Tuesday, 20 March 2012

Idling along

The MR2 has suffered idling problems almost since the day I bought it 10 years ago. It will run along fine for a while until it warms up and then the idle gets erratic after a while, it will over-rev and then conk out at junctions just to embarrass you. Last year I cleaned up and checked over all the plugs and leads and put a new distributor cap and rotor arm on and this improved things a bit, but not much, so this year I'm looking (finally) at the induction side of things.

This is the Air Flow Meter (AFM) on the bench. This is a heavily-made piece of kit compared to the rubbish plastic hot wire ones you get nowadays. It tested out fine and cleaned up nicely. This is the throttle body removed and cleaned up a bit. The throttle position sensor (TPS) is the black thing on the left and the Idle Speed Control Valve (ISCV) is the part on the right. The TPS seems to be okay although it needs adjusting a bit, but when I took the ISCV off, all was revealed (maybe). There are 3 connections on the ISCV, a common B+ (12 volt) and 2 negative connections, one for closing the valve and the other for opening it (seems obvious really). Anyway on application of 12 volts, the opening part is working, but the closing side is sticking. This makes some sense at it means the ECU can't close this valve at all causing bad running and the weird 'feedback' loop at idle as the computer tries to compensate.

I'm going to dismantle this thing tonight and give it a good clean and see if it can be made to work. I hope so because a replacement will be about £200, which is not good.

UPDATE - Toyota have no more ISC valves of this type (worldwide) so I would be looking at around £350 for this little thing shipped from the US!

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