Speedometer only works when engine is cold - 1992 Plymouth Acclaim

People on the Jaguar Forums say a poor ground (earth ) connection can cause this symptom. A block of relays control the instrument panel including the speedometer. a corroded or intermittently connected ground. could be it. cold corroded connector would conduct better than a hot one.
https://www.jaguarforums.com/forum/x-type-x400-14/gauges-speedometer-sometimes-dont-work-97892/
Or the relay could be defective.

There are usually TWO speed sensors on modern day vehicles, INPUT and OUTPUT. You may have changed one of these , but you may need to change the other. Ask your parts supplier, they will help you with the other. GOOD LUCK FRIEND.

Very unlikely that it would be a computer problem, it does not control the A/C, or temp gauge. Sounds like multiple problems. A/C could be just low on Freon, if pressure is low, it will not turn on. Temp gauge and rough idle may be related, if temp sensor is bad, the computer wont know the engine temperature and thus not mix the fuel correctly. But there are many things that can cause rough cold engine idle, like dirty throttle plate, or bad idle air control valve. You did not say what engine you have, so this is just general information.

Check for coolant temp sensor fault, It will affect cold start and idle. It controls open loop mode in the ECU (cold, high idle, open loop) Perform an OBDII scan of the stored fault history. Also make sure coolant level is correct.

There is also a cam shaft speed sensor change it and then see. Most other devices require the input of the pulses from this sensor in order to work. Lets face it if the engine (acording to the cam speed sensor) is not running why alow the speedometer to register

renew printed circuit board is the only answer(expensive )

check and replace the speed sensor on the transmission.

if you got no problem restarting your engine then you might better bring it to your dealer to scan the codes for you. Low battery voltage usually is the cause.

does your cruise control work? If not, check the wiring from the VSS to the speedo cluster. Check VSS connector closely for pin pudhout or corrosion

Sometimes, the VSS siganl is converted by the instrument cluster and sent to the PCM and speedo.

Check engine light on?


Speedometer
The electronic speedometer (17255) receives a speed signal from the vehicle speed sensor (VSS) (9E731). This sensor is also used to sense vehicle speed for the engine management system and to regulate the cruise control when equipped.
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Vehicle Speed Sensor The Vehicle Speed Sensor (VSS) (Figure 53) is a variable reluctance or Hall-effect type sensor that generates a waveform with a frequency that is proportional to the speed of the vehicle. If the vehicle is moving at a relatively low velocity, the sensor produces a signal with a low frequency. As the vehicle velocity increases, the sensor generates a signal with a higher frequency. The PCM uses the frequency signal generated by the VSS (and other inputs) to control such parameters as fuel injection, ignition control, transmission/transaxle shift scheduling and torque converter clutch scheduling.

It is either the speed sensor, the wireing in between ot the speedometer module it self. The sensor sends pulse train signal to the speedometer module and there it drives the speedometer and is divided in frequency by about 7 and feed to the computer and the cruise control. When the signal drops the Engine management computer thinks the speed is real slow and raises the transmission pressure.

In the one I had it was a cold solder jooint on the bacjk of the speedometer module itself but this was the divided output and the speedometer itself still worked. The easyest part would be the sensor that mounts on the rear axile I believe and should cost less than 30.00 dollars. If not that thebn it's the wiring or the speedometer module electronics..