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Idle Air Control Valve (IAC) Cleaning DIY

Need to clean your Idle Air Control Valve?

It got warm here a couple of days ago for the first time this year (~80-85F) and our ’97 855 GLT Volvo at 155k miles suddenly started to have a wandering idle speed and stalling at idle, but only when the car was fully warmed up.

The stalling symptom was worst right after restarting the car after it had been running for a while (hot start). I first tried disconnecting the MAF but this did not change the wandering idle and stalling. So, I read up on stalling and rough idle on MVS, found a good post by Ozark Lee and so decided to remove the IAC and give it a good cleaning. Since there wasn’t already a good illustrated write-up, I took some photos along the way:

Step 1

Remove the throttle cover. This requires a T25 screwdriver to loosen the screw on top. When you remove it, the IAC is visible underneath. IAC valve under the throttle cover

IAC valve under the throttle cover

Step 2

Disconnect clamp. I used a sharp flat blade screwdriver to pry off the Oetiker clamp holding the IAC hose to the vacuum nipple (I removed the other two Oetiker clamps on the IAC later, after pulling it out of the car). Then I pulled the IAC hose off of the vacuum tree. Screwdriver prying the Oetiker clamp loose from the IAC-Vacuum tree hose.

Step 3

Disconnect the electrical connector on the back of the IAC. Loosen hose clamps at throttle and intercooler and pull hoses and IAC from throttle. There is a black rubber collar around the IAC valve that has two ears underneath that can be squeezed together to release the IAC valve from support bracket. IAC and hoses after disconnecting electrical connector and hose from throttle.

Step 4

Remove the Oetiker clamps at the IAC connectors. Inspect and clean internal plate. My IAC valve was original (dated ’96) and had never been cleaned as far as I know. There was a lot of yellow and black varnish on the plate that needed to be cleaned off. I used MAF cleaner (hexane) which was not very effective at dissolving the varnish. I used cotton swabs and a flat screwdriver blade to wipe and scrape the varnish off and used the MAF cleaner to flush away loosened deposits. I think the varnish had built up to the point that it caused the IAC valve to stick or respond slowly, making the idle wander and the car likely to stall. If you twist the IAC in your hand the plate should rotate freely. IAC valve with ~15 years build up of varnish (pre-cleaning)

After cleaning, twist the IAC to make sure the internal plate rotates smoothly without sticking or binding. During reinstallation I used new hose clamps to replace the three Oetiker clamps I removed. While I had the intake hose removed from the throttle, I took the opportunity to clean the throttle plate. After putting the IAC and hoses back together, the car is running well again. IAC valve after cleaning. This worked great for me and was a lot cheaper than buying a new IAC (~$200). If I had to do it again, I would probably have bought some more powerful solvent like throttle body cleaner to make cleaning out the varnish a little faster and easier.

IAC valve after cleaning.

Cleaning DIY: 850 IAC (Idle Air control valve) cleaning

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1 Comment

My Volvo 850, 1994 I think the IAC is bad,my car started good but in down ,start up and down and turn off ,and run perfect but in I am Stop in a light in the traffic the car shuts off . What do you think is?

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