Toyota 4Runner 1996-2002: Performance Diagnostic Guide

There are a few components that could fail and affect your Toyota 4Runner's performance. Read on to learn how to diagnose it.

By Bassem Girgis - February 12, 2016

This article applies to the Toyota 4Runner (1996-2002).

After driving your Toyota 4Runner for a while, you know when something is wrong with it, especially when it's affecting its performance. The Toyota 4Runner is a strong vehicle, just as long as it runs at its full potential. If your car is not accelerating as quick as it used to, or if it feels like something is holding it back, don't just keep driving, instead, diagnosing it could be quick and simple. If you're ready to make your 4Runner a beast again, then read on to learn how to diagnose its performance issues.

Toyota 4Runner Performance Diagnostic Guide

Materials Needed

  • Socket set
  • Long screwdriver
  • Smoke machine

Step 1 – Check spark plugs and wires

They could be worn or burnt.

The spark plugs are what give your 4Runner spark; the less spark you get, the less performance you will get. The spark plugs should be replaced every 30,000 miles. Inspect your spark plug wires to make sure they are in a good condition. Follow them from one end to the other. If you have any cracks or wears in the wires, they could affect your engine performance. Next, remove each spark plug and check its tip. If it appears burnt, then it is time for a new set of spark plugs.

toyota 4runner spark plug engine problem
Figure 1. Spark plugs, bad vs. good.

If the spark plugs and their wires are in good shape, proceed to Step 2.

Step 2 – Check fuel filter

It could be clogged.

The fuel filter is the gate between your fuel tank and the engine. It's designed to filter the gas going to the engine, and as it gets clogged, the amount of fuel going to the engine decreases. The more clogged the fuel filter, the more hesitant the car will be when you step on the gas pedal. At some point, it could get too clogged that your car won't start. The fuel filter is located under the driver's door, along the frame rail. Disconnect the battery, then remove it. Make sure you don't put your mouth directly on it, so after you cover it with something, blow through it. If you can't blow through it, that means it's clogged.

toyota 4runner engine problem fuel filter
Figure 2. Fuel filter.

If the fuel filter is clear, proceed to Step 3.

(Related Article: How to Replace Fuel Filter -

Step 3 – Clean fuel injectors

They could be dirty.

The fuel injectors are what spray the fuel inside the engine. If they get dirty or clogged, they could spray less gas, which causes the car to hesitate and decrease in performance. Remove each fuel injector and clean it thoroughly. If you see any dirt or grime on the tip of it, clean it really well before putting it back in. You can also check if they are faulty by placing a long screwdriver on each injector as the car is running, then place your ear on the other end and listen. If you hear a buzzing sound, that means it's working properly; if you hear no sound, that means it's time for new injectors.

toyota 4runner engine problem clogged fuel injector
Figure 3. Fuel injectors.

If your fuel injectors are clean, proceed to Step 4.

Step 4 – Check for vacuum leaks

You could have worn hoses.

A vacuum leak is usually accompanied by a mild hissing sound, especially when you accelerate. Visually inspect the vacuum hoses for any signs of wears or cracks. If you have worn hoses, replace them. There is another way to check for a vacuum leak; however, it requires a smoke machine. Pull the brake booster's vacuum hose off, then blow smoke in it, and if you see smoke coming out of one of the hoses, you've found your vacuum leak.

toyota 4runner engine problem vacuum leak
Figure 4. Check for vacuum leaks.

Related Discussions