Hello,

I have been chasing down a mysterious issue with RPM's randomly dropping on a 2001 4 wheel drive suburban 1500. Randomly, the RPM's will drop and then return to "normal" This happens both at idle and also when driving. When the drop occurs at idle, it typically drops 2-300 RPM's and sometimes the engine will die (but not always). If the engine does die, it has always restarted immediately with no restart issue. When driving, you can feel the engine "hesitate" briefly before resuming normal operation. When under load, the RPM drop is not as significant. I have been through the entire fuel system, and do not believe that is the issue, but along the way I have replaced the fuel pressure regulator and the fuel filter and tested the fuel pump. Overall we I have good steady fuel pressure. I have also replaced the throttle position sensor, no change after this replacement. More recently, I replaced the intake manifold with a new unit (understanding that these have been known to leak air), and replaced all 4 O2 sensors. After replacing the intake and O2 Sensors, the engine runs smoother but the problem persists. Perhaps the most interesting thing about this is the lack of the CEL light being illuminated, there do not seem to be any codes being thrown.

Any ideas on where to look next? I am thinking this is electrical, or ECU, but with no codes, I am throwing parts at it as you can see above. Any insight is greatly appreciated.

Thanks

Greg

 

I've seen may reports of poor ground issues on older trucks causing weird issues so I would start checking engine and computer grounds. I've never had one of your generation trucks so I can't help you there. Someone here will know more than me on locations.