wHAT ARE THE CAUSES AND WHAT SHOULD i CHECK?
sERVICE sOON LIGHT CAME ON BUT WENT bACK oFF.
hELP!

 

Possible causes for Code 30 are: A defective ISC motor, loose connection or defective wiring, TPS misadjusted, ECM not processing signal from ISC properly.Clear code and see if it comes back. You will have to perform output cycling test to verify ISC motor and circuit are OK.

 

https://www.cadillacforum.com/m_21586/tm.htm
can you show me how to perform the sequence of tests to determine if the isc motor is at fault?
Your help is appreciated.

 

This is for the DFI Code 30: To check that the ISC motor retracts and extends when commanded to do so by ECM. Clear codes and exit diagnostics, Re-enter diagnostics and enter the output cycling test- code 96. Visually check to see if ISC motor extends and retracts. If that is OK then check ISC adjustment, the plunger pin should not be touching the throttle lever. ( do you get throttle ratchet??) If that test doesn't retract the ISC then check linkage for free movement, disconnect ISC motor, while output cycling jumper harness pin A and B together, connect test light between pin D and ground. Light/ no light?? Light flashes for three seconds replace ISC motor. No light, check for faulty ECM or check circuit #425 which is Pin D for short to ground. ISC motors are a hard item to find, let me know if you need help there.