it was not the pick up coil. the limp mode would pull a code right? tomarrow we will try a new air flow meter, we'll see. thanks for the sug

 

well we replaced the air flow meter and it still did that damn problem again. here is a link to a short video of the tach when it acts up (not the best quality but it gets the point across, i hope). i have a few other ideas left so i will update when i get them done.
http://s63.photobucket.com/albums/h1...t=100_0788.flv

 

it sounds like something my 82 hilux used to do when the fuel filter was clogged.

 

I have the same truck but I've never experienced what your talking about...

Is the A/C on during this? Could it be linked to the AC throttle up?

 

the a/c is not opperational and we changed the fuel filter twice (this is what i first thought it was, it happened to my 80).

 

You figure this out yet?

 

I will pose two possible suggestions. 1) your cat is clogged up, when it gets hot enough, after driving for 20-30 mins like you say, the walls of the internal passages expanded and choke out the exhaust. This allows no throttle driving to still occur uneffected because of the lower exhaust volume. or. 2) in the fueling system, either the fuel filter is clogged and can no longer keep up with the demand of the motor or the pump is going and again can't keep up with the demand of the motor at speed. Either way if it is a clogged filter or weak pump they should be able to handle idle but not higher revs.

 

have not figured it out yet. now that you mention it did blow a new cat gasket infront of the cat. as you can see in the short video it reves like that but idles fine. but it goes away in a min or two, then runs fine. thanks for the ideas i will try the cat maybe sunday. the FF is new and it showed the problem still the day of the new filter install. do you know if there is a filter screen in the tank before the pump?? i will give an update sun night or monday. keep the ideas comming i am grateful for all of the suggestions.

 

well i was able to work on it for a little bit sat night. i pulled the cat looked in the inlet side and i could still see through it (a couple of passages were plugged). then i turned it around and looked in the outlet and this is what i saw.
so i put a test pipe on and drove it for a little drive for about 1 hr and it did not act up. then today i was driving the truck back to him and i had it on cruise going about 65 and prior to this it had plenty of power and ran great, the cruise stopped like when you tap the brakes or push in the clutch. power stopped and did like it did in the video. ~30 seconds later all power is back like it never acted up.
i am starting to think it is a electronic sensor. like the tps (? sending a signal to the ecu that the throt is only open a little??). he has had the entire motor/front 1/2 of the truck under water. did a compression test and they were all about the same, only 5 psi difference in #1.
i still think that that for some reason the ecu is cutting the spark and fuel injectors off????

 

i am guessing this is an automatic ?

 

it is a 94 4x4 5 speed with the 3.0 v6.

 

and at nowhere during this time does he push in the clutch?
it the engine revs and drops in RPM's with the clutch out you have a very bad problem ..lol

 

when it happens if he pushes in the the clutch and does not touch the thrott the motor idles like normal.if he pushes in the clutch and pushes down the thrott it acts like in the video. if the clutch is not pushed in and the thrott is depressed it will bounce the truck like he is opening and closing the thrott to make the truck bounce up and down (like when someone is trying to be a jerk, or when slowing down tjo a stop and keeps hitting the brakes and making the truck bounce as it slows down to stop).
and yea it is a bad problem, his truck has been pushed to the limits and beyond what it should have (back when he was in high school) so this truck might be retired soon.

 

check the fuel pump .

 

ok i will do that soon.

 

as was mention before it may be an o2 sensor. my gf has a honda accord (automatic) and this was happening to her. the rpms would drop and shed have like no power at all. turned out to be an o2 sensor.

 

i pulled it and looked but didnt test. i will try a new one and see what happens. thx

 

My dad has the problem on his early 90s pickup, he cleaned the throttle body went right away.

 

Bad TPS,,, throttle pos. sensor....... Replace

 

fwiw, not sure if this is fixed yet or not, but that's EXACTLY what happened to mine when the clutch went bad. i can't recall which parts of it were hosed, but that is precisely the symptom.... you'll be going along just fine and then zzzzzzzrrrrrr, no power, just like you put the foot down on the clutch, then a couple seconds later, you're back in business.