Pontiac Fiero 1988 Service Manual page 646

DRIVEABILITY AND EMISSIONS - FUEL INJECTION (PORT) 6E3-B-7
ROUGH, UNSTABLE, OR INCORRECT IDLE, STALLING
Definition. The engine runs unevenly at idle. If bad enough, the car may
shake. Also, the idle may vary in rpm (called "hunting"). Either condition may
be bad enough to cause stalling. Engine idles at incorrect speed.
• Perform careful visual check as described at
start of Section "B".
• CHECK:
Throttle linkage for sticking or binding.
Ignition timing. See Emission Control
Information label.
Idle air control (IAC) system. IAC valve will
not move if system voltage is below 9 or
greater than 17.8 volts. See Code 35 facing
page.
Generator output voltage. Repair if less
than 9 or more than 16 volts.
- P/N switch circuit. See CHART C-1A, or use
"Scan"
Tool.
- Injector balance. See CHART C-2A.
PCV valve for proper operation by placing
finger over inlet hole in valve end several
times. Valve should snap back. If not,
replace valve.
Evaporative Emission Control System.
Section "C3".
Power Steering Pressure switch input. See
CHART C-1E or use "Scan" tool.
Battery cables and ground straps should be
clean and secure. Erratic voltage will cause
IAC to change its position resulting in poor
idle quality.
For vacuum leaks.
Manifold absolute pressure (MAP) Sensor -
Ignition on engine stopped. Compare MAP
voltage with known good vehicle. Voltage
should be the same ± 400 mV (.4 volts),
or
Start and idle engine. Disconnect sensor
electrical connector. If idle improves,
substitute a known good sensor and recheck.
A/C Refrigerant Pressure too high. Check for
overcharge or faulty cycling switch. See
CHART C-10.
Exhaust gas recirculation (EGR) valve: There
should be no EGR at idle.
For fuel in pressure regulator hose. If present
replace regulator assembly.
Ignition system; wires, plugs, rotor, etc.
• Run a cylinder compression check. See Section "6".
• Inspect Oxygen sensor for silicon
contamination from fuel, or use of improper room
temperature vulcanizing (RTV) sealant. The
sensor will have a white, powdery coating, and will
result in a high but false signal voltage (rich
exhaust indication). The electronic control module
(ECM) will then reduce the amount of fuel
delivered to the engine, causing a severe
driveability problem.
EXCESSIVE EXHAUST EMISSIONS OR ODORS
Definition: Vehicle fails an emission test. Vehicle has excessive "rotten egg" smell.
Excessive odors do not necessarily indicate excessive emissions.
• Perform "Diagnostic Circuit Check."
• IF TEST SHOWS EXCESSIVE CO AND HC,
(or also has excessive odors):
• Check items which cause car to run RICH. •
• Make sure engine is at normal
operating temperature.
• CHECK:
- Fuel pressure. See CHART A-7.
Incorrect timing. See vehicle emission
control information label.
- Canister for fuel loading. See CHART C-3.
- Injector balance. See CHART C-2A.
PCV valve for being plugged, stuck, or
blocked PCV hose, or fuel in the crankcase.
Spark plugs, plug wires, and ignition
components. See Section "6D".
Check for lead contamination of catalytic •
converter (look for removal of fuel filler
neck restrictor).
Check for properly installed fuel cap.
• If the system is running rich, (block learn less
than 118), refer to "Diagnostic Aids" on facing
page of Code 45.
IF TEST SHOWS EXCESSIVE NOx:
• Check items which cause car to run LEAN, or
to run too hot.
- EGR valve for not opening. See CHART C-
7.
Vacuum leaks.
Coolant system and coolant fan for proper
operation. See CHART C-12.
Remove carbon with top engine cleaner.
Follow instructions on can.
Check ignition timing for excessive base
advance. See emission control information
label.
If the system is running lean, (block learn greater
than 138), refer to "Diagnostic Aids" on facing
page
of Code 44.