What Causes Engine Surge?

Updated on February 6, 2020
Dan Ferrell profile image

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

Engine surge sources can vary from one model to the next.
Engine surge sources can vary from one model to the next. | Source

There can be many causes for engine surge and they may vary from one car model to the next. When this fault appears, there are a number of components or systems you may want to look into first:

  • Vacuum leaks at the intake manifold or vacuum hoses
  • Leaking, sticky or partially restricted fuel injector(s)
  • A faulty emission control system
  • Bad fuel pump
  • Faulty fuel pressure regulator
  • Clogged air filter
  • Restricted PCV system or valve
  • Bowl vent valve stuck open in a carburetor

What Is Engine Surge?

Basically, when an engine surges, you notice your car speeding up and slowing down even while you keep the accelerator steady. You may notice the tachometer fluctuating, for example, from 1500 to 2000 rpm. At the same time, you may feel a soft and rhythmic jerking motion.

The problem may come from a faulty sensor or system that is making the computer deliver too much or too little fuel, and then try to correct the fault by over-compensating.

Watch the next video for an example of this type of problem.

How the Tachometer Reveals Engine Surge

Diagnosing Engine Surge Issues

Finding the cause of an engine surge problem can be time-consuming. However, some strategies can help you get to the root cause of the problem.

  • Pay special attention to systems in need of maintenance, like ignition, fuel, the PCV, and air cleaner systems. Sometimes, a simple maintenance procedure can fix the problem.
  • Also, there are several components in emission systems that may cause an engine to surge when a fault is present. So make sure to download diagnostic trouble codes, even if you don't see the check engine light on.

The following sections help you implement this type of strategy and focus on the most common systems or components related to engine surge issues. This can make your repair easier.

Sometimes, doing due maintenance on an engine system can fix engine surge.
Sometimes, doing due maintenance on an engine system can fix engine surge. | Source
Index
1. Maintaining Engine Systems
2. Searching for Diagnostic Trouble Codes
3. Checking for Vacuum Leaks
4. Idle Speed Control Issues
A Quick IAC or ISC Test
5. Checking Ignition System
6. Check the Fuel Pressure Regulator
7. Restricted PCV valve or system
8. Is This a Transmission Problem?
9. Catalytic Converter Issues
10. Other Potential Problems

1. Maintaining Engine Systems

An engine with a performance issue may not give you a clue where to start with your diagnostic. In this case, pay attention to those systems in need of maintenance.

When was the last time you changed:

  • the spark plugs
  • the spark plug wires
  • the fuel filter
  • the air filter?

When was the last time you checked or cleaned:

  • the PCV valve
  • the EGR valve and gas passages
  • the IAC motor air passages?

In your car owner's manual or repair manual, take a look at the maintenance schedule. Check those items that are up for service. A simple task like replacing an old air filter can stop engine surging.

Many maintenance tasks are simple procedures in many vehicle models. And you can do many of these tasks yourself at home using common tools. Consult your car repair manual.

You can get a relatively inexpensive, aftermarket repair manual from your local auto parts store or Amazon. Haynes manuals come with step-by-step procedures for many troubleshooting, maintenance, and part replacement projects. You'll recoup your small investment in a short time.

Diagnostic trouble codes can point you in the right direction to the source of engine surge.
Diagnostic trouble codes can point you in the right direction to the source of engine surge. | Source

2. Searching for Diagnostic Trouble Codes

Besides your car's maintenance schedule, your car's computer should be your first source of information when trying to diagnose an engine surge problem. The computer monitors many emission controlled systems through actuators and sensors. These components may stop functioning properly and can trigger the check engine light when they begin operating outside their programmed parameters.

For example, a number of sensors or actuators can lead to engine surge when a fault is present:

  • the EGR system (a valve that sticks open or a faulty solenoid or circuit)
  • an oxygen sensor
  • the throttle position sensor (TPS)
  • the mass air flow (MAF) sensor
  • the air charge sensor (ACS)
  • the idle air control (IAC)
  • throttle position sensor (TPS)
  • mass air flow (MAF) sensor
  • manifold about pressure (MAP) sensor
  • vehicle speed sensor (VSS)

A fault in any of these components or systems may trigger the check engine light (CEL).

