> I have a 87 LS with the 4.3L engine and 200C tranny and it idles ate
> 20-25MPH is that normal?? If not how do I fix it.

1987 Service Manual
Section 6E2-B-5

Rough, Unstable, or incorrect idle, stalling.

Check:

- Ignition timing. See Emission Control INfo label.
- P/N switch circuit. See Chart C-1A
- For injector(s) leaking. Check Fuel Pressure Chart A-7
- IAC - See Chart C-2C
- If a sticking throttle shaft or binding linkage causes a high TPS
voltage (open throttle indication), the ECM will not control idle. Monitor
TPS voltage. "Scan" and / or Voltmeter should read less than 1.2v w/
throttle closed.
- Vacuum leaks can cause higher than normal idle.
- EGR "ON", while idling will cuase roughness, stalling and hard
starting. Chart C-7
- Battery cables and ground straps should be clean and secure. Erratic
voltage will cause IAC to change its position, resulting in poor idle
quality.
- IAC valve will not move, if system voltage is below 9, or greater than
17.8 volts.
- Use "Scan" tool to determine if ECM is receiving A/C request signal.
- MAP Sensor - Ignition "ON", engine stopped. Compare MAP voltage with
known good vehicle. Voltage should be the same +/- 400mv (.4 volts)
or
Start and idle engine. Disconnect sensor electrical connector. If idle
improves, substitute a known good sensor and re-check.
- A/C Refrigerant Pressure too high. Check for overcharge or faulty
pressure switch.
- PCV valve for proper operation by placing finger over inlet hole in
valve end several times. Valve should snap back. If not, replace valve.
- Run a cylinder compression check. See Section 6.
- Inspect O2 sensor for silicon contamination from fuel, or use of
improper RTV sealant. The sensor will have a white powdery coating, and
will result ina high but false signal voltage (rich exh. indication). The
ECM will then reduce the amount of fuel delivered to the engine, causing a
severe drivability problem.