texasjack Posted June 7, 2017 Share Posted June 7, 2017 My 1990 4.0 runs great when it is cold but when it gets to operating temp it has a rough idle. I put new plugs, wires and number one fuel injector. Checked compression and it is 145PSI. And suggestions would be appreciated. Thank you Texasjack Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 8, 2017 Share Posted June 8, 2017 Check (or replace) the O2 sensor. I think Cruiser has a writeup in the DIY forum on checking the Renix 3-wire sensor. Link to comment Share on other sites More sharing options...
cruiser54 Posted June 9, 2017 Share Posted June 9, 2017 Probably is it. but the ground for the O2 sensor or it's relay can be a contributor. I would perform Tips 1,3,4, and 5 first. Then test the O2 sensor. Should you decide to change it, use only NGK/NTK Link to comment Share on other sites More sharing options...
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