weird idle surge/high idle

[spook302]

So I drove over 250 miles today to all the salvage yards in my area for parts for my 91 gsx. Didnt find half of what i was looking for. Anyways On the trip back I pull it out of gear to stop at a light and its idling a little high. Around 1300-1400 rpms. throughout the trip back it did this. But after I have been in a gear and driving it and put it into nuetral it will surge at 1600 drop a 100 rpms then surge at 1500 then drop 100 and it will do this untill 1200 rpms until it just idles at 1200 constant. A quick rev of the throttle and it starts that whole cycle over again until around 1200 again where it will stay and not surge. Car never had any kind of idle problem. you start it up idles high for a couple seconds drops to its normal 850 900 idle unless its the morning when it idles high for a little as it warms up. All vacuum hoses are goos and hooked up with a clamp everything is plugged in. Throttle cable is not to tight and the throttle closed switch is free to open and close when the throttle is opened and then closed. I have haed ic piping and all new hose clamps from last winter. All hooked up and tight everywhere. I cant see any problems but was wondering if anyone had a problem like this that they resolved. No check engine light either....ever. It does work it let me know my coolant temp sensor was going out about a month ago plus my logger cant pull any codes because there are none.

 

[Jrock11]

Hmm lets see the only time my car ever did this was when I disconnected the battery but it only did this for maybe 100 miles until it stopped. The only other thing I think of is a boost leak....have you done a boost leak test by putting a coupler over your turbo inlet with a compressor over it? You'll be suprised what you find dude

 

[spook302]

well it didnt take me long to remember the biss screw. Went to the car and the rubber plug was missing. the biss shook itself loose today throughout all the driving. the IAC was trying to drop the idle in 500 rpm increments at a time until it would drop to 0 duty cycle and that would be around 1200 on my car with the biss all the way out. im really happy i didnt loose that damn thing. And the biss screw has a leak so I will put a new o ring and rubber cap on the biss monday. im happy this was resolved in an hour.

 

[Jrock11]

Nice dude good thinking I wounldn't have thought of that

 

[kawgomoo]

vac leak