05 regular cab troubles

Alright I bought this truck (05 regular cab 4x4 2.7l manual ) on January 13th that just so happened to be a Friday.
I now have a CEL had it checked I don't remember # but something like coolant temperature below factory spec. The temp gauge on the instrument cluster doesn't work. Replaced thermostat didn't help. Has a very odd idle. When removed from any gear to come to a stop it jumps to around 2500 rpm down to 2000 rpm. Now it seems to have a horrible miss when driving between 1500 rpm to 2000 rpm but not noticeable at highway speeds. No CEL for the miss that I know of. Where do I start with this thing?

 

Coolant temp sensor

 

Where is it located? Isn't there 2?

 

It's on the drivers side, kinda behind the manifold towards the back. You can check if it is working by measuring the resistance across the pins at different temps. At 68F it should be 2.3-2.6 kohms, at 175F it should be .3-.33 kohms. If it checks good, then you need to look for an open in the circuit.

 

The code is P0128

 

That's coolant temp yes..

 

The 2004 FSM Diagnostics section lists 4 trouble areas for a PO128 code:

- Thermostat
- Cooling system
- Engine cooling temperature sensor
- ECM

 

Sounds like what others have mentioned. Faulty coolant temp sensor. On the 05 I'd recommend checking if the original water bypass pipe is still there. If so replace the plastic one with the correct metal version. You will have to drain the coolant as it is and trust me you don't want to pull the intake manifold off twice.
Components I'd recommend replacing while in there.

- Knock sensor
- #2 Coolant water bypass pipe
- #2 Coolant water bypass pipe gasket
- Coolant Temperature sensor (rear engine block drivers side on cylinder 4)
- Intake manifold gasket ( Felpro gasket is want I used and was identical to the OE)
- Throttle body gasket (Felpro gasket was incorrect size. I used a Toyota gasket)

 

Ok got the truck back from stealership. Engine coolant temperature sensor fixed but still seems to have a hesitation on acceleration. Has 4 new Denzo iridium plugs. & no CEL

 

Does it have a k&n air filter?

 

I see where you are going good but a hard start issue won't be from the MAF. Mine had an over oiled K&N for years no problems. The only issue I had with it was the oils coated the IAT resistor and it was 35 degrees off all the time. Even still it started fine. If you disconnect the MAF on a second gen the engine dies.

 

Hesitation finely turn to a full blown miss. Missfire #1 cylinder. Coil replaced

 

How's the hot start?

 

Every time today it didn't skip a beat fired right up

 

Keep an eye on everything for some time. Hopefully your fixed.

 

I hope

 

After the repair it might have taken the computer time to re-adjust so the engine would run right. Usually, when I switch from 91 octane to 87 octane I disconnect the battery for an hour or so to let the computer adjust to the new octane. Recently I found 87 octane ethanol free where I live. I never disconnected the battery but after a couple of tanks the computer re-adjusted itself and this truck now runs as good as it did with 91 octane with the deathanol in it. I'll be running 91 octane deathanol free in the summer and 87 octane deathanol free in the winter from here on out. I have access to both but at different stations. Engines run so much better on deathanol free. Ethanol needs to be outlawed. It does nothing but negative things for the environment and ruins fuel mileage. My 2.7 loves the deathanol free. It seems to like the 87 octane even more than the 91 octane. I'll run the 91 again this summer and see if there is a difference. I may just end up running the 87 year around although I've been running 91 just about all the time since I bought it a couple of years ago. The 91 with the deathanol seemed to just make it run better but I could never put my finger on it. With 87 octane deathanol free I have noticed a big difference.