idle surging at cold start?

[MellowVR4]

hey guys and gals. Im having a little issue with my DD, its a 91 talon awd auto. when i first start the car in the morning the rpm's jump to 2krpm and stays their for like 30 sec then the rpm drop down to 1800 rpm, when that drop happens immeatley the car starts to idle surge and it doesnt stop until the car is running at normal operating temp. Now that the cars warm its idleling fine, but if i mess with the bis screw and turn the idle up back to 1500 rpm its starts idle surging again, but then i turn it back down then it goes away. Does anybody know what can be causing this problem. so faR ive changed the main temp sensor, o2 sensor, maf and isc. need some help troubleshooting this issue im having. So if anybody has had this problem before please let me know what u did to make it go away please, thnx. will be very appreciated.

 

Have you did a boost leak test?

 

[MellowVR4]

lol i wanna do that but i have an exh leak where the manifold meets the turbo, i mean a bunch of air is gonna be coming out of their so ill have to fix that to do a boost leak test. But i will be doing that soon.

 

check boost leaks, can mess with a/f cause surging....

maybe check around throttle body gaskets if they are leaking it will have the same effect

 

[MellowVR4]

ok i will try to do that this weekend

 

[doelcow]

Sounds more like an idle air issue. Your computer has a table based on coolant temp for adjusting idle air. If the BIS is opened up too far the ecu tries to compensate by closing the isc. If it's way out of the range of what the ecu can compensate for it usually surges back and forth wildly until your car warms up and it has less control over the isc. Turn in your BIS a bunch. If you are trying to maintain a 1500rpm idle you may try disconnecting your idle switch.

 

[496of2000]

Did you follow the hints on how to adjust the BISS from vfaq.com , it's listed under the intake section.

 

[shredder2010]

Samething with my galant till she warms up