I recently swapped out my 96 stock 1.6 to a 99 1.6 and the rpms are going up and down from 1,000 rpms to 2,000 rpms, any ideas on what could be causing this?

 

IACV, Head Gasket, Computer needs to "learn" new engine or reset itself after being unplugged, air bubbles in the cooling system... way too many to list, try some of these then re-post with results

 

vaccuum leak, iacv

 

Cooling system is good, I have the battery disconnected til morning to see if it will learn the new engine, and Im checking the IACV as we speak, oh and the head gasket is brand new I just put it on, Ill check back in the morning

 

good luck!

 

Idle air control valve malfunction will cause this issue. Its a common and easily fixable problem. Replace the sensor. If that doenst do it, then there may be a vacumm leak, but that would also cause misfire and eratic idle issues, rather than a simple Lope between 1000 and 2000 rpm

 

Is there a CEL? This might help.

 

Yeah it was the IACV thanks for the help guys