I have a 2005 volvo s40 1.8. am i correct in thinking the iac is located in the throttlebody cover?

The service and repair manual with diagram will help you to locate and fix the problem on your own and you will get the manual from the given link http://toolsnyou.com/

Doesn't have one , your vehicle has electronic throttle control .
ElectronicThrottleControl (ETC), or Throttle Actuator Control (TAC), is replacing the throttle linkage on more and more late model vehicles. The mechanical linkage or cable between the accelerator pedal and throttlebody has been replaced with a gas pedal position sensor and an electronically-operated throttle.

Electronic Throttle Control

Does not need a IAC valve .

Sounds like a dirty throttlebody plate or your electric accelerater assembly is going bad. Clean plate a retest, if it happens more ofter you should replace the gas pedal assembley and the throttlebody assembly.

P1504 Idle Air Control Circuit Malfunction here are possible causes IAC circuit open
VPWR to IAC solenoid open
IAC circuit short to PWR
IAC circuit short to GND
Damaged IAC valve
Damaged PCM

heres what I would check, This code means that there is a fault in your IAC valve located near the throttlebody.

It is your idle air control (IAC) motor. Its located on the bottom of the throttlebody. All you need to do to change it out is remove the air intake hose from the throttlebody, unplug the connector and remove 3 screws. But the part isn't cheap. I would suggest finding on online because at a local parts store it will be around $250

the air filter is located next to radiator on driverside,first remove the inlet tube from throttlebody and then remove the two bolts holding the top to radiator support,you well need to loosen clamps to remove,then on the side of radiator you will see air filter box, release latches and open cover and remove the filter.

under the intake manifold called etm

where is the iac and the idle air control valve located on a volvo s70 1999

First remove the throttle body. Then locate the Idle Air Control Valve and the 2 TAMPER-PROOF TORX screws that attach it. Soak with WD-40 (or equivalent) and use the correct size TAMPER-PROOF TORX bit on your ratchet and remove the screws (make sure not to drop them--they are NOT magnetic). Mind the large O-ring that seals the IAC to the throttle body; don't damage it because you will need it for the new IAC* (* if you don't buy GM replacement parts). While you have the IAC out, spray the **** out of the throttle body and clean the throttle plate with carb spray, a rag, and a old toothbrush(I'm serious--EVERY GOOD MECHANIC HAS ONE). This will break up the carbon and gunk collected over the years and mileage. Once you have a nice, clean, DRY throttle body (*dry is important because carb spray will expand the O-ring on the IAC and it will split or break the seal--which causes poor idle*) lube the O-ring with some White-Lithium grease (spray some on your finger tip and apply) and firmly press the new IAC into place and reinstall the screws. Reinstall the throttlebody and reconnect the hoses and wires. Crank the vehicle and let idle for at least 10 minutes so that the computer can relearn the new IAC positioning. (this is because the old, faulty IAC was sending poor signal to the computer and the new one must be seen to take orders from the computer)
HOPE THIS DOES THE TRICK, SINCE YOU DID NOT ASK HOW TO DIAGNOSE THE PROBLEM.
Mr. Goodwrench

your IAC valve, idle air control valve is under the black plastic cover on the front right corner on the engine, remove cover undo valve, renew gasket and re install. ade 13 years volvo tech