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1999 Ford Escort Engine Won't Start: Fixing P1506, P0171, and P0420 Codes

Model: 99 Ford Escort Fault Code: P0171 Posted: 2008-12-07 10:45

I own a 1999 Ford Escort with a non-original 4-cylinder engine that has recently stopped running. After retrieving the trouble codes using an OBD-II scanner, I found three key error codes: P1506 (Idle Air Control Overspeed Error), P0171 (System Too Lean - Bank 1), and P0420 (Catalyst System Efficiency Below Threshold - Bank 1). I inspected the spark plugs, ignition wires, and vacuum lines. The spark plugs are worn and require replacement, but they were found wet with fuel—indicating that the fuel pump is likely functioning. However, when I tried to start the engine using starting fluid, there was no response from any cylinder. This suggests a problem in the ignition system or related components such as sensors or vacuum lines. My current plan is to begin by replacing the spark plugs and ignition wires, and if necessary, the ignition module. I will also inspect and replace any faulty vacuum hoses, as these can significantly impact engine performance. If the engine still won’t start after these steps, I’ll be unable to proceed with repairs for the other codes. I’m aware that 1990s Ford engines—especially those with split-port designs—are known for complex fuel and ignition systems. I’m seeking advice on where to focus my troubleshooting efforts to get the engine running again.

Related fault codes

P0171P0420P1506

Comments (3)

Anonymous 2008-12-09 21:17

The P1506 and P0171 codes are likely caused by a faulty Mass Air Flow (MAF) sensor. On late-90s Fords, MAF sensors are prone to failure and can send incorrect signals to the Powertrain Control Module (PCM), leading to excessive fuel delivery. This rich mixture may explain why spark plugs are wet with fuel and could also contribute to the P0420 code, as the catalytic converter cannot process high levels of hydrocarbons. A simple test: unplug the MAF sensor. If the engine runs smoother afterward, a bad MAF is almost certainly the issue. While you're at it, clean the airbox and install a new high-quality air filter to improve airflow.

Anonymous 2008-12-11 05:58

A vacuum leak is a likely cause of both P1506 and P0171. The P1506 code indicates that the PCM cannot maintain the proper idle speed, which often points to a faulty Idle Air Control (IAC) valve or an unsealed vacuum line. A lean condition like P0171 can also result from air leaks, as they allow unmetered air into the intake system. While P0420 is typically linked to a failing catalytic converter, it may be secondary to these issues. Since your engine isn’t original, I’d confirm whether this 4-cylinder model was compatible with the Escort platform. Also, if spark plugs are soaked in fuel, check for spark and ensure the timing belt (if present) hasn’t broken or slipped—this could prevent ignition altogether. The listed codes do not typically prevent a vehicle from starting.

Anonymous 2008-12-16 15:56

My friend has a 1999 Escort ZX2 that developed similar symptoms: P1506 and P0171. I initially dismissed it since she could still drive the car and it would restart after stalling—but when she mentioned driving one of my Chargers, I fixed it. The issue turned out to be a deteriorated PVC vacuum hose with two 90-degree elbows—one at the PCV valve and another near the intake plenum. These joints are prone to cracking due to heat exposure. Dealerships sell the full hose for $33, but the elbow fittings are specific: one is 3/8-inch at the PCV valve and another transitions from 1/2-inch to 3/8-inch at the manifold. I fabricated custom elbows using standard pipe fittings until the dealer restocked the complete hose assembly.