I'm out of ideas.

[Biologist]

I have a 1999 4Runner with about 250k miles. It runs really well except for one problem. On long hills it will start doing this engine miss or torque converter coming out of lockup thing. It feels like when the fuel pump on a car is going out and it just kinda slams and reconnects. I don't really see the tach needle move much though. But I am unsure if the engine is missing or the transmission is the problem. It does have a very slight miss occassionally idling but other than that the engine runs great, good power, good mpg. When it does the thing on the hill a few times it usually downshifts and the rpms increase and it runs fine for the rest of the hill. I'm trying to get it running perfectly so I can sell it. It is really frustrating. It throws no codes that I see on my code reader.

The things I have done already.-

1. Tried 87 and 91 octane. Tried many tanks of gas.

2. Tried Techron.

3. Replaced fuel filter.

4. Replaced fuel pump. Gas tank is clean as a whistle, no crud in it.

5. Bought used coilpack on ebay that was supposed to work. Switched out each of the three coilpacks. No difference.

6. Tightened intake manifold and looked for vacuum leaks. Replaced cracked hose going to intake manifold.

7. Spark plugs are new. Spark plug wires are new.

8. Drained and refilled with synthetic ATF.

9. Put in Dr. Tranny Shudder Fix and Lubeguard Red bottle that are supposed to work great from reading reviews.

10. Air filter is new.

11. Oil is new.

12. There was a problem with a failed injector #1 causing a different problem but I replaced it and that problem went away.

13. Cleaned mass air flow sensor.

14. Checked for gas leaks at injector O rings.

None of those things have made the problem go away. If you drive it for a long while (like a trip of >30 miles or so) it stops doing the hill thing pretty much, but when cold or for the first few miles it does it every single time. I can't with a clear conscience sell this to someone. Even if they didn't detect the problem in the test drive, it would be there. That is all I can think of that I have done now. Any help would be greatly appreciated!

 

[LookAtThatDog]

have you checked for valve cover gasket for leaks? Maybe its an issue with the overdrive?

 

[weekendclimber]

This sounds like similar symptoms that I was having. I cleaned my MAF and they persisted. Replaced the MAF with a new denso, problem solved. It might be worth testing to be sure before doing that, but this would be my guess. You getting any check engine lights?

 

[MONTYMTB]

7. Spark plugs are new. Spark plug wires are new.

Brand/model?

 

[cbr900boy]

Have you tried replacing the Throttle Position Sensor (TPS)? You can get a Toyota OEM on Amazon for around $40.


See below:

The 'Check Engine' Light is On
This is the first thing that you'll notice. The light is meant to tell you, the driver, that something is wrong with either a component of the car, or its sensor. It's always advisable to get your car checked out by a mechanic as early as possible if this light is on.

Bucking and Jerking/Hesitation while Accelerating
Another common symptom related to a bad TPS is the jerking of the car, especially when accelerating. Without proper inputs from the TPS, the on-board computer is unable to guide the engine to work at optimum levels.

Idle Surging
This problem usually comes in conjunction with the above one. Similar to getting jerks while accelerating, with a faulty TPS, the computer cannot tell if the throttle is fully shut when the car is idling.

Sudden Stalling of the Engine
This can happen anytime, without any kind of warning, while driving or idling. The TPS can give a bad input, prompting the engine to stall.

Sudden Surge in Speed While Driving on the Highway
This is a particularly hazardous situation. What usually happens is that at high speeds, the butterfly valve inside the throttle may close up, and if the driver pushes on the pedal harder, the valve 'pops' open suddenly, giving the car an unintentional burst of speed. All of this happens if the sensor is unable to detect the closed position of the throttle.

 

[Biologist]

Thanks for the replies so far. I have no check engine light on and no codes. The spark plug type I can't remember, probably Autolite Platinums, I will have to check when I get home. The wires are just ebay spark plug wires but they seem to work when I test with inline spark tester. I will read more about replacing the MAF or TPS. Tired of throwing money into this thing!

http://www.toyota-4runner.org/3rd-gen-t4rs/111387-throttle-position-sensor-fix.html

This does sound very similar to my problem. Gonna measure my TPS tonight with my ohmmeter.

 

[Biologist]

I got time to work on it this weekend and used clips and hooked up my ohmmeter to the two outside pins on the throttle position sensor. Then I slowly moved the throttle by hand. At the starting bottom range there is a dip of non-linearity in the resistance. It starts at say 0.54 (sorry can't remember the multiplier on meter, maybe 540 ohms?) or so and increases to 0.62 but then goes back down to 0.58 or so and then back up. It is subtle but reproducible every time. I'm hoping that the partial throttle problems are due to this inaccuracy. I bought a new TPS on ebay for $22 and will report back here if it fixes it. Thanks for all of the advice.

 

[snivilous]

I had a similar problem start as I was driving from CO to UT last week, pretty sure it's my torque converter going out since there's a grinding ish sound when in drive but not in neutral and everything is still shifting fine. Food for thought.