Is your IAC functioning 100% or are you just assuming that a response in idle to engine temp means this part is OK. This part played havoc with my 5VZ-FE.
Well, I bought a a new sensor, switched it out, and it did not help. I think it is something in the circuit other than the sensor, although I think the sensor is playing a part too. My temporary solution is to leave the sensor unplugged. Not sure if this is doing any harm…
My 1988 Pickup is doing the same thing. Will try the corrective actions listed above.
As mentioned elsewhere, it’s possible there is a problem in the circuit which connects the ECM, intake air sensor and coolant sensor, and possibly the cold start injector. My thinking is that for some reason, the system thinks the engine is ALWAYS cold, therefore always activating the cold start injector and flooding the intake (just thought of a way to test this). For me, when engine is hot (and temp sensor connected), I crank the engine while pumping the gas for about 5 seconds (don’t want to do it any longer), then turn the ignition off. Then, I do the same thing again and usually it starts up after another 5 seconds. Of course letting the truck sit for about an hour allows it to start right away.
I have mostly been driving with the intake air temp sensor unplugged with no adverse effects yet. I have still been getting about 27-28 mpg average, which is what I was getting before I drove with it plugged in.
You guys do realize that when you unplug the air temp sensor you’re just putting the ECU into “Limp home mode” which means it goes into its most basic form of running/starting and doesn’t listen to any sensors. Its just uses the base map built into the ECU.
This “limp home mode” will allow the car to start no matter what, if all of the mechanical engine things are in check. This is why it does not mean its the air temp sensor causing the problem, and I can absolutely guarantee that replacing the air temp sensor is not going to fix it. Its the first thing a million people have done. And it doesn’t work. Plus if you want to see if it changes anything when the air temp sensor is cold, just take it out of its holder and spray some cold air on it. The truck still will not start.
I think the real issue is the coolant temperature sensor. Its getting heat soaked from hot coolant leaking towards it after the engine shuts off. This is a common thing that happens on every vehicle(except the hard start). I have not fixed my hot start issue yet, but I am thinking of moving my coolant temp sensor to a different location(right now its right beside the exhaust manifold). I’m thinking of moving it to the other side of the engine and seeing if this fixes the problem.
I’m going to get another sensor relocate it, leave the other one in place, and when the truck won’t start I’m going to plug the other one in and plug it into the other side one and see if it starts. I truly believe this is the reason for the hard starts when the engine is hot.
I just want people to stop buying Air Temp sensors! It won’t fix it, I promise!
But people have replaced the coolant temp sensor too and it still does not solve the problem. I don’t think there is a definitive solution to this problem yet.
Well, almost two months have gone by, with the sensor unplugged. My gas mileage seems to be steady, around 28mpg. I did have to replace my left ball joint went it failed on me pulling into my driveway, but that’s another story…
I have had the same experience of many in this thread. 96 Tacoma 2.4L Two summers ago it began having difficulty starting when the engine was hot- I would drive around for a bit, stop, go into a shop, come back 10 minutes later and the engine would not start. It would crank happily, the plugs were getting spark, sometimes it would sound like the engine was almost going to catch, but no joy. After 30-45 minutes of being off, there was a good chance it would start again, but I still crossed my fingers.
Like many here, I popped the hood and fussed with a bunch of stuff. Got on line, read some blogs, tried a bunch more stuff. Just like everyone else, I discovered that disconnecting the air temp sensor (in the air filter box) let the engine start right up, but wasn’t satisfied with the process.
I did finally (last summer) get around to unscrewing the Mass Air Flow sensor (sitting on top of an aluminum coupler right behind the air filter box) and discovered that the leading sensor (there are two) had dirt all over it. I sprayed both sensors thoroughly with Brake Parts Cleaner, probably 1/2 the can (it’s what I had handy, I would recommend getting MAF sensor cleaner if you can) and have not had a problem since. On the hottest days (110-115 F) it may take 4-5 more cranks to start than in the winter, but that sure is better than 45 minutes waiting or $600 for a new MAF sensor.
I hope this helps everyone else who is having this issue. The MAF sensor is very easy to access, you can remove it with a screwdriver (2 screws) and a quick peek at it will let you know if you are potentially dealing with build up on the sensor throwing the computer off, or if your experience may be caused by other issues.
we had the same problem with a 1995 toyota tacoma it would not crank when it got hot my husband had replaced the fuel pump, coil, fuel filter, and unplugged the sensor , you need to try the fuel pump relay it help ours.
