Diagnostic Procedure

WARNING: This page is about a different car, the 2005 Mazda MX-5 Miata. However, it is still accessible from the selected car via links, so may be relevant.

NO.8 ENGINE RUNS ROUGH/ROLLING IDLE [BP, BP WITH TC] DIAGNOSTIC PROCEDURE

STEP	INSPECTION		ACTION
1	Verify following: External fuel shut off or accessory (kill switch, alarm etc.) Fuel quality; such as proper octane, contamination, winter/summer blend No air leakage from intake-air system Proper sealing of intake manifold and components attached to intake manifold; such as EGR valve, IAC valve Ignition wiring Electrical connections Fuses Smooth operation of throttle valve Are all items okay?	Yes	Go to the next step.
1		No	Service if necessary and repeat Step 1.
2	Connect WDS or equivalent to DLC-2. Turn ignition switch to ON. Retrieve any DTC. Is "PASSED" displayed?	Yes	No DTC displayed: Go to the next step.
2		No	DTC displayed: Go to appropriate DTC test.
3	Is engine overheating?	Yes	Go to symptom troubleshooting No.17 "NO.17 COOLING SYSTEM CONCERNS-OVERHEATING ".
3	Is engine overheating?	No	Go to the next step.
4	NOTE: Following test is for engine running rough idle with A/C ON concerns. If other symptoms exist, go to the next step. Connect pressure gauge to A/C low and high pressure side lines. Start engine and run it at idle. Turn A/C switch on. Measure low side and high side pressures. Are reading pressures within specification? (See REFRIGERANT PRESSURE CHECK )	Yes	Go to the next step.
4		No	If A/C is always on, go to symptom troubleshooting No.24 "A/C ALWAYS ON OR A/C COMPRESSOR RUNS CONTINUOUSLY TBR BP WITH TC] ". For other symptoms, inspect following: Refrigerant charging amount Condenser fan operation
5	NOTE: Following test is for engine running rough with P/S ON. If other symptoms exist, go to the next step. Start engine and idle it. Turn steering wheel right to left. Does engine run rough while turning steering wheel right to left?	Yes	Inspect PSP switch operation and wiring harness between PSP switch connector and PCM connector terminal 4C.
5		No	Go to the next step.
6	Inspect variable valve timing operation. Is variable valve timing operation okay?	Yes	Go to the next step.
6		No	Repair or replace malfunctioning parts.
7	Visually inspect CKP sensor and teeth of crankshaft pulley. Are CKP sensor and teeth of crankshaft pulley okay?	Yes	Go to the next step.
7		No	Replace malfunctioning parts.
8	Measure gap between CKP sensor and teeth of crankshaft pulley. Specification 0.5-1.5 mm {0.020-0.059 in} Is gap within specification?	Yes	Go to the next step.
8		No	Adjust CKP sensor.
9	Inspect for cracks on high-tension leads. Is there any crack on high-tension leads?	Yes	Repair suspected high-tension lead.
9		No	Go to the next step.
10	Inspect spark plug conditions. Is spark plug wet, covered with carbon or grayish white?	Yes	Spark plug is wet or covered with carbon: Inspect for fuel leakage from fuel injector. Spark plug is grayish white: Inspect for clogged fuel injector.
10		No	Install spark plugs on original cylinders. Go to the next step.
11	Start engine and disconnect IAC valve connector. Does engine speed drop or engine stall?	Yes	Go to the next step.
11		No	Inspect IAC valve and wiring harness.
12	Install fuel pressure gauge between fuel filter and fuel distributor. Start engine and idle it. Measure fuel line pressure while engine idling. Is fuel line pressure correct while engine idling? Fuel line pressure 370-420 kPa {3.7-4.3 kgf/cm2, 53-61 psi}	Yes	Go to the next step.
12		No	Zero or low: Inspect FP circuit Inspect for open FP relief valve Inspect for fuel leakage inside pressure regulator Inspect for clogged main fuel line Inspect pulsation damper High: Inspect pressure regulator for high pressure cause Inspect for clogged fuel return line
13	Visually inspect for fuel leakage at fuel injector O-ring, pulsation damper, and fuel line. Service if necessary. Is fuel line pressure fluctuation within specification after ignition switch is turned off? (See FUEL LINE PRESSURE INSPECTION )	Yes	Go to the next step.
13		No	Inspect pressure regulator diaphragm condition. If condition is okay, inspect fuel injector. If condition is not okay, replace pressure regulator.
14	Connect WDS or equivalent to DLC-2. Start the engine and idle it. Access LONGFT1 PID. Measure LONGFT1 PID at idle. Is PID value between -15% and +15%?	Yes	Go to the next step.
14		No	LONGFT1 PID is out of specification. Less than specification (too rich): Inspect EVAP control system. If system is okay, go to Step 16. Greater than specification (too lean): Inspect for air leakage at intake-air system components. If system is okay, go to the next step.
15	Disconnect vacuum hose between purge solenoid valve and intake manifold from purge solenoid valve side. Plug opening end of vacuum hose. Start engine. Does engine condition improve?	Yes	Inspect if purge solenoid valve is stuck open mechanically. Inspect EVAP control system.
15		No	Go to the next step.
16	Remove and shake PCV valve. Does PCV valve rattle?	Yes	Go to the next step.
16	Remove and shake PCV valve. Does PCV valve rattle?	No	Replace PCV valve.
17	Is there restriction in exhaust system?	Yes	Inspect exhaust system.
17	Is there restriction in exhaust system?	No	Go to the next step.
18	Visually inspect CMP sensor and teeth of camshaft pulley. Are CMP sensor and teeth of camshaft okay?	Yes	Go to the next step.
18		No	Replace malfunctioning parts.
19	Inspect engine condition while tapping EGR valve housing. Does engine condition improve?	Yes	Replace EGR valve.
19		No	Go to the next step.
20	Is engine compression correct?	Yes	Inspect valve timing.
20	Is engine compression correct?	No	Inspect for causes.
21	Verify test results. If okay, return to diagnostic index to service any additional symptoms. If malfunction remains, inspect related Service Bulletins and/or On-line Repair Information and perform repair or diagnosis. If vehicle is repaired, troubleshooting completed. If vehicle is not repaired or additional diagnostic information is not available, replace PCM.