Need help!

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lefty556

New member
All,

I've got a weird issue on my 2000 T4R. I'm getting a weird surge out of the engine. I'll be holding the accelerator steady, but you can feel and hear the engine revving up and idling back down. It doesn't show up on the tach, but it can be heard and felt. It's almost like it's not getting enough gas or enough air. It's happening on a daily basis, and been happening for about two weeks.

Different brands of fuel. Everything has been mid grade or premium. I swapped out the air and fuel filters about 2500 miles ago. I did the ISR mod at the same time I replaced the plugs and wires, about 1100 miles ago. No change in fuel economy or performance, but it's weird and annoying.

I did get a P0420 code last weekend. I cleared it out, filled up with premium, and haven't seen it since (180 or so miles).

Any ideas on what to look at to try and figure out what's going on?

Thanks!
 
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I agree, it sounds like it could be an accessory cycling. Battery voltage is good? Alternator isn't acting up? A/C and defroster is off?

If it was the engine, you'd see the tach move. You could also try turning overdrive off (button on the shifter) and then see if the tach moves at all or cycles. It's hard to tell with OD on at highway speeds if it really is the engine since the torque converter sometimes doesn't allow the RPM's to move much.
 
It's not the A/C. I haven't been running the A/C yet this year.

As far as I can tell, the alternator is good, but I haven't been eyeballing the voltmeter on the dash.

I'll try kicking the OD off and see what happens.
 
lefty556 said:
It's not the A/C. I haven't been running the A/C yet this year.

As far as I can tell, the alternator is good, but I haven't been eyeballing the voltmeter on the dash.

I'll try kicking the OD off and see what happens.
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I don't know the climate where you are at, but if you have the front defroster on the A/C will turn on without the light turning on. I didn't believe someone when they mentioned it a few weeks ago until I tried it and sure it enough it does! I rarely ever use my front defroster though.

Also, if it's at all possible to get a sound or video clip (safely) that you could upload that would help immensely.
 
gamefreakgc said:
I don't know the climate where you are at, but if you have the front defroster on the A/C will turn on without the light turning on. I didn't believe someone when they mentioned it a few weeks ago until I tried it and sure it enough it does! I rarely ever use my front defroster though.

Also, if it's at all possible to get a sound or video clip (safely) that you could upload that would help immensely.
Click to expand...

It makes sense given that the AC is used to remove the moisture in the air.
 
I'd get some better diagnostics with an OBD scanner. It'll tell you how much the RPMs are jumping around, and you can also monitor exciting things like LTFT and STFT, O2 sensor data, etc, to see what might be changing with the RPM surges.
 
I was having a similar symptom with my 02 Taco.

At highway speed around 62-65 mph, throttle held at a certain spot to keep speed on the highway, the engine would hiccup/skip for just a second. Could feel it but to small for the tachometer to pick it up.

Found out it was the Throttle Position Sensor had a dead spot and every time I hit that certain spot it make the engine "hiccup"

I think the previous owner did a lot of highway miles since I bought it with 215K on it and it would only happen at a certain position of the TP sensor while keeping the truck at a certain speed.
 
I suspect TPS as well. When TPS goes bad, you can notice the RPM jumping up and down. I noticed a faulty TPS on idle and the RPM went up and down on my 5 speed toyota. Stay with an OEM TPS.
 
The CEL hasn't come on, but there is a pending P0420 code in there. My scanner shows a constant 0 volts for the Bank 1, Sensor 1 O2 sensor. Bank 1 Sensor 2 shows anything from .1 to .7 volt.

I can't see the RPM bouncing on my scanner, but it's a WiFi scanner and has a little lag, plus it's kinda hard to watch that and drive.

The RPM surging/bouncing doesn't happen sitting still and idling. I only encounter it while moving. Typically when the engine is between 1800 and 2200 RPM.
 
cfranck1 said:
I was having a similar symptom with my 02 Taco.

At highway speed around 62-65 mph, throttle held at a certain spot to keep speed on the highway, the engine would hiccup/skip for just a second. Could feel it but to small for the tachometer to pick it up.

Found out it was the Throttle Position Sensor had a dead spot and every time I hit that certain spot it make the engine "hiccup"

I think the previous owner did a lot of highway miles since I bought it with 215K on it and it would only happen at a certain position of the TP sensor while keeping the truck at a certain speed.
Click to expand...

I totally agree with this. I had same symptoms, no codes, my 4runner ran great, except at a certain speed, about hiway speed. On the other hand my x-wifes volvo did the same thing and finally determined it was the TPS. ( the volov one was about 300) So I thought , what the heck,its not a ton of money ( under 50 if I remember correct) and had gone through everything, cleaning maf, cleaning throttle body , full tune up, fuel filter adjusting slack out of the cables so thought, why not try it

problem solved
 
So, I'm still having the issue. It occurs between 1900 and 2100 RPM, regardless of speed. I haven't had any form of A/C or heat going, as the weather has been nice.

I replaced the TPS last night. Did a double check on both the battery and alternator. They're both A-Okay.

No CEL. No pending codes.

Any other possibilities?
 
I don't have access to a Toyota Handheld Tester.

I went ahead and replaced the fuel pump. Based off of everything I know on this thing, it was bound to be original, so replacing can't hurt. I used a Denso 950-0100 pump/strainer kit and a Denso seal.

No joy. Still getting the surge. Still not pulling any codes.

I did notice that I have an exhaust leak. There's a partial failure of the gasket where the Y-pipe goes into the front cat. Could that be causing my problem?
 
I've got a bit more info to add. I had a co-worker go to lunch with me today, so I had someone that could keep an eye on the OBD Fusion app on my iPhone while I was driving.

The surging issue occurs in all gears when I can hold it between 1900 and 2200 RPM. It's worse in 2nd and 3rd than it is anywhere else, but it occurs in every gear.

In park or neutral, I can easily rev the engine to the redline. In gear, not so much. If I stand on the accelerator, it'll get to 3000 RPM, but barely, and not quickly.

When the surging occurs, the Bank 1, sensor 2 O2 sensor voltage drops down to the .1-.2 volt range. When I gas it to get out of the surge, the O2 sensor reads between .6 and .8 volts, depending on how much I'm on the throttle.

The exhaust leak is apparently getting worse, as it is louder today than it was over the weekend.

No codes showing as set or pending at this time.

Anybody have any idea on what I should look into?
 
So I replaced both cats, the A/F sensor and the O2 sensor last night. Holy crap! the difference is astounding!

The surging is, so far, gone. The 4Runner will accelerate going uphill now. I can easily hit 70-80 on the highway now. Looks like the problem is solved!
 
lefty556 said:
So I replaced both cats, the A/F sensor and the O2 sensor last night. Holy crap! the difference is astounding!

The surging is, so far, gone. The 4Runner will accelerate going uphill now. I can easily hit 70-80 on the highway now. Looks like the problem is solved!
Click to expand...

That's great. Kind of an expensive part chuck but as long as it's fixed it's all good. Assume you used AM cats. Which ones did you use? Walker? Bosal?
And hopefully you used Denso sensors.
 
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