M20 engine doesn't hold consistent idle, surges in and out... need help

[sbaez10]

Hello to all,

Just swapped out an 87 M20 motor and put in a 89 M20 in and while the 89 M20 was out I resealed the whole engine and put in new high lobe camshaft and had the head resurfaced and other small items. Now the engine is in and won't hold a consistent idle, if left the idle dies and i have to start it up again. Please help need an expert with these motors....

[TimeMachinE30]

Vac leak? Look at the elbow as it is a typical place for leaks.

[zoomer]

If by "High Lobe camshaft" you mean more aggressive camshaft - there lies your issue.
You most certainly need a remap at least, and if the new camshaft is too aggressive you need to raise the idle RPM.