96 5VZ 4Runner fails SMOG test

High NO would be casued by an inoperative EGR system.

High NO implies higher than normal combustion temperatures. A lean mixture can cause that. A faulty thermostat or a malfunctioning cooling system can raise temperatures too. Is the temperature gauge reading high? A faulty EGR system, which cools engine temperatures by inserting recycled exhaust gas into the cylinder, can also cause combustion temperatures to get high. In exteme cases, noticeable pinging can be heard. Good luck. Al

Thanks for the Replies!

The EGR was replaced before the test and engine temp is normal. Unless the new EGR is bad or the vacuum lines are leaking clogged, I don't know what else to think of. Also the engine runs normal, no unusual pinging or miss fires at idle. We're gonna try to clean the intake and throttle body, it did seem a bit dirty, and replace the air filter.

Like others said, check your EGR system. Also too advanced engine timing or lean mixture can do it too. Check things that raise combustion temperature.

Check following:

When the EGR system fails it is often not the EGR valve. The EGR system must be checked. That includes the vacuum lines but most importantly the passageways that carry the exhaust gas. Given the corrosive nature of exhaust gas, problems with components that it routinely contacts are not unusual. Good luck. Al

To start with, wasn't the 94 4runner a 3VZ 3.0 liter not a 5VZ? If so, I have seen the EGR modulator (Toyota pt # 25870-65010) get a pinhole leak in the diaphram. The modulator is located right above the power steering pump and is mounted in a clip on the intake plenum. You should be able to rev the engine and see if the stem to the valve on the EGR valve is moving when you increase the engine RPMs, if it is not, you either have a stuck EGR valve or a vacuum leak leading to it.

It's a 96, I'm familiar with what your describing, I have a 93 with a 3VZ. My friend is supposed to get it retested this week.