98 4.0 TJ idle jumping while driving

[Karis9]

Hey looking for some help with my 98 4.0 tj. It started to jerk cold from a dead stock to 5-10mph. On top of that now the idle jumps sometimes while driving. I replaced the tps a couple months ago so I don’t think it’s that. It has new plugs and a new IAC. Runs strong when I get on it. It’s when I sit at a constant speed where it will start to jump. Was thinking maybe a fuel pump or maybe it needs a set of wires and a distributor? Any help would be greatly appreciated

 

[Chris]

Hey looking for some help with my 98 4.0 tj. It started to jerk cold from a dead stock to 5-10mph. On top of that now the idle jumps sometimes while driving. I replaced the tps a couple months ago so I don’t think it’s that. It has new plugs and a new IAC. Runs strong when I get on it. It’s when I sit at a constant speed where it will start to jump. Was thinking maybe a fuel pump or maybe it needs a set of wires and a distributor? Any help would be greatly appreciated

Here are a few things you might want to consider:

Fuel System: A failing fuel pump or a clogged fuel filter can cause irregular fuel delivery, which can definitely lead to idle and acceleration issues, especially at low speeds.

Ignition Wires and Distributor: Worn or damaged ignition wires can cause misfires, particularly at lower RPMs. If they're original or have high mileage, it might be worth replacing them along with the distributor cap and rotor.

Vacuum Leaks: Check for any vacuum leaks in the hoses or intake manifold. A leak can cause erratic idle and performance issues. You can use a smoke test to help identify any leaks.

ECM Issues: Sometimes, the engine control unit (ECM) can have issues that cause irregular throttle response. If you have access to a scanner, check for any stored codes even if the check engine light isn't on.

Throttle Body Cleaning: If it hasn't been done in a while, give your throttle body a good cleaning. Build-up can impact performance and idle.

Check the MAP Sensor: Though you haven’t mentioned it, a faulty manifold absolute pressure (MAP) sensor can cause poor idle behavior, particularly if the readings are off.

Since it runs strong when you get on it, it seems more likely to be a low-speed issue rather than a complete fuel or ignition failure. I’d recommend checking these suggestions one at a time to help narrow it down.

Good luck, and let us know how it goes!

 

[Karis9]

Here are a few things you might want to consider:

Fuel System: A failing fuel pump or a clogged fuel filter can cause irregular fuel delivery, which can definitely lead to idle and acceleration issues, especially at low speeds.

Ignition Wires and Distributor: Worn or damaged ignition wires can cause misfires, particularly at lower RPMs. If they're original or have high mileage, it might be worth replacing them along with the distributor cap and rotor.

Vacuum Leaks: Check for any vacuum leaks in the hoses or intake manifold. A leak can cause erratic idle and performance issues. You can use a smoke test to help identify any leaks.

ECM Issues: Sometimes, the engine control unit (ECM) can have issues that cause irregular throttle response. If you have access to a scanner, check for any stored codes even if the check engine light isn't on.

Throttle Body Cleaning: If it hasn't been done in a while, give your throttle body a good cleaning. Build-up can impact performance and idle.

Check the MAP Sensor: Though you haven’t mentioned it, a faulty manifold absolute pressure (MAP) sensor can cause poor idle behavior, particularly if the readings are off.

Since it runs strong when you get on it, it seems more likely to be a low-speed issue rather than a complete fuel or ignition failure. I’d recommend checking these suggestions one at a time to help narrow it down.

Good luck, and let us know how it goes!

I appreciate the detailed response! I will get to work and see what I can find out

 

[tworley]

Here are a few things you might want to consider:

Fuel System: A failing fuel pump or a clogged fuel filter can cause irregular fuel delivery, which can definitely lead to idle and acceleration issues, especially at low speeds.

Ignition Wires and Distributor: Worn or damaged ignition wires can cause misfires, particularly at lower RPMs. If they're original or have high mileage, it might be worth replacing them along with the distributor cap and rotor.

Vacuum Leaks: Check for any vacuum leaks in the hoses or intake manifold. A leak can cause erratic idle and performance issues. You can use a smoke test to help identify any leaks.

ECM Issues: Sometimes, the engine control unit (ECM) can have issues that cause irregular throttle response. If you have access to a scanner, check for any stored codes even if the check engine light isn't on.

Throttle Body Cleaning: If it hasn't been done in a while, give your throttle body a good cleaning. Build-up can impact performance and idle.

Check the MAP Sensor: Though you haven’t mentioned it, a faulty manifold absolute pressure (MAP) sensor can cause poor idle behavior, particularly if the readings are off.

Since it runs strong when you get on it, it seems more likely to be a low-speed issue rather than a complete fuel or ignition failure. I’d recommend checking these suggestions one at a time to help narrow it down.

Good luck, and let us know how it goes!

Thanks, AI!

 

[KennethS]

It started to jerk cold from a dead stock to 5-10mph. On top of that now the idle jumps sometimes while driving. I replaced the tps a couple months ago so I don’t think it’s that.

I would not discount this as a TPS issue.

Why did you replace the TPS a couple of months ago?