Sudden Erratic/Weird Idle on my AE92. Help me out fellas! -from the Philippines

[TightAE92]

I'm sorta an expat, living in the Philippines temporarily, picked up this AE92 sedan to play with while I'm here. Its bone stock, Philippine market version, 4AF, no emission controls, no O2, etc.


My 4AF is completely stock and up until this problem, it ran perfect. On my way home, normal engine temperature, punched it a little. After shifting into 2nd gear at 5K rpm, the idle wouldn't drop all the way down. It stayed at 2K rpm. Got it home, the idle would'nt drop below 2k rpm and the needle was bouncing up and down. After i let it cool down, the idle was around 1K-1100 but bouncing up and down.
After letting cool down completely for an hour, the idle is now under 1k BUT bouncing. Sometimes, it will drop to about 600 rpm an the engine will die. When i give it gas, it revs fine, no missfire, and power delivery is the same, strong. Its just the idle wont stay steady now. Before this happened, my idle was perfect, right under 1K when warmed up, even when i turn on the a/c, it barely dips down.
I'm thinking a vacuum line somehow got pulled out. Ive had efi cars all my life and this is the first carburated car. I'm hoping someone here can help me out. Luckily, im off from work for a few days and i can spend alot of time messing with it.

hope you guys can point me to the right direction! TIA

-Ray

[Donald]

Look for a vacuum leak somewhere at the intake. Broken or cracked vacuum hose or something loose.

[TightAE92]

thanks for the tip donald. yup, checked all the vacuum lines, didnt find any broken ones, checked all the linkages, everything seemed fine...now the weird part, drove it around the neighborhood for a couple mins and suddenly it went back to normal! could it be a stuck valve or butterfly in the carb?

[90 GP]

My guess is a leaking vac line at the dual diapram throttle positioner. It's on passenger side of carb on the side. It has couple of vac lines attched. It has two speed settings (dual diapram) one is for when you decelerate to keep throttle from closing too fast and another I believe for when a load is put on engine (power steering/headlights). In addition check all the other vac lines for leaks( there are a s****load of em). Also check computer for codes stored but not triggering check engine light. Here's a link on how to do it. With your emmision setup you may not have any equip to trigger a check engine light but can try to see if it would help to narrow down your problem .

http://www.troublecodes.net/Toyota/