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Won't Start When Hot - SOLVED!

134062 Views 43 Replies 20 Participants Last post by  bharty
I am so damn happy!

I was here a couple years ago with a problem I just could not get solved. My 1996 2.4L Tacoma would not start when hot. After operating at temp, and leaving it for 10-20 minutes it would not start. It cranked hard, but would not start.

Searching the Internet I have found its not such an uncommon problem. I have seen many, many suggestions, but no one who actually solved the problem. I think I got 40- 50 replies here

After several years, many threads on the Internet, and thousands of dollars (I do not want to admit how much exactly). I took it to two Toyota dealers, and several auto electric shops. To be fair to my regular mechanic, he repeatedly told me not to throw parts at it. He told me to get rid of the truck. I refused. I bought a new daily driver, but kept the Taco and kept throwing parts at it.

I finally found a partial fix. Disconnect the air sensor and it starts every time! This may seem painfully obvious, but I replaced the air sensor early on, and that did not help, so I crossed it off the list.

Disconnecting the air sensor causes the CEL to come on, but I think I can figure out a permanent fix from here. Maybe the MAF?

Anyway, this opens the door to even great insanity. I had always wanted to do a complete rebuild with new engine, Tranny, suspension and paint job. This stupid problems was all that was holding me back.

At least some of the parts that I threw at it will come in handy, like a new radiator, injectors, fuel pump. (Got an extra ECU, if any one needs one)
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Maybe since it runs better without the air sensor plugged in, that's probably the problem.... just a thought!:p
I honestly have this exact same problem with my 2.7L. I can guarantee that something is becoming heat soaked when the engine sits for 5-25mins after being at operating temp.

If I stop it and start it again like a minutes after I did it will fire up with one crank, if I leave it for 5 or longer it takes a solid 10 seconds or longer of cranking to catch fully. If I start it when cold or not up to operating temp it fires right away. I'm just thinking that the coolant is leaking back from the hot head to the coolant temp sensor, heat soaking it and causing it to run a rich start up. I've checked the sensor and all the resistances seem to be within spec. I just think its a combination of a bunch of things since the engine has 300k km. Stuff like injectors not perfect anymore, sensors a little off, a bit of carbon build up, are all just a factor.

Today it was acting up real bad though, since it was a hotter more humid day too. Cold days are never an issue at all. I'm going to hook up one of my widebands from my car and see what its reading while its cranking.

and damnit you wrote solved like you had actually solved the problem! but you haven't. I was all excited when I saw the thread title.
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My 96 2.7 had the same thing going on and I took the mass air senser out and the wire's were dirty, so I sprayed it with b-12, wire's only. The problems been gone for a year now.
O.K., here's what's going on.

There are certain things needed for the computer to make the motor run and stay within the allowable emissions.

The air flow sensor, temp sensor, crank position sensor, and probably several others fall into this category.

These are the sensors the computer uses to adjust the fuel mix.

If one of these fails, the system goes into a "Limp Home" mode. When this happens, the computer sets everything to a default and delivers a set amount of fuel and spark timing.

This fixed map does not account for or make adjustments for temperature or anything, and will not meet emissions requirements, but the truck WILL run when it's like that. It's probably too lean, or too rich, but it's close and it runs.

The idea is to avoid stranding you in the middle of nowhere because your air flow sensor plug came loose.

So, what's happening is you are throwing the truck into limp home mode by pulling the airflow sensor out of the circuit.

Naturally, it starts. That's what it's supposed to do.

Now, you need to find somebody that can diagnose that truck and find out what's wrong with it.

It's probably not the airflow sensor. (You said you replaced it, right?)

Somebody needs to hook that baby up to a real diagnostic scanner and look at what's going on when it's in the no start condition.
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It seems the 95.5-97 trucks have this problem alot.. My 96 2.4L does the same thing. In my searching, it seems that those years are the ones always mentioned. My 99 2.7L starts 1st time, everytime.
Sorry Crazy! But it is kinda solved. At least I can take my truck around town for errands on the weekend and not get stranded in some parking lot. Summer temps here in the San Joaquin Valley can run over 100 F for days, so getting stuck in a parking lot is not fun!

I used to vacation in the California High Desert, and that has been out of the question for years.

I kind of hate to write this becuase it shows how crazy I am am, but after the frustation I endured I want to help others with the problem, so here is a list of parts that I threw at it:

Fuel pump
Fuel Pressure Regulator
Crankstaff Postion Sensor
Ignitor Module
Fuel Relay witch
Distributor Coil
Heat Shield
Air temp Sensor
Throttle Body Sensor
Coolant Sensor

Fast Frank, I do think it is in limp mode, and I think its going to use a lot of gas.

