Rough Idle then dies

I drive a 98 tacoma ext cab 3.4L and it has around 220,000 miles on it. My truck broke down on me on the way to work last week. It died when I was getting up to speed. I was able to start it up but it would idle really rough and die after a few seconds of rough idling. I have seen some threads regarding the IAC but I cleaned that a few months ago. Also, i just checked the fuel pump a few months ago and it's only two years old. I seen some other people saying it could be the Mass airflow sensor but its not throwing any codes at all. Also, the alternator is nearly brand new as i replaced that a few months ago when i checked the fuel filter and cleaned the IAC.

Looking for some ideas if anyone has any. Thanks

 

Check for air, fuel, spark, timing, and compression on all cylinders.

 

I’m on the same boat as you. Just completely died and now when cranking, need to give gas to keep truck running.

 

I am assuming that you have a OBDII code scanner because you said it isn't throwing any codes... she might have codes pending. If you tool can check for pending codes see what it says.

 

I had this problem myself...(well similar problem with rough idle and dying).... when I was driving and I would start to lose power. VERY rough idle and when giving it throttle it would barely rev and die. Ended up being a failing fuel pump.

 

My fuel pressure is good. Brand new fuel pump and filter.

 

Did you try cleaning the throttle body real good?

 

I will need to dig into mine more then. My scanner didn't show any pending codes. But also, when I would try and give it gas it dies as well. My truck is under a foot of snow right now so maybe this weekend I can get into it again. I hope its just a fuel pump. but i just checked it a couple of months ago.

FYI I recently fixed a shorted wire that was causing my EFI fuse to blow and causing my truck to die but it never had an issue idling. Also, i checked all of my fuses and relays. So far so good.

 

Just an update. I removed the fuel line from the inlet side of the fuel filter and tried to start the truck. No fuel came out of the line, just a little dribble. I can hear the EFI relay pull in and what sounds like the COR do the same thing under the steering wheel. If the relay had as short in the coil it would have blown the fuse, so I think I'm going to try the fuel pump soon. I have 220k miles, would it be a good idea to replace the entire sending unit?

 

yes and no on the sending unit... I have put a pump only in just to have the low fuel light portion act up a week later. Irritating to say the least.

 

So I have finally been able to look into this more, but no luck yet. I replaced the fuel filter. I used my meter and measured the voltage on my MAF. Ohmed out my TPS. Ohmed out my fuel pump. Applied voltage to the IAC to confirm its operation. Cleaned throttle body and IAC. Checked every fuse and relay.

The fuel pump isn't that old, but I dont have a fuel pressure gauge or know where to put one to see how much pressure it has either. It does pump fuel though.

Everything seems to be in spec according to the manual. I did notice that my fuel pump doesn't turn on until I actually turn the key over to start it. I thought the fuel pump came on with just the key on? It seems like there isn't enough fuel pressure to keep it running. It starts and sometimes idles a little over 1k rpm and then dies immediately. If i give it gas it dies or wont even try to start. Most of the time i start it, it tries to idle at 750 rpm and then dies but the longest i have gotten it to idle was maybe 3 seconds. Every other post I have found regarding this seems to be a mystery and nobody reports back. Another thing I noticed is I cant get it to throw any codes when removing sensors, but maybe it wont unless it actually runs. Any other ideas?

 

It has to go through a warm-up cycle before it will throw a code.

 

the fuel pump relay or as Toyota calls it "circuit opening relay" does not operate as you are thinking. There is no fuel system prime like in other vehicles so turning the key to the ON position does nothing for priming the fuel system. Only when the PCM receives a signal from the crank portion of the key or when the motor is actually running on its own will the PCM ground the circuit opening relay and the fuel pump will run. The "run" signal is received from the crankshaft position sensor and I believe that it is that signal you are missing. Does this mean that you need a crankshaft position sensor? Maybe, maybe not. You could need a circuit opening relay. The only way to tell is to locate the circuit opening relay and check for +12 volts on the Blue wire during cranking and when you let the key back to the ON switch position. Applying +12 volts to the blue wire should make the pump run all the time. You could do this as a test to see if the issue IS fuel related or not.

 

I had the same issues. Changed the ECU and problem solved.

I could not scan (linking error), checked all fuses, checked all sensors. My fuel was running rich. I had air, I had spark.

Try and check your ECU.

 

I have the bed off my Tacoma for frame rust.
My neighbor said I should replace the emission canister solinoid. If it's bad on yours it might be the problem.

 

Thanks for the help guys. I have some work to do it looks like. Where is the emissions canister solenoid located?

 

The emissions system won't cause the symptoms you're describing.

 

Thanks for the help everyone, just wanted to give an update. I went ahead and replaced the fuel pump and that fixed the issue. It started up like a champ. The one I removed was still working and even ohmed out within the specs of the manual, but it clearly wasnt supplying enough pressure.