Common issues that can occur in vehicles using a throttle body injection (TBI) system include idle surge and stumble. This kind of fuel injection system uses a single injector housed in the throttle body to provide fuel to the engine.
Rough idle, stalling and subpar performance might result from the idle surge and stumble issues. A 350 TBI idles up and down at random is one of the most common. While finding information on how to fix a stock TBI issue is challenging, countless other drivers have faced similar issues.
In our guide, we have compiled all there is regarding a 350 TBI surging idle. So, by the end, you’ll have a better understanding of how to fix your own issues and where to locate various components that you need to access. (Read High Idle After Cleaning Throttle Body)
What Causes TBI Idle Surge and Stumble?
There are a number of potential reasons why TBI systems experience idle surges and stumble. Among the most typical are:
Vacuum Leaks:
The intake manifold system is susceptible to vacuum leaks, which can make the engine run low. As the engine tries to compensate for the low fuel, this might cause idle surge and stumble.
Dirty Throttle Body:
An unreliable throttle body might cause the engine to stumble and surge during idle. Dirt and grime can accumulate over time on the throttle body, reducing airflow and changing the fuel mixture.
Faulty Throttle Position Sensor (TPS):
The engine control module (ECM) receives information about the throttle position from the TPS sensor. The ECM may misunderstand the throttle position if the TPS is broken, which can result in idle surge and stumble.
Faulty Idle Air Control (IAC) Valve:
The IAC valve is in charge of regulating how much air enters the engine at idle. If the IAC valve is broken, the engine may idle badly, which might produce a surge and stumble.
Fuel System Issues:
The fuel system is essential for the engine to run properly in a car with TBI. The engine may operate badly, resulting in an idle surge and stumble, if there are issues with the fuel pump, fuel filter, or fuel pressure regulator.
Solutions for TBI Idle Surge and Stumble
There are various actions you can take to attempt and fix the problem if your TBI-equipped car exhibits idle surge and stumble.
Here are a few potential answers:
1. Check Vacuum Lines for Leaks:
A vacuum leak in the intake system is one of the most frequent causes of idle surge and stumble. Measure the vacuum level in the intake system with a vacuum gauge to check for vacuum leaks. A vacuum leak may be indicated if the vacuum level is low. You must identify the leak’s origin and fix or replace the damaged component in order to stop a vacuum leak. (Read Are Mud Flaps Necessary)
2. Clean the Throttle Body:
The engine may operate badly, leading the idle to surge and stumble if the throttle body is unclean. Remove the throttle body from the car and clean it with a throttle body cleaner to get rid of any dirt or grime. Ensure you use the cleaner according to the manufacturer’s directions. To make sure there are no leaks, replace the throttle body gasket.
3. Replace the Throttle Position Sensor:
A defective TPS might result in the ECM leading the throttle position, which can cause an idle surge and stumble. Measure the sensor’s resistance with a multimeter to test the TPS. The TPS needs to be replaced if the resistance is outside the range specified by the manufacturer.
4. Replace the Idle Air Control Valve:
The engine may idle badly, leading to surge and stumble, if the IAC valve is broken. Using a multimeter, measure the IAC valve’s resistance to perform an IAC valve test. The IAC valve needs to be replaced if the resistance is outside the range recommended by the manufacturer.
5. Check Fuel Pressure:
The engine may operate badly, leading to an idle surge and stumble, if there are issues with the fuel pump, fuel filter, or fuel pressure regulator.
Test the fuel pressure at the fuel rail using an inline fuel pressure gauge to check the fuel system. There can be a problem with the fuel pump, fuel filter, or fuel pressure regulator if the pressure is outside the range recommended by the manufacturer. It will be required to inspect and, if necessary, replace these parts to get the correct injector spray pattern.
Driver 1# Fix for Significant Stumble
When replacing with new plugs, wires, cap, and rotor on a 1991 Chevy, you will find it no longer running poorly, but it can continue to surge at idle.
It basically almost shuts off, surges back to life, and then repeats continuously until you apply some throttle. The surge is probably a little higher than normal idle. It could be that the throttle body or possibly injecters are dirty.
