I am still trying to figure out what is going on with my truck. I have a 1999 tacoma ext cab, 4x4, 2.7L, 5 speed, 240,xxx miles.

About 2 months ago I did a tune up that included oil+filter, air filter, new plugs+wires, cleaned MAF and Throttle body.

Just last week the truck started to hesitate and cut out under load. Since then I have replaced the fuel filter, fuel pump, TPS, and swapped out the MAF with a working one from a friends truck and found that wasn't the problem. With the help of my dad just yesterday he told me it has to be loosing spark or out of time because he said he can smell unburnt fuel coming out of the exhaust pipe. I had the truck in neutral in the driveway, I can rev almost to 5K then if I hold the pedal there it cuts off and bogs down to around 1 K, then sputters and tries to run but is very rough. Sometimes it will backfire through the intake and pop. When I let off the gas pedal it will idle nice and smooth around 750 rpm.

I was told it could be the timing chain jumped a tooth? Or the guides had broken inside the cover? The problem I have with that is I don't hear any noise from the engine. I had a 22r that had broken guides and it doesn't sound anything like that did.

I was also told the crank sensor could be bad, or the knock sensor could be bad. These were all guesses from people that assured me the fuel pump, and TPS needed replaced so I will hold off on those.

One of my dads friends who said he worked at a Toyota dealer, over ten years ago, told me to check the coolant temperature sensor. I did have a bad one on my old 1994 4 Runner, but it didn't have this kind of affect on the truck so I am not sure about that either.

Any help would be great. Also, the truck has yet to have any codes so I really have no direction to go in.

 

It can't be a misfire or the engine would have thrown a code within seconds. My guess would be something along the lines of the timing or the distributor cap having condensation in it.

 

99 Tacomas do not use a distributor, they run coil packs so that can't be the problem.

The timing guides didn't likely break nor did the chain "jump a tooth" either. It would be notice from idle all the way up the spectrum.

If it was knock sensor you would have a code. TPS is certainly a possibility, one that is much more likely than all the others so far. I had a similar problem with my 86 4Runner after rebuilding the engine. Turned out to be a strange coincidence, but the TPS had gone out and was causing the engine to run very very rich.

 

It has a new TPS on it.

 

knock sensor and crank shaft sensor checked out o.k. I will check the knock sensor wiring harness next.

My question about this is I started the truck without the knock sensor and the CEL came on very quickly. The truck ran exactly the same with the knock sensor removed and unplugged. Does this mean that the wiring and the sensor are o.k. and not the problem?

Could this be a coil pack issue?

Very stumped right now, need this truck for work so any response or idea's would help right now. Thanks in advance.

 

You know what I do when I can't figure something out - take it to the stealer and quit the bleeding. At least here you pay $95 for diagnosis even if it takes them 2 days. I had my truck there for a CEL and it was there 1.5 days and they couldn't reproduce the problem. They didn't charge me.

Always with electronics, it is possible (but rare) you can just get a bad one right out of the box (I am talking about the TPS).
Did you try checking your injectors? Run some BG 44K through it and see what happens. It is about $25 / can but it is awesome stuff and WAAAYYY better than seafoam.

 

I messed with the truck last night and found out that it is a timing issue. I tested each plug wire and they were all o.k. I also checked for spark with this in line thing my dad has, you plug it between your plug wire end and your spark plug and it lights up, they were all o.k. Then I put the timing light on the truck and found that when the engine revs up it advances like I expected it to. But when it starts to stumble and sputter, the timing mark goes the opposite direction past zero. I assume this is a timing issue, I just have to find out what controls the timing. I know the crank sensor and knock sensor have something to do with it. Does this engine also have a cam sensor? Anyway, I believe I am headed in the right direction, if not please let me know.

 

I replaced the crank position sensor and my problem has slowly went away. When I put the new part in, it ran alot better in neutral, but on the test drive it still stalled just not as bad. I needed the truck so I drove it anyway and it has been getting better by the hour. After a couple of trips the stalling problen is all but gone. It still has a little blip around 2K but if I press the pedal down further it keeps on truckin, not like before.