But NOTE that I disconnected the AIR TEMP SENSOR, not the MASS AIR FLOW SENSOR (MAF). I do not think it would run without the MAF.

Boonie Buster, please note that both the Air Temp Sensor and the Coolant sensors have been already been replaced.

Rambo, note that the MAF is the one part that has not been replaced, I hope that is the problem. I read someone else who said that solved the problem for good. I am going to get around to cleaning, or replacing that this week.
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Looks like the Mass Air Flow Sensor is a $5-600 part! Not even sure that is a Denso part.

Going to get it checked and tested on Thrusday before I just throw that part at it. But if that is the problem, I will spring for a new one
Clean the MAF first its easy. A lot of people put freshly oiled K&N type filters in and it gunks up the fine MAF wires inside.

I cleaned mine and a lot of people said it solved their starting problems, but mine are still kicking. haha When you say the wires were dirty, you mean the plug on the outside of the MAF or the wires on the inside of the maf? Whats B-12? Other than the vitamine your body needs to function.
Crazy, that is a very interesting comment about the K&N filter....makes sense...

I seem to recall this started about the time I installed a K&N filter in the air filter housing....

I later intalled the K&N Cold Air Intake kit, and a dual exhaust .....

I did not mention that because others with this problem never mentioned mods before....

My mechanic says you can not clean the MAF without messing it up....

There is supposedly a special parts cleaner for the MAF, but I do not know exactly what it is....Any help? What is the B-12?

Anyway, I will get it checked tomorrow. I only drive my truck one day a week since I have a new daily driver

If its not functioning to spec, I will throw a part at it. Its an expensive part, but I am so deep into this already, I got to get it fixed.

It really runs rough with the air temp sensor disconnected, but at least I can get it started when I get stranded. Where I live, getting stranded in the heat can be dangerous.
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My mechanic says you can not clean the MAF without messing it up....

There is supposedly a special parts cleaner for the MAF, but I do not know exactly what it is....Any help? What is the B-12?

It is okay to clean the MAF with electronics cleaner and that can be found just about anywhere. Disconnect the battery, pull the MAF and give it a good spray down. Let it dry thoroughly before you start plugging everything back in.

This is what I use:
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The above will work, but if you're a perfectionist:

Also - MAF for 5-600$ !!! DAYUM!

Check here: I found the link whilst googling. $130+32 Core charge.

:dunno: Seems Legit? :dunno:

Good luck!
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I found a major clue!

I have found many cases of this in different forums. Almost all 95-96, and it effects both the 2.4 and 2.7 engines. The 2-3 cases where it was permanently fixed were by cleaning the MAF.

Guess what?

I looked up the Mass Air Flow Sensor, and it is specific to 95-96 and common to both the 2.4 and 2.7!!!!!

Why would they change a part like this if there was not a problem?

Crazy, what year is your truck?

Thanks for the tip on the cleaner, I will try that. If it helps I will go ahead and replace the MAF with a Toyota one. Just can nor afford to take chances when you play in Death Valley
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At less than $10 for a can I don't see why you are so convinced to replace the part out right. But than again it's not my truck.
If it works as an initial fix, just keep the bottle of cleaner in your tool bag for if/when :dunno:
Looks even deeper than I thought...Sounds like what the California Air Resources Board calls a "pattern failure" . The tech at Toyota got real defensive when I started asking questions

Toyota wants $776 for the OEM Denso part
One potential problem with the cleaner is that it may erode the coating on the resistor. I travel in the Eastern Sierras and High Desert. Places You do not want to get stranded
So buy 5 refurbs, one of 'em ought to work for yah! ;)

Re:"Toyota wants $776 for the OEM Denso part" / "I travel in the Eastern Sierras and High Desert. Places You do not want to get stranded"
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Whats the part number for a 96 MAF and the 97 MAF?

I couldn't wait so I went digging on one of the online parts stores I use.

When I look up MAF for my 96 2.7L I get part numbers

1)FIC1742202 and 2)FIC1753934



When I look up MAF for a 97 2.7L I only get part number


Obviously these are specific to this make, but I'm guessing two were available, and the later years they only used one of the two.

I'm gonna have to find out the difference in them.

More digging!

for 95-96 its

1)FIC1742202 and 2)FIC1753934



for 97-98 its only


For 99 its

1)FIC1742202 and 2)HIT1910771(just the sensor, no housing)



and for 2000 on its just

HIT1910771 just the sensor.

What are the extra prongs for??

and people are definitely getting screwed for 97-98 because you can just buy the sensor for 200$ less but if you choose 97-98 they make you think you have to buy the whole thing.

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I think the actual fuel system may have changed after 96? anyone have some ECU numbers to confirm this? It may not have to do with the MAF at all but more a complete fuel system overhaul after 96.
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