What is the best way to clean them?
You could find the symptoms persist by adding a new idle air control valve and O2 sensor. The engine could still have absolutely zero power at all and an erratic idle, so when you accelerate, it stutters as if it’s missing a few cylinders.
You’ll need to check all cables are secure and tight on the plugs and confirm that they are directing to the right cylinders. In case a vacuum leak is the source of your issues, install a new gasket on the base of the throttle body.
It may need the help of a propane torch to determine if there are leaks in some areas. After doing all this, you’ll need to check your progress tonight and check the fuel pump isn’t on the brink of failure. (Read Cleaning Battery Terminals Without Disconnecting)
If this isn’t the issue, then check the trouble codes before you keep adding parts that won’t fix any problems on cars or TBI trucks. If you are lucky, you could find it ran poorly before it idled smoothly by following the above.
However, if the issue isn’t fixed, you may find it runs well at a very light throttle and when wide open, although you could feel a significant stumble in mid-throttle range. Running your vehicle around, you can find it may barely run after a while, and you again face an erratic idle, although now the check engine light may illuminate on your dash to either side of your steering column.
You may need a timing light or scan tool at this stage, as there is little else you can change to fix the issue. Adding a new cap and rotor here can ensure you have a good pass of power and will prevent any arcs.
Driver 2# Fix for EGR Controller and Sensors
if you have something like a ’44’, you can find that your oxygen sensor voltage can drop to under 0.2 volts in a minute of closed-loop operation. When the O2 voltage is this low, you will be running lean, and thus the oxygen sensor could have been fitted or replaced incorrectly.
The code doesn’t highlight an issue with the coolant sensor but rather that you have an engine issue. It doesn’t hurt to add in a new coolant temp sensor. There could be a vacuum leak, or the throttle body has been cleaned with a carb cleaner.
A new IAC motor is useless when the ports are clogged, and air cannot reach the pintle. If this is the case, you’ll need to check the fuel pressure and possibly replace it with a new fuel filter.
If you have surging idle, lack of power at speed, and low voltage on your O2, then chances are you have a vacuum leak. One thing to note is a MAP sensor can lead you to the same symptoms or cause the same problem as a vacuum leak.
While it may be less common, the MAP will determine the amount of air coming in, thus how much fuel to inject, and can stop it from working properly as a result. These engines run with low fuel pressure but have drivability issues. So, you’ll need to check EGR, disconnect the vacuum line, and plug it in. You may have the same problem but cannot figure out why it stumbles under load.
The EGR operates normally at idle, although your EGR can turn sticky and won’t run smoothly. Replace it with a new EGR, and you’ll probably find it runs fine.
You may need to test fuel pressure, or you have an issue with your map sensor, or the vacuum lines have some blockage. While running, remember the temp sender unit doesn’t affect how your truck runs; instead, it is the engine temp sensor on the intake that is used to make any adjustments.
If you see the check engine light at any time here, it can mean you have a sticky EGR valve, or you have a blockage. Any extremely light part-throttle application while moving or in neutral would cause a series of jerks or surges as if you were deliberately tapping the throttle in a constant drum beat.
It would vanish if you pushed the throttle a little further. A fuel injector cleaner can help with these symptoms, but it can take some time and requires two tanks of fuel with the additive to clear blocked injectors.
A code 32 or equivalent would have been thrown if the EGR had gotten stuck. A tiny vacuum leak can also bring on the same issues at the EGR base gasket. To solve the last remaining component of your problem, replace the gasket. (Read Does The Brake Pad Wear Indicator Go On The Inside Or Outside)
Under normal acceleration, the leak might be negligible enough to prevent any stumbles or surges, but it becomes evident when using power braking or extremely light throttle.
Even while your car will operate wonderfully once the leak is fixed and the injectors are clean, partially clogged injectors, and a minor vacuum leak can still cause a number of vexing issues.
It appears to be a fuel supply issue. Remove your air cleaner and check the spray pattern coming from your injectors. Install an inline fuel pressure gauge and check the pressure if you don’t observe an issue there. Based on previous run ability issues, the in-tank fuel pump has frequently been the culprit.
