Help! My 99 Tacoma 3.4 is Running Rich: Here is What To Do Now!

Alright, gearheads, gather ’round. I’ve got a story for ya – a tale of a 1999 Tacoma and a 3.4L engine that just wouldn’t play nice. This thing was running rich, and I mean really rich, guzzling gas like there’s no tomorrow and smelling like a refinery. I’m the original owner, by the way, and this truck’s been good to me for over 90k miles, so I was determined to get to the bottom of it.

First thing I did was I checked the obvious stuff, you know? I swapped out the spark plugs and wires, thinking maybe they were just old and tired. Nope, not it. Then I moved on to the throttle body, gave it a good cleaning, and even cleaned the Mass Airflow Sensor (MAF) while I was at it. For a hot minute there, I thought I’d nailed it. The check engine light went off, and the truck ran like a dream… for about 50-100 miles. Then, bam, right back to square one. It was idling rough, and when I pushed it past 4000 RPM, it started backfiring like crazy.

Help! My 99 Tacoma 3.4 is Running Rich: Here is What To Do Now!

So I started digging deeper. Someone told me it could be the stick coils, so I changed those. Still nothing. I was starting to feel like I was chasing a ghost here.

Now, I’m no master mechanic, but I’m pretty handy, and I’ve learned a thing or two over the years. I knew that a rich-running engine could be caused by a bunch of different things, one of them being a bad oxygen sensor. So, I hooked up my trusty multimeter to the O2 sensor and took a reading. Sure enough, it was showing more than 450mV, which, if you don’t know, means the engine’s running rich.

But here’s the thing. I read somewhere that if it’s running too rich, it will also hesitate to accelerate, and mine is running great until 4000rpm. It would also show signs of getting worse over time, and I had just done a bunch of other work on it, so I wasn’t totally convinced that was the problem.

Then, a buddy of mine suggested I take a closer look at the start circuit. He said that the start circuit gets the relay engaged initially, and if something’s wonky there, it could be causing my issues. I have no idea if he was right, but it was enough for me to start poking around there next.

It’s been a real head-scratcher, this one. I’m still working on it, but I’m not giving up. I’ll keep you guys posted on my progress. Maybe one of you has had a similar experience and can shed some light on this for me. Let me know in the comments!

Help! My 99 Tacoma 3.4 is Running Rich: Here is What To Do Now!
  • Changed spark plugs and wires
  • Cleaned throttle body and MAF sensor
  • Changed stick coils
  • Checked O2 sensor with multimeter
  • Considering start circuit as a potential culprit

Still figuring it out, will keep you updated!

Original article by the Author:Williams,If you intend to republish this content, please attribute the source accordingly:https://www.suntrekenergy.com/6632.html