As long as I have owned my 4Runner (4 1/2 years), it has had an intermittent problem where it suddenly suffers from a significant reduction in power which worsens as the engine speed increases, also, the idle speed drops about 150 RPM. The engine felt as if there was little or no ignition timing advance. The ignition timing was set to specification with the connector jumpered and the light flashing (no trouble codes). If I set the base timing to 25 degrees, the engine would run much better (with no pinging). Since this has been an intermittent problem which would only last for a few minutes or a few hours, it has been difficult to diagnose. Over the years, I have monitored fuel pressure and volume, performed routine maintenance with quality components, and replaced several engine management components as they became available (used) for a reasonable cost (ECM, knock sensor, mass air flow sensor, ignition module and coil - it doesn't hurt to have spares). I even rebuilt the engine with EB parts including an R.V. cam and oversized valves. Recently, the power output dropped and did not return. While investigating, I unplugged the TPS. The idle speed came right back up to normal and the power improved greatly. I have driven the vehicle for several days with the TPS disconnected and it continues to run well and the "Check Engine" light has yet to come on. Plugging the TPS back in brings back the problem. Has anyone else experienced this? I know the TPS is a pretty important input for the ECM, but is it reasonable for a failed sensor to cause the engine to run so poorly when the engine is capable of running fairly well with it completely disconnected? By disconnecting the TPS am I putting the computer into a backup mode and masking some other problem? If so, shouldn't I be able to expect a trouble code?
Thanks,
Isaac
