87' s-15 loping

[sflichel]

Hi all, havent posted here in awhile. but I have a 87' S-15 2.8L 4X4 standard. When coming to a stop at an intersection the idle really starts "loping"?? What I mean by that is revs up, then down, up then down, then finally settles. I have changed plugs, cap and rotor (plus a new ignition module that went when pulling another truck 300km on a 35C day). I have also replaced both injectors and fuel regulator. I have tested TPS with an anologue metre and it showed smooth movement. Scan tool shows O2 sensor to be rich/lean back and forth. I'm at a loss here, what can I try??? Intake manifold gasket maybe??? (vacuum test shows normal) By the way, it is a recent motor, maybe 10K on it. After driving 4k's oil still looks as clean as it did out of the bottle. Thanks for any help

 

edit: I also removed the idle control motor and cleaned it. is there a way to test these units???

[denton_12]

Check your fuel pressure, my 88 Sierra was doing this, and although it took a while, my fuel pump eventually went out, after replacing the pump, it no longer loped.