That chassis was not known for the wire harness problem of the earlier 104s.
But your condition could be unmetered air bewteen the MAF and the intake. There are two comon places to check on a car that has had a gasket job.
The 2 places are :
The clamp where the intake air cross pipe meets the throttle valve assem..they forget to tighten that clamp b/c it is hidden once things go back together..it has to be gotten with an extra long screwdriver , accessed from the front.
The other is they forget to clip the little IAT sensor back into the same pipe.

And lastly, look for any vac leak sources/hose/etc..........

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A Dalton