Any un metered air into the intake will do exactly that. Monitor throttle position sensor value along with mass air flow sensor reading. The 2 should never cross. If it does there is an indication of un metered air like a vacuum leak or a leaky plenum between the maf and the throttle body. Also check the adjustment of your throttle plate and check for build up of gunk. Clean if necessary. A certain amount of air is expected to bypass, so the throttle stop adjustment should hold throttle open just a hair. The tps closed throttle switch should be closed when throttle is closed.
The engine should run with iac disconnected but only barely. Iac should compensate for all else so make sure iac is operating and receiving signal from the ecu. One way to know if iac is working is when ac compressor kicks on how does the engine react?if there is no change in rpm when ac comes on then iac is probably working. If it falls flat on its ass at idle iac probably is sticking.
1. Check for DTC and service those issues.
2. Check for vacuum leaks and repair if necessary.
3. Clean throttle body and reset ecu.
4. Test mass air flow and throttle position sensor and make repairs or adjustments as necessary. (Tip: search these subjects on youtube)
05 Lotus Elise - rev 400