High Mileage 5VZFE miss/running gremlin HELP!

Hi there,

I've got a 98 Tacoma 4wd, 5VZFE 3.4 V6, 310,000 miles on the clock. I'm the second owner, it only had 50k when purchased.

I've done very little to the engine outside of regular maintenance - timing belts, tune ups, oil every 3k, all the usual stuff. It's been a great motor, for the most part.

There is a mystery 'miss', for lack of a better word, which has been occurring over the last 8 months or so, and the miss is increasing in frequency. Hard to describe - going down the road at highway speed, and it feels like it doesn't get any fuel for about a 10th of a second, then goes away. It is not spark knock or a misfire, it just seems like a weird hiccup.

I've replaced all 3 ignition coils, wires, plugs, fuel filter, all of the usual suspects in the last couple of weeks, and to no avail. This hiccup just keeps happening. Everything else is working fine, no codes, only observable possible co-issue is that my fuel mileage has taken a bit of a hit the last few months as well.

I'm counting on this truck to keep going for another 100k or better, but this problem has me flummoxed, and of course every mechanic I've talked to hasn't been able to solve the mystery.

Anyone else have a similar hiccup/miss problem? I've looked around the web, and most info relates to misfires or problems with Idle Control, neither of which are relevant to this problem; at least I think they aren't.

 

I had the same exact problem ended up being partly due to the throttle position sensor, which did actually help it somewhat, but ultimately the real culprit was the fuel injectors. I had an injector that was slightly leaking and one that was not always opening fully. After pulling the injectors and testing their resistances there were a few that were outside of spec and two that were giving me the issue. I ended up getting a set of injectors that were perfectly within OEM parameters from a couple of different trucks in the junkyard for cheap. I think I paid about 10 bucks each and then sent those out to Witch-Hunter Performance to get them rebuilt and flow balanced.

The smoothness that returned to the engine and power I got from back was honestly unexpectedly noticeable.

 

what you describe sounds like a dirty or bad MAF as well. when i get symptoms like that i always clean the MAF and it goes away. doesn't have to throw a code to be a MAF issue. i had to clean the MAF constantly when i had a K&N filter. the oil in it attracts dust to the sensor which is just past it. paper filters work better for me. I'll say that i usually get better mpg with a dirty MAF though, but less power as it typically runs lean. seems to run counter to your problem.

 

Also, check ALL your vacuum lines to see if you have a potential leak starting.

If the lines are hard and not making a good seal this can be the start to your problems.

ANY VACUUM leak on this engines will cause issues

 

My 96 5VZ with 232000 miles has started doing the same thing! I had a ignition wire on cylinder 4 arc out few months back,and it just hasn’t idled or ran good since. I replaced wires, plugs, (with Denso dual electrode on driver side) NGK on passenger like they left factory. Cleaned MAF sensor, Checked my coil packs with multimeter. Seems to always do it very shortly after the truck gets to full operating temp.Truck seems sluggish going up hills at around 2000-2200 RPM but seems ok at other RPM? I expect it’s my injectors because seems everyone has injector issues around 220k to 250k. Thought about cleaning my throttle body and idle sensor to see if that would help.

 

Thanks for the tips, gentlemen, will look into all of these and get back to you with results.