Drtomcat

Hi all, this is my first time using a forum so please bear with me. I have a 2000 4Runner with 230,000 miles. Over the past few weeks it has been dying on me while driving. Usually it dies when I'm slowing down to stop at a light or already stopped and just idling. However, it has also died when I'm just driving at different speeds.... I've done some troubleshooting and I cleaned my throttle body, idle air control, and mass air flow sensor. That fixed the issue for a couple of days but then the problem returned. I checked the fuel pressure (which was a pain in the ass) and it was a bit lower than it should be. So I dropped the tank and replaced the fuel pump. Well that fixed the problem for about 20 minutes and then I'm right back where I started. It's also worth noting that I replaced the fuel filter less than six months ago. Oh yeah, it's not throwing up any codes either, no check engine light, nothing... I'm desperate haha please help!!!

HELL4CIOUS

Did you check the fuel filter again(even if you just replaced it) and fuel lines, It might be that you may have a clog. Worst case scenario, and god forbid, you maybe put diesel in it instead of gas(happens and it shows similar symptoms), but I would check all fuel lines first, only take a little to get clogged..

Drtomcat

Thanks for the response Hell4cious. I haven't checked the fuel filter since I changed it. I don't think there are any flow restrictions in the fuel lines though because when it is running, it runs very smooth including at idle.. Definitely haven't put disel in it either. I've been reading a lot of other similar threads though and I'm seeing the IAC as a common solution..I cleaned it out already (it was really dirty) but I haven't checked it out electronically (resistance or voltage).. maybe I need to replace that..

HELL4CIOUS

One more thing that I would check is if the fuel pump is not losing power or shorting out electricity wise. You may have a electrical issue.

Drtomcat

Thanks for the suggestions. I checked the fuses and nothing is blown.. I'm beginning to wonder if fuel isn't the issue. I heard that a crankshaft position sensor could cause intermittent engine stalling if it was producing a weak signal..I think I may look into that

HELL4CIOUS

Are you getting a legit check engine light or is it just shutting off and back to normal. With CPS it usually throws a check engine light and most of the time it will restrict rpms at top end or won't turn over at all. I really don't know what to tell you other than the CPS is also not a very sensitive sensor and is one of those sensors that will kick in mostly right before the thing its sensing is about to blow up and is mostly accurate in reporting a real issue so pray its not it. Did you check the Throttle Positioning Sensor and the throttle body/cabling and the vacum hoses/sensors?

Drtomcat

No check engine light. I agree that the CPS should throw a check engine but I'm running out of ideas. I haven't checked any vacuum lines out sensors yet though. If I had a vacuum leak could it cause intermittent stalling?

Drtomcat

Oh and I actually replaced the TPS less than a year ago because it threw up an engine code for it. After replacing the TPS, the check engine light went away. That was one of the easier fixes I've had to do.

HELL4CIOUS

Yes, it would cause stalling while at lower RPM's like at a stop light or so. I mean shoot, I fits not throwing codes, then from my experience I can safely say it has to be air/fuel delivery, but even then by the sounds of it you might be spending a lot of time searching. Honestly, If I where you, I'd bite the bullet and spend 85 to 100 at the Toyota dealer and get a Inspection/diagnosis. But check all these first.....if not then dealership. Oh, almost forgot, is it backfiring?

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* An engine vacuum leak. Check for loose or broken vacuum hoses, leaks around the intake manifold gasket or throttle body, leaks around the PCV valve and EGR valve.

* A dirty or defective airflow sensor. A sensor that has been contaminated by fuel varnish or dirt will under report airflow and be slow to react to changes in airflow. This can upset the air/fuel mixture causing idle, stalling and hesitation problems. Cleaning the airflow sensor wire with aerosol electronics cleaner can often restore normal operation and cure the problem.

* A defective idle speed control system. Idle speed on a fuel injected engine is controlled by allowing a small amount of air to bypass the throttle. If the idle air bypass circuit is plugged with dirt or fuel varnish, or the solenoid valve is sticking or broken, the engine may not get enough air to idle normally causing it to stall. Cleaning the idle air bypass circuit in the throttle body with aerosol throttle cleaner will often remove the gunk and solve your stalling problem. If a good soaking with cleaner fails to fix the stalling problem, check the wiring connector. It might be loose or corroded. If no wiring faults are found, you may have to replace the idle speed control solenoid.

* A faulty coolant sensor. If the coolant sensor is bad and tells the PCM the engine is colder or warmer than it really is, that can screw up the fuel mixture, too. If the coolant sensor reads colder than normal, or cold all the time, the engine will run rich. This won't cause cold stalling but it can make for a rough idle once the engine warms up, and it kills fuel economy. If the coolant sensor reads warmer than normal, or reads hot all the time, the PCM will lean out the fuel mixture too much, causing the engine to stall when it is cold. See the article on coolant sensors for how to test the sensor. Replacing a defective coolant sensor will cure this cause of stalling.

* A faulty air temperature sensor. This sensor tells the PCM the temperature of the air entering the intake manifold. The PCM needs an accurate input so it can balance the air/fuel mixture properly. Just like a bad coolant sensor, a bad air temperature sensor can upset the fuel mixture causing stalling problems.

* A bad Manifold Absolute Pressure (MAP) sensor. This sensor monitors intake vacuum, which the PCM uses to determine engine load. If the MAP sensor is not reading accurately, the PCM may add too much fuel or not enough, causing the engine to stall. See the article on MAP sensors for how to diagnose this sensor.

* Low engine compression. If your engine has a lot of miles on it and compression is low because the piston rings and/or cylinders are worn, ot it has one or more leaky valves, it may not have enough oomph to keep idling. A compression check will tell you if this is a problem or not, and if it is there's no easy fix other than to overhaul or replace the engine.

* Worn or fouled spark plugs. Ignition misfire can make any engine stall at idle. When the engine is running slowly, there is less momentum to keep it going, so a bad misfire may cause it to stall. If the spark plugs have not been changed in a long time, a new set of plugs and/or plug wires can restore a good hot spark and eliminate the misfire. A weak ignition coil or a faulty crankshaft position sensor may also cause a stalling problem.

* Bad gas. Gasoline that contains too much alcohol (more than 10%), or gasoline that has been contaminated with water or some other substance may not burn well and cause your engine to stall. If the stalling started to occur shortly after your last fill-up, suspect bad gas. The cure is to drain the tank and refill it with fresh gas from another filling station, or just use up the bad fuel (if the engine runs okay at highway speeds), then refill at another station when the tank is near empty.

Drtomcat

Awesome response. The amount of work it's gonna take for me to correctly diagnose the problem makes me wonder if I should just bite the bullet and get it diagnosed at the dealership...I really wanted to avoid that route seeing as they charge $150 for a diagnosis but at this point I just need to know exactly what the problem is.

HELL4CIOUS

Without spending a ton of time on a hit/miss method of troubleshooting, taking it in might me a good call.