Rear tire traction/spinning

[OClem]

2001 Rodeo
2WD
Automatic
86,000 miles

About a week ago the service engine light came on for a few hours, then went off, then the abs dash light came on for a brief time till I turned off the ignition.

Ever since, so it seems, when starting from a stopped position, like a red light, in first gear the rear tires surge as if trying to peal out. As soon as the gears shift there is no problem. This will happen a couple of times in a row then it seems to settle down until it sits for a few hours, then the problem repeats.

The trouble code did not say anything specific and the service engine light has not come back on.

The mechanic thinks it may be an idle sensor but it is only a guess.

Any ideas?