My 1996 Ranger idles extremely high and then so low it almost stalls for quite a while until the engine warms up. Once warmed up, it seems fine.

Now that the cold weather is here, the high idle has gone to extreme...like 4000 rpm for 5 to 10 seconds. This can't be good as the oil is thick when cold and I don't need to starve the bearings.

I suspect the Idle Air Control Valve, but I've researched this a bit and I don't seem to be having quite the same symptoms as people who've had IACV problems.

There are a few codes, but nothing major. One says the engine is running a bit lean, and another referrs to the Purge Canister Flow is non-existent (and that unit is solidly rusted), but neither seem related to the high/low idle issue.

Any thoughts on the matter?

ps: MY next step is to try cleaning the IACV, although my book says not to use solvents. Not sure what they cost from Ford, but the after-market one lists for $144 here. So if cleaning it helps, then I"d feel better about spending the $144 on this old truck.