NOBODY has been able to figure this out.. PLEASE HELP

I have a 2005 Toyota Tacoma PreRunner 4.0 V6, which has been the most reliable vehicle I’ve ever owned.. until recently..


It seems like everything started about a year or so ago. I was in my truck with it running in park, and I looked down and noticed my truck was pegged. There’s no telling how long it was running hot. I immediately turned it off, let it cool and topped off the antifreeze.


About two to three weeks later, it started skipping badly when going up hills. I cleaned the MAF Sensor and replaced all 6 of the Coil Packs, thinking this would help. It did okay for a while, but then I noticed I was needing to fill the coolant up every few days. I thought the head gasket was blown, and noticed water coming out of the tail pipe. I used Blue Devil, which seemed to fix it because it’s not leaking anymore and there’s no oil mixing with the coolant.


Replacing the coil packs seemed to fix the skipping and sputtering problem when accelerating up hills, somewhat.


Eventually, however, my truck has started to have an extremely rough idle. When cranking up the truck, it spits and sputters so badly it’ll stall out if I don’t rev up the engine right away. When I take off and drive a couple yards, it drives okay until it stops and idles. Then the process starts again. This happens more frequently and does it way worse when the weather is hot. When it’s cold outside, it may do it if driven for a while but no where near as badly.


Throughout this whole process, the check engine light has only gone off about two weeks when the coil packs were replaced, so it’s basically been on constantly.


I’ve replaced the crank shaft sensor and one of the cam shaft sensors (the driver’s side - which was the one throwing the code.) I’ve also replaced both upstream Air Fuel Ratio o2 Oxygen Sensors and the PCV Valve.


The truck is still throwing p0171 and p0174 and P0300 (see attached file for Live Data Sheet and attached images for up to date diagnostics scan)


I have no idea what could be the issue. I’ve taken it to several friends who work in the automotive industry, and have searched online hours upon hours to no avail. If you have any knowledge or advice about what this issue could be, I would VERY MUCH appreciate it!

Thank you in advance!!

 

Have the coolant checked for combustion gasses. If you were losing coolant, it was going somewhere.

 

It more sounds like a warped head. You'll need to do a leak down test, or watch the cylinders while they are pressurized and use a borescope.

The lean condition could be head related, or possibly a vacuum leak or a weak fuel pump. It's hard to say.

 

The 05-06 V6 Taco head gaskets appear to have higher than average failure rates among the second gens. Many of the symptoms you describe fit a bad head gasket. Do a compression test and test the coolant for exhaust gases.

 

+1 on that. Also do a cylinder leak down test and take a look at the fuel pressure. Failing fuel pump can cause those lean codes.

 

Easy way to check for exhaust gases is make sure your coolant is full. Take the radiator cap off. Start the truck. Look into the radiator and watch for small bubbles to come up where the cap should be. If you see the bubbles you have a head gasket issue. My 2005 had a Very Small Hole in the head gasket. It never over heated or threw any codes. All I noticed was I had good heat while I was driving down the road. When I would stop at a red light the fan would blow cold air. Once I would leave the red light I would have heat again.

 

I had these symptoms on my last truck. It was a head gasket.

 

I agree with everyone above about a problem in the head and/or head gasket.

Two suggestions:
1. Look on the underside of the oil filler cap. If you see something that looks like dirty milkshake, there's been coolant in the oil. Clean the cap, change the oil, and be on the lookout for new milkshake. If it appears, you still have coolant leaking into the oil.
2. While the engine is cool, remove the radiator cap. Now start the engine and try covering and uncovering the radiator fill neck as the truck warms up to see if you can change the idle by doing it. If so, you have a coolant to intake, cylinder, or exhaust leak. I did that once to get a free head replacement including labor from a mechanic who had just replaced the head on my last Toyota truck. Obviously, don't burn yourself as the truck warms up. This test doesn't always work, but if you can alter the idle, you definitely have a problem.

 

The kit to check for combustion gases in the coolant system is really easy to use. The

$64 UView 560000 Automotive Combustion Leak Test Kit for Head Gaskets, Cylinder Heads and Engine Block Leaks, Gas/Diesel Engines, Dual-Chamber Tester Filters Alkaline Particles, 16oz Testing Fluid

UView 560000 kit is on Amazon is a little over $60. I believe Harbor Freight aslo sells a kit for less than $30 (don't know how they compare).

There are many vids on YT that show their use.

 

Sounds like a head gasket for sure...I bought a combustion test kit for about 30 at NAPA...Easy and accurate.

 

You can also rent one at autozone for 30 and get your money back when you return it , you just have to buy the fluid for 10

 

Unfortunately, it sounds like a head or head gasket issue. Compression test & coolant analysis like the previous posts have suggested.

 

Wondering if the original problem was a stuck thermostat which caused the overheating and possible now warped head / head gasket issues.
Interesting for sure....keep us posted

 

I agree with the others above. You may have had a small issue with the head gasket and the coolant was low and caused the overheating. Overheating is bad for older engines with cast heads and blocks. With aluminum it is devastating.

Armchair evaluation: At best you have a blown head gasket, at worst you have a warped/cracked cylinder head or block.