Error codes 0121 and 1404

[texan23]

I have a 1998 GTP with about 215K miles. It has a rough idle when in drive but not so bad when it is in neutral or park. Occasionally the check engine light comes on, but usually goes away the next time I start the car. I got it scanned for the stored error codes and two were stored - P0121 and P1404. I looked them up and found that these are for the throttle position sensor and the EGR valve. Is the fix as simple as replacing these two parts, or is there some other troubleshooting that needs to be done? I do not want to throw parts at it if I can help it. Also, is replacing either of these something that a moderately mechanical person can do?

Thanks.

[BNaylor]

Welcome to AF.

The DTC doesn't mean the two parts - EGR valve and TPS are bad but it is a good indicator. Both are range/performance error codes.

On the EGR you can remove it and clean the spring loaded pintle. Also, clean any carbon out of the EGR manifold flange from the exhaust to the lower intake manifold. You can check the PCM 5 volt reference signal at the electrical connector.

On the TPS check the 5 volt reference signal from the PCM module at the electrical connector and the output back to the PCM module. It will be a varying DC voltage. .4 volts at idle and 4.0 volts at WOT. Voltage should be linear and progressive with no flat spots as you open the accelerator from closed to WOT.

Both are easy to replace and all you need are simple metric tools or Torx screwdriver with proper sized bit. The TPS is plug and play and self zeroing.