Won't re-start when hot on warm days. 95 Toyota Tacoma

toyota
start
tacoma
sensors

#1

Like others, a 1995 Toyota Tacoma will not re-start when hot on warm days. It won’t restart 5 to 30 minutes after turning the engine off. If I park in the shade or raise the hood it restarts soon.



I discovered disconnecting the electrical lead to the temperature sensor in the air cleaner box allows the car to restart and perform normally. I replaced the sensor with a new one from the dealer but the problem continues. My current temporary solution is to drive around with the air temp sensor disconnected. I’m not aware of adverse results, but I’d like to find the real long-term solution. Also replaced the coolant temperature sensor and added an additional grounding wire between the engine and chasis. THANKS for any suggestions.


#2

“temp. sensor in air cleaner box”? Sure that’s not a MAF sensor? A friend of mine’s Honda did same thing, if I remember correctly it was fuel related, like a relay or something.

If it has an EGR valve I’d check it. For a short time, my '96 Taurus would do the same thing. I’m trying to remember if it was EGR related or something else.

Not sure if I was much help. Sorry.
Good luck, buddy.

JP#3


#3

1st you need to find it you are not getting fuel or spark.Try spark checkers or timing light will show if you are getting spark. Starting fluid will tell you if it is not getting fuel.
Air temp sensor can be tested with ohm meter.


#4

BOTH (old & brand new) air temp sensors appear to be working. High resistance when cold lower resistance when hot. About 2,000 ohms at about 70 degrees for both. Drops to about 1,000 ohms in hot water.

Getting both spark and fuel. I believe that the fuel being supplied is too rich and flooding the engine.

My understanding is that when the coolant temp sensor and air temp sensor are within 15 degrees the computer assumes a cold start, which requires more fuel. I believe that the heat from the ashpalt combined with the heat from the exhaust manifold plus the sun on the hood warm the air temp sensor significantly and the coolant temp sensor cools slightly resulting in them being within 15 degrees. This causes the computer to assume cold start and flood the engine. What I don’t understand is why this rarely happened in the first 250,000 miles and is happening regularly now. There has to be a fix.


#5

Have you tried holding the accelerator to the floor when cranking to try and clear a flooded condition?

Fuel may be leaking into the cylinders after shutoff.

The starter cranks normally but engine won’t fire??


#6

Somewhere around halfway to the floor is where the truck starts the fastest.

Correct, truck cranks normally but won’t fire.

I have a temporary fix that works 100% of the time. That is simply disconnecting the temperature sensor in the air filter box. I’m trying to find the correct permanent solution so that the truck starts quickly on the first crank.

I believe what is happening is the heat from the ashpalt, exhaust manifold and sun on the hood all increase the temperature of the air in the air filter box. My understanding is when the computer senses that the air temp and coolant temp are within 15 degrees it assumes a cold start. By disconnecting the temp sensor or lifting the hood, the air temp sensor sends a lower temperture to the computer and it adjust the fuel injectors for a warm start.

The question is what got out of specs so that this is a constant problem after 250K miles and 15 years of perfect service. Both the air and coolant sensors are new and had no impact on the situtation. I added an additional ground wire from the engine to the chasis in case there was high resistance as that would lower the temperature reported by the coolant temp sensor.

I’ve spent about $1,000 on this issue and leaving the air temp sensor disconnected is the closest I’ve gotten to a solution. I’m ready to move the air temp sensor to where it senses the true ambiant temperature opposed to that under the hood. But that still wouldn’t explain why this issue developed.

I’m also interested in see if other that had hard to start when hot issues get temporary resolution by disconnecting the air filter temp sensor.


#7

Hello there.

I too have this problem and have not found a fix either. 1995 2.4L 200k. I have replaced the coolant temp, no luck. Luckily I found similar forums on items that others have replaced which kept me from throwing parts at the truck.

For you Icare, unplugging the air sensor works, didn’t for me but oddly enough what will let me start every time is using a small pair of vise grips pliers to pinch the fuel return line at the fuel pressure regulator. For some reason when I pinch the line it starts. It made me think the regulator was stuck open or faulty allowing fuel to flow freely through the return line while trying to start. I replaced it and nothing! I wonder if the ECM is the cause? Either way I promise to return if I find something before any of you.


#8

I have a 4cy 96 Tacoma with 160k. Same thing. I started noticing it last summer but this summer it has been worse. Sounds like everything I have tried or thought of trying has already been done. I will be watching this space regularly to see if someone comes up with a solution.

