Caterham Roadsport Hot Idle Fix MAP

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And Then - Hot/Surging Idle Problem

Next idling problem - a surging idle when warm, it would rev up to about ~1500 and back down to ~1000 (normal idle) about every couple of seconds. This became highly annoying. I suspected this f***ing MAP sensor again although most research pointed at the throttle position sensor (TPS) or lambda sensor.

The TPS is easy to test, unplug it and measure the resistance across it as you move the throttle, it should be linear and not jump about, go open or any combination thereof. (I am writing this months later so cannot remember what was min and max.) After reading some things saying the lambda sensor can be damaged just measuring voltage on it (some can, apparently) I decided to try that last. So back to the old MAP sensor. I tried unplugging it while the engine was idling and that killed the engine instantly. However this led to the breakthrough - just touching the wires in the right way on it before unplugging it started to cut the it looked like a dicky wiring problem!

Unplugging it I quickly realised trying to clean the pins by poking them with a small flat bladed screwdriver was never going to work - then I remembered I had this tool for popping out the connectors of male plugs. [I have had it since I was little from when I used to do RC car racing and it would pop out Tamiya battery connectors.] I have a picture here of it as have no idea what it is called!

Connector plunger.jpg

Basically its a very thin tube with a plunger in it. Just so happened this just fitted and easily popped out the pins on the MAP plug. Two were slightly corroded, the third quite corroded. I have no idea how as the plug/socket is well sealed. I have a feeling there was a splillage around the battery area at some point so maybe a tiny bit of acidic water got in somehow or maybe just water collects on it easily as the wires enter from the top vertically so any moisture runs down and collects on it?

Anyway metal polish seemed the best way to remove it without damaging what looked like nikel coating of the pins. So lots of elbow grease and sore fingers later, I had three shiny pins and after popping them all back, the Caterham is back to idling normally!


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