Often actuators and sensors wear out and begin to run within their maximum or minimum parameters without setting a diagnostic trouble code, even though they are causing a driveability issue. Still, these actuators and sensors may trigger a pending code in the computer memory that can give you a clue about the component or system involved in the fault. So download diagnostic trouble codes, even if the CEL is not on.

And here's a tip: if your engine surges and you find trouble codes P0171 or P0174, be suspicious of a potential vacuum leak. The leak may come from a loose or bad vacuum hose or gasket. Head over to the next section.

A vacuum leak can lead to engine surge.
A vacuum leak can lead to engine surge. | Source

3. Checking for Vacuum Leaks

Vacuum leaks are not uncommon and can lead to many driveability problems, including engine surge. This is true especially on vehicles equipped with a manifold absolute pressure (MAP) or, sometimes, a MAF sensor.

As vacuum hoses age, they may turn brittle, collapse, tear, or fall off their fittings.

When searching for vacuum leaks, check for:

  • proper vacuum hose routing

  • tight connections

  • hose damage, like hardening, cracks, cuts, kinks, tears

  • broken tees

  • vacuum connections and hose condition in components like:

    • EGR valve
    • fuel pressure regulator
    • brake booster
    • purge valve
  • signs of contamination like oil, fuel, and coolant

Also, check for loose air intake boot connections and damaged air intake boots.

The IAC motor is located next to the throttle body.
The IAC motor is located next to the throttle body. | Source

4. Idle Speed Control Issues

On some models, a faulty or fouled idle speed control (ISC) motor [or idle air control (IAC) motor] may cause the engine to surge at idle or at low speeds.

A common problem is carbon buildup. It prevents air to bypass the throttle plate as commanded by the car's computer. Whether the motor has failed or is restricted with carbon residue, most car owners can test the IAC or clean the passages using a simple procedure and a few common tools. If necessary, test the IAC circuit and motor for errors.

Often, a faulty ISC or IAC motor will trigger a diagnostic trouble code (DTC). So make sure to download codes from your computer's memory.

Source
One of many pickup coil configurations (integrated in the assembly) used in vehicles.
One of many pickup coil configurations (integrated in the assembly) used in vehicles. | Source

5. Checking the Ignition System

On some models, problems with some components in the ignition system may cause trouble. For example, a bad pickup coil on some vehicles may lead to engine surge.

In the 1987 Ford Escort and similar models, a common source of engine surge is a faulty IAC motor and carbon buildup plugging up air passages. However, the ignition system may cause the same type of problem.

This system is fitted with a pickup coil inside the distributor. When it goes bad, the engine may begin to surge at idle and at any driving speed.

Consult your vehicle repair manual to help you check the ignition system and walk through the different components during your diagnosis.

Also, replace system components according to the service schedule in your car owner's manual or repair manual. For example:

  • Change spark plugs and wires as needed, even if they look in good condition.
  • Check the distributor cap, rotor, and ignition coil, depending on your particular model.

Look for the fuel pressure regulator in the fuel rail, near the fuel injectors.
Look for the fuel pressure regulator in the fuel rail, near the fuel injectors. | Source

6. Check the Fuel Pressure Regulator

A faulty fuel pressure regulator (FPR) or worn fuel pump can vary the pressure and supply of fuel available to the engine, leading to an engine surge problem.

However, before you start checking system pressure, make sure you've changed the fuel filter according to your vehicle repair manual schedule.

Check the correct fuel pressure for your system—it's listed in your vehicle repair manual—and test system fuel pressure using a fuel pressure gauge. This test will help you locate a potential fault in the FPR, fuel line or fuel pump.

Keep in mind that restricted or faulty fuel injectors may also lead to engine surges.

The following video tells you how a fuel filter in a carburetor can lead to engine surge, and how to replace this type of filter.