Icare, I think you are on the right track. I have noticed the problem is worse in the middle of the day if I am in the sun. I have not noticed this problem nearly as much in the evening when the sun is low or set.


#9

Sorry if I did not follow well your posts, but could you please disconnect the wire for the cold start injector to see if the condition persists ? Please post your results.
the added attachment may help you.


#10

After doing everything mentioned in these posts, I’m wondering if the fact that all my heat shields have fallen off by now is the problem. That would account for it not starting until a year or two ago. I don’t know if it’s worth replacing the shields or if cooling down some other way is better.


#11

I’m having the same problem with a 96 T100 4 cylinder. I before reading this post I had to wait 15-20 minutes with the hood up any time the temperature got above 80 degrees and the engine was warm. Unplugging the air charge temperature sensor (which is good: tested the resistance and its fine ) works every time however, I too would like to find a legitimate fix. If anyone figures it out please post here.


#12

So far I have not seen the air flow meter/sensor operation of these trucks addressed. Unplugging the IAT sensor and blocking the fuel regulator return hose would both tend to richen the injection a bit. It might just compensate enough for a calibration error of the air flow meter to get the engine to start.

There does not appear to be a cleaning procedure for the air flow meter. There is an operational check but not a calibration check of the meter. Ouch, the air flow meter will be costly to replace on suspicion.

Keep us in the loop on this problem.


#13

So I just found the culprit to my truck’s problem. Same as above, would not start in hot weather once the engine was warmed up unless I disconnected the air temperature sensor (which works because i tested its resistance). First the check engine light has been on for years so I took it to see what it was saying was wrong. It had two faults. First was the air temperature sensor which I tested again and again it works fine.

Second the computer said the engine was running very lean. Checked all the vacuum hoses and all was good, next I pulled out the mass flow air sensor and right then and there I found the culprit. It had dirt all over the leading sensor built up about 1mm. Cleaned it with a can of solvent (specifically for mass air flow sensor) and reset the check engine light. Now it starts every time and runs better that it did before. Starts perfect in hot weather. Easy fix and did not need to buy any new parts. Not saying it is the same for everyone as many different symptoms have different causation…but worked for me


#14

I too have the heat soak issue where the vehicle will not start in warm weather about 20-30 minutes after shut down. My truck is a 1995 Tacoma 2.4. Cold start is fine as well. I have tuned the vehicle, changed the air temp sending unit in the air box and cleaned the MAF with isopropyl alcohol.

I agree with others here that valve buildup might be part of the problem. I recently ran a can of Sea Foam through the fuel system ($10 dollars at Kragen). Throttle response has noticeably improved. No way to tell if this helped cure the problem since the problem only occurs in warm weather.

I also agree with the others here that mention the heat buildup in the air box due to parking on hot asphalt.

So, if we can get the air temp sending unit to sense cooler temperatures (heck, just ambient might fix the problem) then the engine might start. My thinking is to remove the elbow that pulls air in from the wheel well. This might enable the air temp sending unit to cool down faster and fix the issue. They slip on to each side. Basically, friction fit with a few ridges in the plastic hold it on. You could also re-direct the elbow out or up. Not sure if there is room though…


#15

On the Toyota Tacoma, there is both an air temp sensor and an MAF sensor. The MAF is very expensive.

I have driven the truck since I posted the idea of removing the elbow and there was no change. We are in the middle of winter here in California and the temperatures are not very warm so the effect is very minimal. I really notice the issue in the summer between 15 and 30 minutes after the truck has been shut down.

I have since reinstalled the elbow.

I have not tried driving the truck with the air temp sending unit disconnected. I think it would open a circuit and trip a check engine light. But, if I get in to summer and the issue is again more pronounced, I might try that.

I also plan on running Sea Foam through the motor after 3-5k.

Update 1/22/2011. I installed a new EFI relay a few days ago. approx $30 on Rock Auto.
We had a few warm days here in California and the truck has not had any issues starting but that does not necessarily mean that the issue is resolved because I don’t normally notice the problem until the temperatures warm up and the truck has been shut down for about 20-25 minutes.


