Stalling at highway speeds, help appreciated

So I’ve owned this Tacoma for roughly a year and a half now and up until recently I’ve had no issues. But within the last few weeks or so I’ve noticed some hesitation upon acceleration, and some idle surging. I have no CEL, I’ve read the codes with two different code readers that I own and there are no pending codes. Yesterday was the worst symptom I’ve gotten yet, I was on my way home from work, and the engine completely cut out, then restarted within less than a second and then did it again a mile later. I was able to limp it home (at a slower speed in fear that something is seriously wrong) and drive it around town today with no issues. It seems that the load I put on it causes the hesitation, but the complete shut off has me stumped. I’m just at a loss as I thought it could be a loose ground, as I’ve been replacing some stuff lately. (Plug wires, Plugs, Alternator) but none of the connections I’ve touched are loose. I’m super confused and would appreciate any insight.

I also forgot to note that I had a P0171 code for a few days like a month and a half ago, but it went away randomly.

 

Clean your MAF. If it persists, do a fuel pressure test.

 

I figured that would be the best next step, I have yet to replace the fuel filter so that probably doesn’t help. I have a new MAF sensor on the way. I’ll update once I’ve done those.

 

The P0171 could be caused by a dirty MAF but with the stalling AND the lean code I would consider the fuel pump as the primary culprit. A fuel pressure test might show low fuel pressure or it just might show correct fuel pressure. This is one of those car issues that you just might have to wait till it "breaks" to be sure. Unless you are doing the work yourself putting a pump in "just because" is expensive.

 

Might be a long shot, but something to consider... My '03 once began these stalling issues mostly on acceleration. They also happened on highway. See if yours happen with acceleration even slight acceleration. Truck would die, I'd roll to shoulder. Sit, turn key and it'd start up. CEL would be on for a little while then go out. Problem was throttle body, or some sensor in it that could only be replaced with complete TB. Again, may not be your issue but could be. GL~

 

I had this dangerous issue happen to me once long time ago on the freeway
Turns out a mouse or other rodent found its way into the air cleaner housing and had nibbled a hole into the element
Allowing unfiltered air to trigger the MAF and screw things up somehow with however that thing works
New air filter element and cleaning of sensor resolved that ish..

 

So little update, I installed a new maf, then pulled the efi fuse to erase the learning, and the idle dropped to like 480 and fluctuated to 530 every so often. I reinstalled the old maf and it went up to 650, but would slowly drop down. I also got the p0171 code pending again. Any ideas?

 

Clear all codes again and verify that there are no left over pending codes and drive it again, if the P0171 is still pending I would check fuels trims at idle. What scan tool are you using?

 

Vacuum leaks?
Then I would do what Glamisman says

 

I’ll definitely give clearing the codes a go again in the morning and driving it tomorrow, if my fuel trims are way off would that indicate a vacuum leak? I have a Bosch scanner, I have a little Bluetooth one as well but I prefer using the Bosch.

 

Yes. Hopefully on your scan tool you can look at what the MAF is reporting as air flow at idle in g/sec. The typical reading is 1 gram per second of airflow per 1 liter of displacment so a 3.4 should show ~ 3.4 ish g/sec. Most scanners have the capability to change display outputs. Trying to do the math from lbs per sec to g/sec is a pain. If it is way off that is a problem. Fuel trims, in a perfect world +- 5 to 10% is normal. Any posative number is the engine control unit (PCM) adding fuel which could indicate a vaccum leak or an exhaust leak before the oxygen sensor. If your tool has graphing capabilities it makes things much easier, you can take her for a drive and not have to continually look at the screen. As you accelerate there is a greater demand for fuel and if the trims get pegged at 25% plus that is an indicator that the PCM is trying to increase fuel volume, it can only do this so much and if the demand exceeds the capability a code is set, P0171. It doesnt take too much of a questionable fuel pump to do this.

Take a can of parts cleaner and mist it over the intake manifold, upper and lower, and listen for a change in rpm. Take some pliers and squeeze the vacuum line from the brake booster to the intake manifold and see if that changes the idle speed. Spray where the upper intake meets the lower intake. The factory gasket is a 3 piece metal gasket for a reason, aftermarket fibre ones will pull through and cause vacuum leaks.

The problem is as you have discoverd is that of a half way diagnosis. Fuel pressure should have been checked and on Tacomas it is a pain in the rear so most techs dont do it, they just recommend a pump. Toyotas are very particular when it comes to fuel injection parts. This forum is filled with people replacing fuel injections parts, MAF's, MAP's, injectors etc. with non factory parts and spending days chasing their first issue and newly created issues because the parts they put in are bad. Get you parts from a toyota dealer. There are many parts avalible on the internet that say Toyota on the box but they are knock offs.

All of the above is driveway doable, it just depends on your skills and your toolbox. Timmy the Toolman has EXCELLANT videos on all of this.

 

Symptoms sound like what my old 1980s toyota truck would do when it needed a fuel filter.
If it's cheap and easy to do on 1st Gen, it won't hurt to put in a new one.