Saturday, March 5, 2011

1998 Mitsubishi Montero Sport rpm drop problem?

Q- After having my battery replaced (or jumpstarted or disconnected during a service), my engine refuses to idle and sometimes wants to die at a stoplight or RPM gets low for few seconds. What happened and what can I do?
A- Basically, your idle adaptive memory was erased when your battery died (or was disconnected) and you're idle air control (IAC) motor is now starting at a nearly closed position. Over time, carbon/oil build up around the throttle plate can restrict the amount of air that can flow past it... as more carbon builds up, the IAC allows more air to bypass the throttle plate to maintain idle (this IAC position is stored in an adaptive memory). Once the battery is disconnected, this adaptive setting is erased, IAC motor is reset, and now you're engine is chocking for air. To get this back to spec, you'll need to clean out the carbon/oil build up around the throttle plate to allow your engine to breathe again.
To clean the throttle plate and throttle body bore, disconnect your battery to erase any adaptive idle memory that you ECU has attempted to restored. After removing the intake hose from the throttle body, use some throttle body/ carb cleaner spray and spray it onto a shop rag and clean the area around the throttle plate bore, and the throttle plate itself- using the rag to wipe the area clean of any carbon buildup. Wipe everthing dry and wait a few minutes to give the cleaner a chance to completely evaporate. Go ahead and reinstall your rubber intake tube and reconnect your battery. Dont forget to reconnect the MassAirflow Sensor if you disconnected it Allow the engine to run for a few minutes and to recheck your idle quality. To verify everything is okay, allow the engine to idle for a few seconds and try grounding the power steering pressure switch wire (there's a single wire going to a switch at the power steering pump). Your idle speed should "bump up" a few hunded RPM's before settling down. You can also try allowing it to idle, then turn on your AC- again, the idle speed should bump up a few hunder RPM's before settling down. Good luck!