#16

Any new input regarding these issues? I have a 96 tacoma v6 4x4 w/221K mi. No problem like this until about a month ago (June-July 2011). I live and work in southern NM - use my truck for work outside. After driving 2 hrs to a field site and turning off engine, it wouldn’t start the first try after (1 minute?). Then started right up. I don’t seem to have the problem 10-20 minutes after like many of you do. My concern is that I’m working within a couple miles of US/MX border in remote areas…and it’s kinda important to have a vehicle that starts when you need it to (the other day I left it running all day from 8am until 6pm). It’s the same situation as described in these posts: plenty of spark, but something messed up with fuel aspect: too lean or shutting off. Temps where I work (outside) were about 90-102 degrees. As I said this is a new problem to this truck - it’s had absolutely no other problems since I bought it in Nov 1996. It’s lived it’s whole life in the desert (Mojave = 110 degrees, Chihuahaun = 100 degrees), but only since about 220K miles has this started to happen. Other pertinent info: I do not/have or ever had a “check engine” light come on for anything. My shop hooked it up but found no diagonistic codes/problems and could not reproduce the problem even after driving it 50 miles in 95 degree temps, and then letting it run for 2-3 hrs in their parking lot at 100+ degrees. The type of driving I do while working is stop and start every 0.5 mile to 1.0 mile…so perhaps there’s an aspect to air flow/volume and temp. There seems to be a connection with some of us with the 200+k mile age/wear of the vehicle. I haven’t checked anything mentioned here like cleaning the Mass Airflow Sensor, checking fuses, removing temp sensor… No one local here seems to have a clue and they tell me I need to wait until I have a check engine light come on…ya, right. any new suggestions?


#17

I’d try the $8. can of MAF sensor cleaner. aishahillbilly above states that worked for them.


#18

OK, I have done some more troubleshooting on this issue. I bought a PLX Kiwi to check MPG on my truck. It connects to the OBD II diagnostic port. The PLX Kiwi also pull the information that the ECU is receiving from the water thermal sensor unit.

What I noticed was that the temperature was spiking by about 25 degrees after shutdown on a hot day. I would shut the truck down at 186 to 191 and it would spike to 216.

Hence the term heat soak issue.

I don’t remember having this issue before I had the thermostat changed. I used to run a 170 degree thermostat and never noticed the issue. So, I went back to a 170 degree thermostat. So far, so good. The temperature spike only seems to be up to 190 degrees when shut down. Sometimes less. I used a Stant 48457 (usually for a Subaru) as it looked like the closest fit. Took a few hours of research to pick this one. The fit was better than I could have hoped for. It fit perfectly! I previously used an off brand and it also took me some serious time to find.

I installed the thermostat today so I need more time to test my theory.

On mine, the idle air control valve appears to be working fine because it reacts to the ecu’s command to allow more air when the vehicle is not up to running temperature.

Forgot to mention, I also cleaned the MAF again and there was no change in the symptoms. I took it in to a mechanic as well and the issue would not show itself while it was in his shop. He had it for days because of parts that were on order to fix a ball joint.


#19

Just bought a 1996 Tacoma 2.4L and it’s doing the exact same thing. I drive the tacoma all day as a courier, so it’s a pain to have to turn off the engine knowing it won’t start on the first try. Unplugging the air temp sensor will allow it to start the first crank every time with no problem, so this is what I do if I have to shut off the engine. I always plug it back in after it starts.

I will inspect the MAF for dirt buildup and report back here with what I find. Have not checked the coolant temp sensor yet.

6:06pm
Looked inside where the MAF sensor resides. Pretty clean in there, no dirt buildup. I might get a new air temp sensor and test it out. Those things are around $50 though!!!

Next Day:
Bought a new air temp sensor, installed it, but it did not fix the issue. I think it’s directly related to this sensor because it starts right up when unplugged. Been reading the shop repair manual for this vehicle and it seems it’s a known issue. Here is a link to the PDF for the manual:

http://www.ncttora.com/fsm/1996/96_repair_searchable.pdf

Read pages EG212-EG218 and you will see DTC (Diagnostic Trouble Code) P0110 “Intake Air Temp Circuit Malfunction” and DTC P0115 “Engine Coolant Temp Circuit Malfunction”. It also implies the ECM, so that might be the problem.

I think I will take the truck to autozone or a mechanic where they can hook up the computer to it and see what trouble codes show up. I will report back.


#20

Took the taco to autozone and they hooked up the OBD2 and it gave me two error codes, P0110 (Intake Air Temp Circuit) and P0401 (EGR System Fault).

Well, my next step is to clean the vacuum hoses I guess. See if anything is built up in there. Running out of options…