Possible Cause & Correction

Check ignition timing.
Check part/neutral switch circuit. See PARK/NEUTRAL SWITCH DIAGNOSIS chart in the TBI TESTS/CODES article in this section.
Check for leaking injector.
Check fuel pressure. See CHART A6 - FUEL SYSTEM PRESSURE TEST chart in the TBI TESTS/CODES article in this section.
Check injector delivery (too rich or too lean)

If rough idle only occurs HOT, check for:

Vacuum leaks: Block idle air passage using Plug (J-3047). If closed throttle engine speed is above 650 RPM, locate and correct vacuum leak (disconnected thermostatic vacuum hose or cruise control hose).
Park/Neutral Switch operation. See PARK/NEUTRAL SWITCH DIAGNOSIS chart in the TBI TESTS/CODES article in this section.
Sticking throttle shaft or binding linkage causing high TPS voltage (open throttle indication). ECM cannot control idle if this condition exists. Monitor TPS voltage (1.2 volts with throttle closed).
Roughness, stoppage, and/or hard starting as a result of EGR flow being allowed during idle. See EGR SYSTEM CHECK chart in the TBI TESTS/CODES article in this section.
Battery cables and ground straps should be clean and secure. Erratic voltage supply will cause IAC valve to change position, causing poor idle quality.
If system voltage is below 9 volts or greater than 17.8 volts, IAC valve will not move.
On 2.5L engines, ECM should compensate for power steering loads. Loss of this signal would be more noticeable under parking conditions where power steering loads are greatest. See POWER STEERING PRESSURE SWITCH TEST chart in the TBI TESTS/CODES article in this section.
MAP sensor. With ignition on and engine off, compare voltage reading of MAP sensor with that of known good vehicle. Voltage readings should be within 400 millivolts of each other.

Start and idle engine. Disconnect sensor connector. If idle improves, substitute a known good MAP sensor, and repeat test while checking the following:

Check A/C compressor, A/C relay, or A/C signal. See A/C CLUTCH CONTROL DIAGNOSIS chart or A/C "ON" SIGNAL DIAGNOSIS chart in the TBI TESTS/CODES article in this section.
A/C refrigerant pressure too high. Check for overcharge or faulty cycling switch.
Check PCV valve for proper operation.
Perform compression check.
Inspect oxygen sensor for silicon contamination from fuel, or use of improper RTV sealant (sensor will have White, powdery coating that will result in high, but false, signal voltage). In return, the ECM will reduce amount of fuel delivered, causing a severe driveability problem.
Check AIR management system for intermittent induction of air to exhaust ports while system is in "Closed Loop".
Monitoring system will help identify the cause of the problem. If the system is running lean, see CODE 44 - LEAN EXHAUST INDICATION flow chart. If the system is running rich, See the CODE 45 - RICH EXHAUST INDICATION flow chart. These tests are in the TBI TESTS/CODES article in this section.