When you disconnect the temp sensor your ECU assumes the engine is cold and bypasses (ignoores) the upstream oxygen sensor output in order to allow the engine to run rich. You may want to check your oxygen sensor output next.
reroute the fuel line and filter to rear fire wall. I did this and never had a problem again. The fuel line and filter are located on driver side mounted to engine block. This is not a great place for the fuel line and filter. As we all know aluminum blocks burn hot and do to hot temperatures were ever u live causes vapor lock (fuel gets to hot). To reroute fuel line and filter i had to get a custom line made but this solved the problem
Me to. I discovered that if I raise the hood & leave it up until I want to go it starts.
If I don’t raise the hood & no start. I pull the FIA sensor out of the air chamber, cup it in my hand & pour cold water on it, hold it for about 5 seconds, lay it down wherever and the beast will start every time. Another idea is to park on a slight hill, let err roll to 2 to 5 MPH, key on 2nd gear and release clutch. Seems to work every time. I tested the FIA sensor - test good.
Where to next? Ideas are like opinions. Everyone seems to have one.
I suggest you try spraying some starter fluid into the intake when this trouble happens again. If that seems to work okay then I have to wonder if the ignition system output is degrading somehow when things are hot. Perhaps a weak igniter.
I had some discussions with a couple of my friends, One is my Saab mechanic. He tells me that he knows more probably about the Toyota than anyone else in town.
The other friend is a real friend. I told him that I did the recommended test on the FAI sensor and the ranges of resistance were compatible. I have installed a 350 resistor in series with this sensor.
When cold it has about 2000 ohms. When hot it has about 1000 ohms. The purpose of this sensor is to track the temperature and restrict the amount of fuel sent to the engine as it becomes hotter. By putting in this resistor it should realistically impede my MPG. I’m only getting 21 MPG anyway.
What kind of mileage do you feel you should be getting? Was the question. I have been reading that people are getting 28 MPG, ‘or are they just blowing smoke?’
I installed a 350 Ohm resistor in series with the FAI sensor. Now it starts every time just like brand new. At last it is a lot of fun to drive my Taco.
I did a fuel fill-up today, took a snapshot of the odometer and checked the millage for the past 10 1/2 gallons. It showed 20.25 MPG.
Obviously I’m not looking forward to the next tankful but I am anxious to know what difference a little more enrichment of fuel will make on the MPG.
I would love to share a photo or something but that will be a real PITA.
What kind of mileage do you feel you should be getting? Was the question. I have been reading that people are getting 28 MPG, 'or are they just blowing smoke?'
28mph…MAYBE down hill with a tail wind. Even with the small 2.4l 4-cylinder is only rated at 21/24mpg…If you do ALL HIGHWAY driving then you should get around 24.
Oh well,
Smoke will be smoke. Back to my hard starting problem. After the monsoons were over here in Southern Nevada the temperature is on the way back up to a reasonable heat of around 100 degrees. First day out with the larger resistor, I had a problem. I put in a 550 ohm resistor. It started a few times, but then the sun got a little warmer. No Start.
I keep hearing that if the sensor is unplugged it will start. Makes sense. To prevent leaving the sensor unplugged, I have come up with the idea of a switch to temporarily unplug the sensor.
To do this I am acquiring a spring loaded off toggle switch and locating it in side where I can reach it with my left hand to hold it on while starting when the vehicle won’t start when hot.
I know I’m am not the most intelligent guy on this circuit. That jerk has figured this out already but is too cute to share it with us less unfortunate.
I have to say, adding a resistor to the circuit to make the system think it is colder than it actually is makes me want to shake my head a little but it does seem to work from results you say you got. Have you checked the voltages getting to the air temperature sensor to verify they are what they should be? The voltage across the sensor should change with the air temperature changes (you did state earlier the resistance does change). Have you also checked the wire connections between to the ECU and the sensor for any problems like bad connections or bridging to another circuit?
Does this vehicle have a separate coolant temperature sensor for the ECU to use and if so have you checked that for proper operation?
I don’t know why this is the first time I have seen this thread, but not knowing Toyota trucks, I have to ask if they have an aux electric powered cooling fan? I’m pretty sure that there is a belt driven fan with a clutch, but I have heard somewhere that they may also have an electric fan for some conditions.
The reason I bring this up is that if there is an electric fan, there also may be a relay and a timer that will turn on the electric fan if the coolant temperature rises above a set point within a set time after the engine is shut off. If that fan is not working for any reason, relay, fan motor sensor etc, it would cause a hot start failure.
Just something to look at, as I said, I am not familiar with Toyota trucks. I do know some cars that have this feature.