'99 S70 Throttle Issues

[NHVolvoNut]

I recently purchased a '99 S70 NA 5 spd and I am experiencing an issue where the throttle position seems to cause a stutter at very light throttle pressure when under a light load at highway speeds. The best way I can describe iit would be at a steady LIGHT (barely off idle) throttle, it feels like the throttle is acting as a two-position switch, on-off at half-second or so intervals. This causes the car to shudder, Slightly more throttle pressure and I get smooth acceleration. No throttle give a smooth coast. It appears the previous owner has XeMODeX repair/re-flash the ETM, ABS and ECU recently. The vehicle was presented as repaired, but within 50-60 miles I had a CEL and non-functioning cruise control. I discussed the issue with XeMODeX, who were good enough to check the ETM and ECU without charge (hat tip to Joshua and Ninus!!). No issues found. I have a clone DiCE and Vida software and I'm seeing the codes: "532D ECM-532D miL requested by throttle unit; faulty signal" and "900E ECM-900E control module, internal fault; faulty signal". After extensive reading on many sites including this one, it appears to me that the vehicle isn't really exhibiting the typical ETM symptoms; idles fine, no stalling, runs well at all throttle positions other than VERY light throttle at speed.
Anyone have any suggestions? Is there some kind of potentiometer at the accelerator pedal?
Thanks!

[abscate]

The 1999 throttle pedal is indeed a wiper pot , can be tested with an ohmeter for nominal
Function. It rarely fails but we are in the years of new failure modes ! I have a spare off Shagg from a 1999 if needed

[scot850]

I had to replace the throttle peddle for a random pedal action. So they do fail. A junkyard unit fixed the issue.

Neil.