kyle1

Hello. First post, but long-time lurker.

I've been having throttle response issues for about six months. While cruising, sometimes the car will just lose power and kick down to about 1500 RPM. When this happens I have no throttle response unless I let off the gas for a few seconds and then try again.

At first it only happened when in cruise control after the transmission downshifted to go up a hill or something. It was like it would forget what gear it was supposed to be in and just lose throttle power as stated above.

Recently It has been happening more often even at slow speeds and from standing still.

I tried searching, but couldn't find anything. Anyone ever had this problem. Sorry if I didn't explain it well.

I drive a 2002 4WD 3.4. It is lifted with 33/1050s, but still have factory 3.90 gears. This may or may not be important.

Any advice is appreciated. I would like to avoid the dealership.
Thanks.

scuba

4Runner or Tacoma? Sounds like its an auto.
Have you had the transmission fluid changed or flushed?

kyle1

Sorry. It is a 4runner auto. I drained and refilled the transmission right after it started, but did not clean the screen or change the filter. The fluid looked fine and wasn't dirty, but felt a little thin.

kyle1

Any ideas? I'll be changing the spark plugs and wires and doing an oil change this weekend. Anything else I can check to try and troubleshoot? Should I check any sensors? Could the fuel filter be causing the problem? Also, could reseting the computer help?
Thanks for any help!

sam333

Do you have any codes showing? What year and how many miles?
I would do a tune up first( using the manual) and check your MAF and TPS .

Texas_Ace

I have an issue just like this every now and then, very inconsistant and annoying. Happens maybe 3 or 4 times a year for a day then goes away.

I have found that it simply cuts either fuel or spart, or both at ~1800rpm's, above or below that it runs perfect. Since the problem never sticks around i am never able to work on it to figure out what it is.

Whenever it happens i just keep the rpm's above 2k and i am fine and it usually goes away next time i go someplace or the next day for sure.

kyle1

That sounds like the same problem. It makes me feel a little better that someone else has experienced it.
It is a 2002 with around 150,000 miles. No codes. It just acts as if it is hunting for the right gear sometimes. Very weird, and of course, it usually happens at inopportune times (like the terrible drive from Denver to Salina, KS).

kyle1

I am still having this problem. After the original post, I changed the spark plugs and wires, fuel filter, cleaned the MAF and throttle body, and ran some injector cleaner through it. All the new parts were factory Toyota. I thought it was better at first, but now it seems to be worse.

The more that I think about it, it seems to be either a fuel delivery problem or a vacuum problem because I have to let the rpms drop to idle before revving back up to fix the problem. It still loses power between 1500 and 2000 rpm, but it seems to be worse when windy, going uphill, or when I throttle down to go around a bend.

I am not really familiar with how to troubleshoot the fuel delivery or vacuum systems. Any help would be greatly appreciated.

Thanks so much!

-Kyle

BajaRunner

Sounds like a TPS to me?

Texas_Ace

Yep, same problems i have had, never did figure out what the problem was, it comes and goes about twice a year.

kyle1

Wouldn't a failing TPS throw a code? If not, how can I check the it? If it is bad, I assume I'll have to buy a new one...and I assume it's expensive?

Thanks for the quick response!

Texas_Ace

I tried a new TPS on mine, seemed to help at first but it came back a few months later.

I just gave up trying to figure it out, it is something electrical i am almost positive no clue what though.

Mine would just cut out at exactly 1700-1800rpm, above or below that it was fine.

BajaRunner

http://ncttora.com/fsm/2003/Repair_M...rbodwe/ovi.pdf
See page #2, Step 3)

There is only one resistance check on the TPS, which seems like a little vauge to me.

A failing TPS wont always throw a code either.

4rx

Did you take the idle air valve control off the throttle body and clean it? If not, clean it.

It did make a difference once I cleaned IACV but mine is manual transmission tho...

Beto

Hey guys, I might be wrong here because I tend to really, really hate VSC when it doesn't work right, but this sounds very close to what the VSC does.

In the 2002 4Runner you have a partial "drive by wire" system for throttle. If you look inside the throttle body with the key off and push the pedal to the floor it only opens the butterfly about 10% or 15% of the way. There is an electric motor or clutch or something that opens it the rest of the way. The VSC system can dethrottle the engine to stop a slide. This works when actually sliding, but also tends to trigger when you aren't - like turning left from a dead stop in front of oncoming traffic - it gives you just enough throttle to present a broadside target then leaves you stuck there pumping the gas pedal until it kicks back in.

You might want to investigate this option before spending time diagnosing your engine(s) more. If anyone can make this happen reliably (not intermittently), then pull the pressure sensor wire off of the master cylinder to disable ABS, VSC and TRAC systems and then try to make it happen again. If it goes away, it's 100% that your VSC is causing this.

Do a search for the ANDY MOD, VSC, BAGEL MOD if you are interested.

kyle1

Thanks everyone. I will check the TPS and the IACV. I had not thought about attributing the problem to VSC. It feels a little different from when I spin the tires on a gravel road or something and the VSC kicks in. I might still try disabling VSC for my next road trip though. It seems worse when driving long distances.

Thanks again.

javadoody

i was going to guess the fuel filter, but now that's new. still think fuel, either the pump or a leak in the system. am i correct that the gas is always in vacuum? open the gas cap and you should hear vacuum released. try pulling over when you lose power and see if that's the case.
correct me if i'm wrong here guys, i'm real new to the 3.4.

Texas_Ace

If itwas the same problem i was having i highly doubt it is a fuel problem. Fuel problems don't just suddenly hit like a ton of bricks and then disappear just as fast. They usually come on and go easy if it is a pressure issue. If it is a failure issue then they don't come back on.

In my case i am 98% sure it is an electrical problem.

Texas_Ace

Figured i would bump this back up as i learned some stuff about it today.

So i had this problem happen to me again yesterday. Would lose all power right around 1700rpm.

Well this time i had my wideband hooked up and noticed that i was running really lean, like 17:1 lean. And it was actually lean all over the place except idle or WOT. but around 1700rpm's it would go full lean and lose power.

So with this in mind i am thinking it might be something to do with the MAF or O2 sensor even though i don't get any codes. It is fixed again today so i am not worring with it but figured i would let ya'll know.