88 Supra idle
 

I have an 88 Supra, non-turbo. Bought it 4 months ago. Previous owner replaced engine (approx 25k miles on new engine). Car runs & drives great, but... Lately the idle speed is all over the place. Sometimes when I put the clutch in, it idles at something less than 1000 rpm, which seems normal. Sometimes it idles at about 1500, sometimes 2000. This morning it was at slightly over 2000. I live about 2 miles from work and it may be different when I start it and when I stop. Any suggestions?

check the TSRM for some help.
http://www.cygnusx1.net/supra/library/TSRM/

You will just have to start testing things like the TPS, AFM, ISC valve.

First make sure you don't have any vacuum leaks, and the plugs and wires, cap and rotor are good.

Kinda dumb
 

This may sound stupid, but I thought I had an idling problem when all it was was the floor mat had shifted up ontop of the accelerator. Yes, I felt like an A-hole.

Scruff

Not trying to sound like an arsehole, but unsure how else to phrase it
 

... does it idle high at first for maybe 10 or 15 mins and then go down to a normal idle after it warms up ? Cos it could be the cold-start injector doing its normal job

Completely forgot about my original post here. I eventually traced the problem to the idle speed screw. It was loose and the engine vibration caused it to rotate in or out. I could adjust it to a decent, low idle then drive the car for a few miles and the idle would be back to 2000+. Solved the problem by removing the screw and reinstalling with a stiff spring under the head. The spring tension eliminated the vibration-induced self-adjustment.