Part-throttle stumble

[Doug914]

Hello everybody.

My freshly rebuilt 2.1 (a 2.0 with 96-mm p&s's and stock FI) has about 800 break-in miles so far and runs pretty well...with the exception of a stumble that's noticeable as you pick up the throttle from cruise. I had the mixture set by a mechanic, and the plugs look good, with light tan deposits on the electrodes and just a little soot on the "ring" part of the plug.

It didn't have the stumble about 400 miles ago. I'm wondering, since it probably needs a valve adjust about now, if excessive lash here could cause the stumble. All the vacuum connections seem to be airtight.

Also, if I don't give it, say, 2000 revs off the line, the engine loads up and nearly dies. I've richened the idle via the pot on the ECU just enough to eliminate the surge. It's a minor inconvenience, and driven appropriately it's not a problem, but it does tend to catch me out at the most embarrassing times!

Many thanks in advance for any insight.