifting again. I'm really hoping this is a fuel delivery problem and not a transmission problem. Any ideas? I really hate going to mechanics without any ideas, most around here are dirty as hell.

J2F42C

Any CELs thrown to diagnose this problem?

If none, then I'd ask if you have ever cleaned the IAC under the TB before? If not, do it by using the search engine, which should give you more than enough information.

Also, how is the transmission fluid holding up?

Kerby J

check to make sure that the trany fluid doesnt look like a strawberry milkshake bc if it does dont drive any more and search strawberry milkshake

96743runner

yeah x2 on checking for milkshake

99BlackRunner

No strawberry milkshake and tranny fluid was good. CEL was on but it's always on due to an o2 sensor, had it checked and it reads that the Throttle Position Sensor is bad(prolly should have started there, duh). I picked that up and am going to change it now. Definately good to know about the strawberry milkshake though, would hate to have learned about it after it happened. Thanks guys!

99BlackRunner

Okay i replaced the throttle positioning sensor on the throttle body and it did not solve the problem. I went back to Advance Auto and have them hook it back up to clear it out and check it again and it threw the same code; P0121-Throttle Position Sensor/switch A circuit. There gona do a defective exchange on the TPS but one of the guys claimed that there was another sensor down around the pedal that could be the problem, but he couldn't find it in his system and claimed that i would have to get it at the stealership. Ive searched around the net and can't find anything about a second sensor. Anybody know if the second sensor exist? BTW, the other codes thrown were P0171-sysem to lean, P0125-Insufficient coolant temperature for closed loop fuel control, and P1133-o2 sensor heater control circuit (bank 2 Sensor 1).

J2F42C

Why haven't you fixed the O2 sensor before? A $65 Denso more than likely will do you well. http://www.densoaftermarket.com/catalog/

PO125 code:
http://www.ncttora.com/fsm/1996/SIL/...e/cip0125o.pdf

Does your 4 runner have CA emissions? Then it may be a faulty A/F sensor.

Start with the cheap stuff. Clean your MAF (the two little wires) with some CRC MAF cleaner for ~$7 if you have not done it yet.

gdutch

I had problems with downshifting at highway speeds when my engine was having misfires. If you aren't running at full power, you will likely run into the same problem. I'd clean the MAF and the interior of the throttle body as well, replace the O2 sensor, and see what happens from there.

99BlackRunner

Okay tonight i'm gona clean the MAF with CRC MAF cleaner and check the old and new TPS with an ohm meter and go from there, the guy at the parts house has seen more than a few faulty right out of the box. Will try to dig into the throttle body and o2 sensor this weekend when i've got more time. Again thanks for all the info, that repair manual on ncttora is awesome.

brian2sun

Your code "P0121-Throttle Position Sensor/switch A circuit" would indicate to me a connection (wiring) problem somewhere between the TPS and the ECM.

J2F42C

When you clean the MAF, make sure to spray the two tiny wires located down the tube, not just the air temp sensor at the guys did in this video:

http://www.youtube.com/watch?v=qiEde...eature=related

Once the two wires are cleaned, you can look down the tube and you should be able to see them without the aid of a flashlight. Don't touch them!

CRC video on why to only use MAF cleaner when cleaning a MAF:

http://www.youtube.com/watch?v=vPT8r...eature=related

Beto

I hate to bring in another variable here, but it sounds like it might be related to electrical transmission control....if the lock-up clutch solenoid does not disengage, it'll cause stalling out. The reason I think of this is because it also won't downshift - they might be related in a round about way.

The lockup clutch should only engage when you are in overdrive, at highway speeds, not accelerating hard. It kicks in to lock the input shaft of the transmission to the engine instead of letting the torque converter slip under these conditions - saves fuel and your RPM's drop by about 400-500 when it happens. It is not designed to handle much of a load, so if you put the pedal to the floor or kick out the overdrive, it is supposed to unlock - also the reason that overdrive is not recommended when towing -- too much stress on the lockup clutch.

If it doesn't unlock, your engine will stall when stopped at an idle, because it is not allowing the torque converter to slip (and your engine to keep turning).

It could be a speed sensor, but I really think you should pull all the codes before we speculate further...

99BlackRunner

I'm looking at the directions for inspecting the TPS now:
When it says "apply vacuum to the throttle opener" does that literally mean hook up a shop vac to this hose? Also, i don't have any .32 or .54mm feeler gauges to insert between throttle stop screw and stop lever, could i substitute something there?
Beto, thanks for the electrical transmission control idea, i'll have to check into that as well

Beto

I don't want you to read anything into the following, but "apply vacuum" means to expose that line to vacuum pressure - the service techs have a little hand-held vacuum pump for that, you can develop enough vacuum by sucking on the hose, and putting your tongue on the end, then sucking a little more, tongue on the end --- think really, really, really thick milkshake. When you have developed full manifold vacuum (that which is present at idle - about 20 to 25" of mercury) the hose stuck on the end of your tongue will kind of burn a little as it develops a tongue hickey.

Your feeler gauge issue - the cover of a matchbook is about 0.012", double it up, and you have about 0.024". This equals 0.31mm and 0.62mm - hope it helps.

99BlackRunner

Thanks for clearing that up Beto, i'll just be sure to close the garage door before i apply vacuum.

brian2sun

The code says it's the TPS circuit. I would start there. You have a bad wire somewhere.

J2F42C

I hope the MAF cleaning went well. I do not think it is the silver bullet to your problem, but a good cleaning will not hurt it.

More reading:

PO 121:http://www.ncttora.com/FSM/2003/Repa...fe/cip0121.pdf

Download the rest of the manual from here:

http://www.ncttora.com/fsm/

99BlackRunner

MAF cleaning did go well, super easy with the write-ups available. Will definitely be doing that on a semi-regular basis now.
As far as it possibly being a bad wire somewhere, i have no idea how to go about finding that unless it's a visible bad spot. May have to seek help of a mechanic if thats the case. Only experience i have wiring things is on a boat witch is extremely basic. That sound's probable at this point though because the problem is no longer constant. It was doing it on sunday evening and all of a sudden monday morning it was fine and has been so since, will have to wait and see.

Beto

Do you have drive by wire? (two ways to know - when you push the throttle pedal to the floor with the key OFF, does the butterfly in the throttle body only open part way? If so, it is DBW. 2nd, do you have a transmission kick-down cable on the TB? If so, it is NOT DBW.

I'm more familiar with drive by wire, the code you are pulling is the sensor on the TB that the throttle wire pulls when you push the pedal - behind the sensor is a motor controlled by the ECU that actually opens the butterfly.

I can't attach the .pdf because its a kB too large, but check the factory service manual for code P0120 - it explains the wiring and wire colors, also test procedures. Much more in-depth than P0121 documentation. The code P0121 leads me to believe that the sensor is bad, not just a loose wire, b/c a loose wire (complete failure) would trip P0120. Anyways, you have a place to start...

brian2sun

Yes, the way the code reads, it could be the sensor itself or the wiring, but he said the TPS is new so it's unlikely that he got a defective one. For the wiring, it's not going to be easy because that wire goes into a loom along with a hundred other wires so I would look at the color of it, check the connections on the TPS side and then check the conn. at the ECM side. Hopefuly it's not somewhere along the wire inside of the loom, I doubt it is though. The sensor