Engine loses power intermittently.

Tiny
AYKOSS
  • MEMBER
  • 1994 TOYOTA 4RUNNER
  • 31,147 MILES
Hi, I have a 1994 toyota 4runner v6 sr5. I have a problem with the engine losing power intermittently. The motor loses power and and if I put the clutch in and rev it runs perfect again. It started doing it only on one particular slight hill on my way to work. (Steeper hills were fine). Then it gradually got more frequent. Changed fuel filter. Still did it. Changed spark plugs, and it ran perfect for 1000km or so, then it started again but way more frequent. It doesn't seem to do it too much above 3000rpm. I have taken it to three different mechanics they had no idea. "Drives beautifully" they say. Any help would be greatly appreciated. Cheers!
Sunday, July 1st, 2012 AT 4:31 AM

19 Replies

Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
Can you tell if it feels like a miss fire (electrical ) or a gradual power loss more like fuel starvation, have you check the fuel pressure as yet?
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Sunday, July 1st, 2012 AT 5:12 AM
Tiny
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Gradual power loss until I pump gas, then runs perfect again. Sometimes when idling rpm will drop from 1000 to just above zero eventually stalling after around a minute. Haven't checked the fuel pressure, will read up on how to. Thanks!
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Sunday, July 1st, 2012 AT 5:58 AM
Tiny
MHPAUTOS
  • MECHANIC
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Let me know what you find with the fuel pressure.
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Sunday, July 1st, 2012 AT 7:17 AM
Tiny
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Will do. Wanted to ask, is there any reason it ran perfectly for a while after the spark plug change? Coincidence? Also could it be the o2 sensor? As I was running it on e10 fuel for a while and apparently that can make them fail.
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Monday, July 2nd, 2012 AT 12:12 AM
Tiny
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  • MECHANIC
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If the O2 sensor fails you will normally get a code up for over rich on one or both banks, manually testing o2 sensors are not very easy, they do wear out and as they do they tend to cause a rich mixture, an exhaust gas analysis will b e the best way to test for this.
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Monday, July 2nd, 2012 AT 12:36 AM
Tiny
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I can't afford to have it in the mechanics at the moment. Do you think it's worth me cleaning the maf sensor? I have no check engine light showing though. Thanks.
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Friday, July 6th, 2012 AT 7:53 AM
Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
Can't hurt, give it a go and see if it helps any.
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Friday, July 6th, 2012 AT 8:51 AM
Tiny
AYKOSS
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  • 16 POSTS
Hi, having trouble locating the maf. Took the air box off and assumed the maf is the thing bolted to the top, it has a little door flap thing inside and behind that a little plastic tube sticking down. Is that the thing I have to spray? Cant find any info or pics on the net, do you have a diagram of it? It's not even in the manual. Thanks again for you help!
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Saturday, July 7th, 2012 AT 4:21 AM
Tiny
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Ps. The air filter was absolutely filthy dead flys and small rocks and sticks in it!
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Saturday, July 7th, 2012 AT 4:23 AM
Tiny
AYKOSS
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So I cleaned the rocks and dead fly's out of the air filter (will buy a new one tomo) and the truck runs a hell of alot better. Still cant find the MAF (the thing I was looking at I think is the AFM) would still like some info on MAF if possible so I can clean it when I change the filter. Thanks.
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Saturday, July 7th, 2012 AT 6:14 AM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
The MAF is the flap thing located in the air path between the filter and intake/throttle body. No need to completely remove it. Just remove the air hose it's mounted in and spray it with carb cleaner. Don't touch it. Your finger oils and acids can ruin it.
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Friday, July 20th, 2012 AT 3:56 PM
Tiny
AYKOSS
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  • 16 POSTS
Hello again. After no success diagnosing my problem I decided to take it to the mechanic, they serviced my throttle body and reset the base idle cause it was all set wrong and my timing was out too. Now after $300 my truck runs worse! Now it bogs down badly sometimes from take off, very sluggish, slight misses and pops from the engine. And then drives fine again. Also bogs down when just cruising. If I floor it, it drives perfectly. So I guess what i'm asking is, why would of the previous owner screwed with the throttle body and advanced the timing? And it run worse when it's now set correctly? Any idea's would be great. It's been to 4 mechanics now and is worse off. Thanks.
Ps. The fuel pressure still has not been checked. I did ask for mechanic to check but said the pump either works or not.
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Sunday, August 5th, 2012 AT 1:38 AM
Tiny
AYKOSS
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These are the things i've replaced.
New plugs and leads, ran perfect for 1200km's. Then prob started again.
New fuel filter.
New rotor button.
New air filter.
Replaced air flow meter.
Reset base idle and throttle body service.
Timing has been corrected.
Engine light not on, scan machine detected no codes.
Read alot of forums with same prob, same model, but no solution. What could it be?
Thanks.
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Sunday, August 5th, 2012 AT 5:24 AM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
Your mechanic is wrong. A pump CAN lose pressure but still provide fuel. Just not enough.

The internal timing could have either slipped or been set incorrectly after a service procedure. Pull #! Spark plug and rotate the crankshaft clockwise to bring the #1 piston to top dead center on the compression cycle. Then remove the distributor cap and note which spark plug the rotor is pointing at. And then check the timing mark on the crankshaft dampener.
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Sunday, August 5th, 2012 AT 1:43 PM
Tiny
AYKOSS
  • MEMBER
  • 16 POSTS
The 4runner is running worse than ever! I still never diagnosed the problem, it ran fine with the occasional bog down from late winter, until early summer and today (being the hottest day this summer) was running very badly displaying symptoms described above. So, temperature must be a factor in diagnosing this problem, as it runs perfectly displaying rare hiccups in spring and autumn (mild consistent temps) and very bad in summer/ winter ( erratic extreme temps)

also im starting to hear clicks when the motor bogs down on the right hand side of motor.

Any ideas would be great, thanks.
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Tuesday, January 8th, 2013 AT 3:41 AM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
Check the temperature sensor and make sure the coolant is flowing when it gets warm.
Also check the fuel pressure when the engine gets hot and starts bogging down.
Also check the timing.
When was the last time you ran some good injector cleaner through it?
So, where in the Southern Hemisphere do you live?
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Tuesday, January 8th, 2013 AT 4:58 AM
Tiny
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Ok thanks i'll try some injector cleaner, haven't put any in for about 6 months.
I live south of sydney on the coast, average temp would be about 22'c.

I took it to the mechanic today, he drove it and said it might be the coil pack.
Does that sound like it could be it?
This will be the 6th time I have had the truck in for this undiagnosed problem, it's sending me broke!
Thanks alot for your help.
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Wednesday, January 9th, 2013 AT 5:59 AM
Tiny
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I think I may have solved this problem!
I unplugged the TPS and she runs like a dream!
Thanks for all your help.
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Wednesday, January 9th, 2013 AT 7:13 AM
Tiny
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My pleasure. I live a bit north of you. I'm in Brazil.
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Wednesday, January 9th, 2013 AT 4:08 PM

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