91 Lexus ES250 Idle Jumping Problem

[ladoo]

I am a little stumped with this one. I have a Lexus '91 ES250 with about 170K miles and otherwise it runs OK for its age except for about last few weeks.

The idle has been jumping between 1500rpm-2000rpm when either warm or cold more so when warm. Also sometimes it quickly oscillate between the above two rpm's. Other times it idles normally. On many occasions it just stalls as I give gas and would restart but as soon as I put it into drive or reverse it dies again. If I let it run for sometimes then it would get to the high idle again and would go it's merry way.

I have read a lot of material here on this board and thought it would be the ICS valve and took it out and cleaned the plunger part of it and also the hole that it goes into the throttle body just past the butterfly. Because the car works fine sometimes and not others, I could not really make out after I did this. But recently bought a used ICS valve from eBay just to try it out if that is the culprit, but it also acts the same way, so I am now confused if this is the cause or I have gotten another bad one from eBay.

There are no engine codes showing, so that is another thing that is not so obvious.

I would really appreciate it if someone could steer me in the right direction. The notion of purchasing this part new if this is the cause is an expensive one- about $300-$450. So I wanted to make sure if it is this or could it be something else. Due to the age of the vehicle I am wondering if I should spend this amount of money or should just junk it.

Your advice will be very much appreciated. Best regards!