2000 Volvo S40
1.9L L4 PFI DOHC 16V

When I drive the car it's fine. But after I stop and put it in park. The sitting idle becomes a problem. The RPM begins to go over 1 and then back down to like 0.5 then back to 1.

It does this several times. Revs up and down. Anyone know what the problem could be? Replaced some bad hose lines, a new battery, spark plugs. But still doing this.

Any ideas?

 

The IAC, idle air control. Search this, you will find good info.

 

Someone told me in another topic it might be a bad MAF sensor.

But after reading up on IAC, I realized I already replaced some bad vacuum lines and it helped it a little bit.

The car runs fine otherwise, you really think I'll have to replace the valve? Cause just looked it up and it's gonna cost like $200.

 

You can take it out and try to clean it with carb cleaner.

 

Ye, I do agree. I also think that You can take it out and try to clean it with carb cleaner Or You can check your fuel pump relay.