Stutters/jitters at 3500rpm. Won’t rev past 4000rpm under any conditions

[potatofries]

So 1999 4runner limited. Stutters/vibrates jittery around 3500rpm and won’t rev past 4000 even with full throttle in neutral. Having trouble diagnosing problem. Anyone encountered this before?

I’ve already done the following:
New plugs/wires and caps
New MAF
New TPS
New air filter.

Some of these were overdue, but tired of throwing money at parts.

 

[spartacus]

So 1999 4runner limited. Stutters/vibrates jittery around 3500rpm and won’t rev past 4000 even with full throttle in neutral. Having trouble diagnosing problem. Anyone encountered this before?

I’ve already done the following:
New plugs/wires and caps
New MAF
New TPS
New air filter.

Some of these were overdue, but tired of throwing money at parts.

No CEL, Clogged exhaust or catalytic convertor would be my guess specially because it won't rev past 4000 in neutral.

 

[spartacus]

Disconnect the catalytic converter fr9m the headers and see if it makes a difference.

 

[IVD4R]

Disconnect the catalytic converter fr9m the headers and see if it makes a difference.

That should help detect where the problem is

 

[alumarine]

Have you used OBDII reader to check for codes?

 

[phattyduck]

Have you checked mechanical timing (cam/crank alignment)? All you need to do is move the upper rad hose clamp and the upper timing cover to see all the marks needed.

-Charlie

 

[slopp]

Just had this issue. Had the vacuum line off where it plugs into the top of the drivers side valve cover. Near the firewall.

 

[2TH4IST]

Didn't have this issue, but while I was replacing that hose (on drivers valve cover) the steel pipe insert pop out. It was loose in the vc. So cleaned both the pipe and vc and silicone it back into place and tapped it back in. It seems my mpg's went up after doing that.

 

[davidch]

I nursed a friend's '96 Tacoma from Missoula to Seattle back in 2014. Same 3.4 V6 engine, the 5VZ-FE.

It behaved about the same way. The problem turned out to be the fuel pump. It had ingested something, very tiny, when its filtering sock had fallen off. So it could pump enough fuel under enough pressure to generate the HP to hit 60 on level ground, but no more. It was hard to start: I resorted to priming it with a small bit of fuel into the air cleaner connecting tube.

The pump failed atop Snoqualmie pass, finally seized up completely, and popped its fuse. The good side of this story is that the popped fuse made locating the problem much easier.

So, check your fuel pressure.