I just bought a 92 trooper that was sold because it didn't pass the emissions test. Sure enough when I tried it passed in every way except for idle hc (1350 reading, 750 acceptable). 2500rpm hc was 40, co was .03% at idle and .00% at 2500.


The truck makes a clanking noise that comes and goes from the left valve cover. When I come to pushin the clutch and stop the engine surges a few times between 1000 and 1400rpm then revs to 2000 for a couple seconds then back toidle. I could guess the clanking is a bad lifter or broken valve spring but that doesn't explain the surging.


Any help is greaty appriciated.

 

Looks like the clanking is from a bad lifter. I think the surge is from a bad idle air control valve. I think it is sticking open sometimes. I heard if the throttle is closed the computer shuts off fuel before reaching 1800rpm and will surge until the throttle is opened.