Hey everyone,
99 4runnner v6 4wd automatic SR5
while cruising at 50mph and roughly 2000 rpms...rpms drop to 1200 and then jump back up.
Almost as if the runner turns off and turns back on.
intermittant problem and at times while on the hwy....a very violent , turbulent engine bucking happens.
Reminds me of when i had a fly stuck to the sensor on my mass air flow sensor.
very hard bucking and then it goes away for days.
No Check engine light.
Here are recent items done.....cleaned throttle body, cleaned mass air flow sensor after issue started.
** changed TPS sensor( not toyo brand) before issue started.
Plugs changed after issue started.
Anyone else had similar issues?? Thx !!

 

Are you getting a CEL? Violent bucking like that sounds like a coil or injector misfiring, or rather NOT firing.

 

No Check engine light.
i was thinking coils as well.....hopefully!
any idea how to test those? Thx.
The rpm drop is deadly smooth.....almost like turning the key off and then back on. The tack drops 600 rpms instantly and then back up. So its not like taking your foot off the gas and it gradually declines. This is instant.

The highway bucking is rough as heck.
i 've had a bug on my mass air flow......that made the truck buck and run very strange.

 

Coils you can test with a digital multimeter. There are specs in the FSM for resistance between the two pins, and from each pin to the electrode.

the more you describe it though, I’m thinking it could be a TPS going bad. That you can test with a multimeter as well. You test across the pins as you move the arm they it’s range.

 

I changed the tps switch with an autozone product about 6 months ago. Hmmmmmm.......

 

Funny.....i did a tap test on both the tps switch and the Maf
sonsor with the engine under load. Nothing happened....other than it ran flawlessly today....🙄
i ordered a new MAF......315,000 miles. Its time.
plus bucking while accelerating is one of the symptoms.

 

Gotta give rock auto props....2 days MAF to my door!! Nice!
installed.....my runner has not even burped once.
runs like a top... ! $30

 

Hey Sharrack,
I am experiencing similar symptoms. Has the MAF sensor replacement continued to solve your issue?

 

funny i had this issue where when i was wheeling and id floor it to make it up a steep incline id have a quick drop in engine rpm as iff it shut off for a fraction of a second than would scream 4,500k but feel like i had no power. never looked into it much because it only happened 3 times total i believe but always on the same section of back roads near my house up an incline. i later changed out my MAF for an unrelated reason and have never had that issue again and iv been on the trails alot since than.

 

Good to know stout! The MAF is definitely on the hit list of possible replacement items.