Okay...after searching YotaTech for days in hopes of finding a post that addresses the issue I'm currently having, I've resorted to starting a new thread. I've had my 1993 Toyota 4Runner with the V6 3VZ-E engine for about 10-12 years, currently just over 185,000 miles. The problem started about 3 months ago while I was on my way home from running some errands. My truck started up just fine, however, when I stepped on the gas pedal it was as if I had no power. Every time I attempted to accelerate resulted in my engine sounding like I was continually stepping on and off the gas pedal even though I wasn't. It was a very rhythmic up-down-up-down-up-down. I coasted along for about a 1/2 mile until I came to a stop sign...when I took off again the problem was gone and my truck resumed to running normally. I drove it for a couple of weeks with no problems and then out of the blue the same problem surfaced again. I kept giving it more gas in hopes of making it to my destination about 1/2 mile away. I did make it, however, I believe I flooded it out as it died as soon as I pulled into my parent's driveway. After letting it set for a couple of hours, I started it up and made the mile drive back home without any issues.

My son-in-law is an excellent mechanic and has always kept my ol' girl running. This truck is 25 years old and still had the original catalytic converter/exhaust system...he thought this might be causing the problem so he installed a new one. No luck, the problem persisted...actually, it seems like it may have made the problem worse. Now whenever I pull out of the driveway the engine starts revving up and down as soon as I step on the gas pedal, again like it's going to stall out. We've since installed a new Denso oxygen sensor, replaced the EGR valve vacuum modulator and the fuel filter. I believe my husband may have also replaced a portion of the fuel line near the fuel pump when he installed the new fuel filter...none of which have solved the problem. The last time we pulled codes we got 12, 14 and 21.

My husband doesn't want to keep throwing $$$ into my 4Runner looking for the fix, that's why I started searching this forum. I've read hundreds of threads on this site and have not stumbled upon anyone that seemed to be having the exact same problem that we're dealing with. After everything I've read, I'm wondering if it could possibly still have something to do with the catalytic converter, or maybe an issue with the fuel pump? Any advice from the 4Runner enthusiasts and Toyota techies that share their knowledge on this site would be greatly appreciated!!

 

WOW...where is everyone? I really don't want to take my truck to a shop for repairs. I trust the knowledge of all of you Toyota aficionados much more than any local mechanic!! PLEASE ...

 

Sounds like a fuel starvation problem to me. The fuel delivery system isn't able to keep up with the engine demands, so the engine starves out, until the fuel system catches up, and the cycle repeats.

You may have a dying fuel pump. Check the fuel pressure and the fuel delivery. There are some threads on this forum about how to do that if you search.

Back in the days of engine mounted fuel pumps, these were the classic symptoms of vapor lock. Modern tank mounted pumps don't have that problem, but when they go bad you could get similar symptoms.