PCV valve on a SAAB B201T engine.
PCV valve on a SAAB B201T engine. | Source

7. Restricted PCV Valve or System

A faulty PCV valve or system may show a range of symptoms:

  • engine sludge buildup
  • oil leaks
  • misfire at idle
  • hard-start condition
  • rough idle
  • engine surge

On some models, a faulty PCV valve or system may trigger the CEL. Even if the engine light doesn't come on, you may find a trouble code pointing to an oxygen sensor or MAF sensor. So make sure to check the system as well, if necessary. This other post can help test the PCV valve and related components.

A worn-out clutch may cause symptoms similar to an engine surge.
A worn-out clutch may cause symptoms similar to an engine surge. | Source

8. Is This a Transmission Problem?

Faults in an automatic or manual transmission can also cause a problem similar to an engine surge condition. For example:

In an automatic transmission:

  • A faulty torque converter, or worn clutch in a torque converter, may cycle on and off as it tries to engage.

  • A faulty electronic control module may cause sudden changes in gears.

    Sometimes, a simple test can help you diagnose a bad clutch converter. Do this on a safe road with little or no traffic:

    1. While driving, and at a speed just before the surge usually happens
    2. depress the brake pedal just enough to engage the brake lights
    3. accelerate to cause the engine to surge as usual
    4. if the surge disappears, the problem is likely the torque converter, the internal clutch (if equipped with), or the electronic control module.

In a manual transmission:

  • A worn clutch can cause the transmission to slip and fail to engage properly. Sometimes, a simple test can help you diagnose a slipping clutch:

    1. Park your vehicle in a stretch of road where you have no vehicles or other obstacles in front of you.

    2. Engage the parking brake.

    3. Fully depress the clutch pedal.

    4. Start the engine.

    5. Shift the transmission to third gear.

    6. Increase engine speed to 2000 rpm.

    7. Slowly release the clutch pedal to engage the clutch.

    8. The engine should stall.

      If the engine doesn't stall, the clutch is slipping. Usually, clutch slipping is caused by a worn-out clutch disc, but other problems like binding in the clutch linkage or damaged components can also lead to this condition.

Consult your vehicle repair manual, if necessary.

A restricted catalytic converter can also lead to engine surge.
A restricted catalytic converter can also lead to engine surge. | Source

9. Catalytic Converter Issues

Usually, a plugged or degraded catalytic converter causes engine power loss. But it can also lead to engine hesitation and surge.

There are some tests you can do at home to diagnose a catalytic converter problem using a:

  • vacuum gauge
  • back pressure gauge
  • infrared thermometer
  • rubber mallet

In some cases, coolant leakage can destroy a perfectly working catalytic converter. Make sure to diagnose a bad converter correctly and make repairs as needed. Consult your vehicle repair manual, if necessary.

Check the throttle pedal position sensor, if necessary.
Check the throttle pedal position sensor, if necessary. | Source

10. Other Potential Problems

Often, an engine that is surging can be diagnosed without much trouble with a bit of testing.

Other times, it may be difficult to find the source of the problem, especially if you don't have special tools, time or the technical knowledge to zero in on the issue. You may be dealing with a fault in a system or component not mentioned above.

Here are other sources of engine-surge issues and ideas you may want to test or try:

  • On some models, an intermittent fault in a neutral position sensor can also cause a vehicle to surge. As the sensor intermittently reports to the computer the transmission is in gear and then loses the signal, the engine accelerates and then slows down.
  • If your vehicle has a throttle pedal position sensor, you may want to recalibrate the component or test it. Consult your vehicle repair manual.
  • If your vehicle is using aged gasoline, try replacing it with fresh fuel and add a special additive to clean fuel injectors.
  • Call the customer service at your local dealer. There could be a service bulletin for your particular model that might explain the engine surge you are dealing with. A glitch in the computer system, for example, may be giving you trouble.

Whatever the cause, make sure to find the source of the engine surge as soon as possible. A fault that causes your vehicle to accelerate without your control is a safety issue.

In most cases, you can deal with the problem and, often, make the necessary repairs yourself. As described in this guide, start with the simplest sources of trouble and work your way down the list.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2020 Dan Ferrell

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