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Kyle N.
Kyle N., Toyota Technician
Category: Toyota
Satisfied Customers: 5229
Experience:  ASE Master Auto Technician, L1 certified, CA. Smog Lic.
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Hello, Im having a problem with my 94 4runner (3vze) running

Customer Question

Hello, I'm having a problem with my 94 4runner (3vze) running very rough and/or dying after it is restarted warm. ie it starts and runns fine when cold, but if I go to the store and come back out and restart it it seems to want to die. If I rev the engine up to about 2500 rpm for 20 seconds or so it It will come out of it and run fine again.
Submitted: 8 years ago.
Category: Toyota
Expert:  Kyle N. replied 8 years ago.


Is the check engine light coming on at all?

Customer: replied 8 years ago.


There is no Check engine light or Diagnostic code associated with this problem. 1994 Toyotas are pre OBDII diagnostics.

If anything I think it could have something to do with the "cold start injector" opening when the engine is already warm and creating an overly "rich" condition until the coolant circulates back to whatever sensor is controlling that function.

Expert:  Kyle N. replied 8 years ago.

Hi again,

I know it's pre OBD2 but it still has codes and a check engine light. The cold start injector usually stays on because the coolant sensor is giving a false reading to the computer. If you want to see if this is your problem get it warm then shut it down and unplug the cold start injector and see if the rough running condition goes away. Let me know if you need more help.

Customer: replied 8 years ago.
I'll try that and get back to you. Now that you say that I wonder, during my last round of repairs I had to drain the coolant, could I have an air pocket in the cooling system possibly causing the sensor to give erroneous readings to the ECM?
Customer: replied 8 years ago.

Hello Kyle,

I tried that idea, but unfortunately the was no change with the cold start injector unplugged. Now I'm definitely confused. This thing has no other problems anywhere, except just this certian warm start issue. Whatelse can you think of that would cause this problem.

Expert:  Kyle N. replied 8 years ago.

I would check that the thermostat isn't sticking. When it's fully warm both hoses should be relatively the same temp.

That would cause it to think it's falsely cold.

Customer: replied 8 years ago.

Hello Kyle,

Sorry I haven't got back to you yet. I did check the upper and lower hoses with my infrared temp gun while the engine showed to be fully warm. The difference between the two hoses was only about ten degrees. I wouldn't think that was enough of a difference to indicate a thermostat problem. I'm going to replace the temp switch and make sure all of the air is out of the cooling system and see if that makes any difference. (I worry about air in the system because all three coolant temp senders are above or at the same level as the top tank of the radiator and are located on the backside of the engine.)

At this point, just as soon as either you or I figure out what's causing this problem I will make sure you get paid the deposit I have put up for your time. If you can think of anything else that could be causing it to have a very rough or dying idle only after a warm restart, please let me know.

A further note; it seems like this problem occurs most often when the engine is restarted within 20 to 30 minutes after shutting it off fully warm. So far the elapsed time and engine fully warm are about the only common denominators I've been able to pin point that corresponds with this problem.

Other info about this vehicle;

Mileage about 219,000

Reman long block installed around 125,000

Trans rebuilt around 150,000

I took possession 171,000 with blown head gasket

Heads resurfaced and pressure tested, new head gaskets, timing belt, timing belt tensioner and idlers, water pump, and thermostat all installed @ 171,000.

New engine control wiring harness installed around 179,000.

Valve clearance re-shimmed around 204,000

Engine driven fan removed and thermostat controlled electric fan installed around 217,000

218,000 new valve cover gaskets, 6 reman injectors and 6 spark plugs installed, first of three coolant senders replaced, new fan idler shaft(also known as water pump bracket) installed.

Now after seeing some of the history, it might help you to know, this problem has been evident for more that 2 years although not as severe as it has become just after this last round of repairs. Before it would want to run rough for 20 - 30 seconds when restarted warm but it would very seldom die. Now it will idle so rough that the idle will drop to below 500 rpm in neutral and then die if I don't immediately rev it up to about 1500 - 2000 rpm. If I hold it at that rpm for 20 - 30 seconds, then I can let off and it will return to a normal idle again.

I hope I've given you enough information this time to get a clearer picture of what's happening. I know it can be hard to determine the problem without actually seeing the vehicle or this type of problem on a similar vehicle.

I look forward to your next suggestion.



PS: I've upped the offer to $25.00

Expert:  Kyle N. replied 8 years ago.

Hi again,

10 degree difference in the coolant hoses is normal. Something I noticed about your reply. Getting the air pockets out of the cooling system is important on your engine. You have to remove one of the heater hoses off the firewall then fill the radiator until the coolant comes out of the heater hoses. Make sure the heater is turned on before you start. That may just fix up your problem.