Most Likely Culprits:
* Mass Airflow Sensor (MAF) issues: A dirty or faulty MAF sensor provides inaccurate readings to the computer, leading to a lean or rich fuel mixture, resulting in hesitation or bogging. Cleaning the sensor (carefully!) is a good first step. If cleaning doesn't solve it, replacement is likely necessary.
* Throttle Position Sensor (TPS): A faulty TPS sends incorrect signals about throttle position to the computer, causing erratic fuel delivery. This often manifests as hesitation or bogging, particularly at low RPMs. Testing or replacement may be needed.
* Fuel delivery problems:
* Fuel filter: A clogged fuel filter restricts fuel flow. This is a cheap and easy part to replace.
* Fuel pump: A weak or failing fuel pump can't supply enough fuel under pressure, especially when accelerating. This needs testing and likely replacement.
* Fuel pressure regulator: A faulty regulator can cause incorrect fuel pressure, leading to poor performance.
* Ignition System:
* Distributor cap and rotor: Worn or corroded components can cause misfires, leading to poor acceleration. Inspect for cracks, corrosion, and worn contacts.
* Spark plugs and wires: Worn or fouled spark plugs and damaged wires can prevent proper ignition. Inspect and replace if necessary. Worn plugs are very common on higher mileage cars.
* Ignition coil: A weak or failing coil can result in weak sparks, causing misfires.
Less Likely (but still possible) Culprits:
* Vacuum leaks: Leaks in the vacuum system can disrupt fuel and ignition timing. Inspect all vacuum hoses for cracks or disconnections.
* EGR valve: A sticking or malfunctioning EGR valve can affect engine performance, causing hesitation.
* Catalytic converter: A clogged catalytic converter restricts exhaust flow, hindering performance. This is less likely to cause bogging specifically at takeoff, but it will significantly impact overall performance.
* Transmission issues (automatic): Problems with the torque converter or other transmission components could cause hesitation or slipping during acceleration. This is less likely to be the primary cause of bogging *specifically* at takeoff, unless the transmission is severely damaged.
Troubleshooting Steps:
1. Start with the simple and cheap things: Check the fuel filter, inspect the spark plugs and wires, and clean the MAF sensor.
2. Check for vacuum leaks: Use a propane torch (carefully!) near suspected leak areas while the engine is running; a change in idle indicates a leak.
3. Get a diagnostic code scan: Use an OBD-II scanner to check for any stored trouble codes. This can often pinpoint the problem. A 1990 Mustang may not have a full OBD-II system, but it may still have a diagnostic system that can provide codes.
4. If you're not mechanically inclined: Take it to a trusted mechanic specializing in older Mustangs. They will have the experience and tools to properly diagnose and repair the issue.
Remember to be safe when working on your car, and always disconnect the negative battery terminal before performing any electrical work. The exact cause will depend on the specific condition of your vehicle. Systematic checking is key to finding the problem.
