Cleaned my throttle body and IACV, now idles high in P and N

DavidA · Post by **DavidA** » 11 May 2013, 15:14

OK, cleaned out both my IAC valve and my throttle body today. It fixed the car shaking at red lights with the AC on, but now every time I have the car in park or neutral the RPM's are sky high. I start it up and it immediately jumps to 2100 RPM, creeps up to 3500 RPM after a few seconds, holds steady for about 10 seconds and drops back down to 2100 and holds steady. As soon as I shift it into drive or reverse, it drops down to about 700 and holds steady at 500 RPM when stopped.

Has anyone ever had this problem? Does the ECM dictate the IAC valve and has to "relearn" the amount of air to give the intake manifold? The CEL is not coming on, so I don't think something has gone bad. I've read that some cars with this issue has the problem go away after some time and others have to have the computer reflashed to get it to behave correctly again.

This is on a 1994 940 sedan, non-turbo.

JohannReinhard · Post by **JohannReinhard** » 12 May 2013, 14:46

Have you had a mechanic look at this idle problem before? Some lazy mechanics will merely crank the idle up to mask the symptoms of a dirty IAC or throttle body. If so, perhaps this is your problem. The high idle can be adjusted back to within specifications by yourself, provided you're comfortable with messing around under the hood.

My Volvo 240/850/940 Pocket Manual says the idle speed for the 940 in park should be 775 RPM, certainly not as high as you're reporting it to be. Were the IAC and throttle body really, really gummed up?

DavidA · Post by **DavidA** » 13 May 2013, 09:53

No mechanics yet, I have only recently bought it. Also, while they were dirty, the weren't horribly gummed up.

I tested the idle adjustment by starting her, shifting her to neutral and clamping down the hose to the IAC valve. It dropped the RPM to about 550. I took the clamp off and tried to adjust it from there, but as soon as I got it down just a little the engine jumped down to 100 and sounded like it wanted to stall.

Is there a way to adjust the IAC valve directly? Could cleaning it have broken it somehow?

DavidA · Post by **DavidA** » 13 May 2013, 10:18

Also, I've established that it idles high at all times, when brakes are applied its only 700 RPM, but let go and it will slowly go up to 3000 when you let off the brakes.

JohannReinhard · Post by **JohannReinhard** » 13 May 2013, 17:37

Okay, it sounds like the problem is isolated to the throttle body, because I can't imagine the IAC valve causing RPMs to climb over 3000. It may even be that when your foot is on the brake and the IAC activates, it retards the airflow as much as possible to bring the RPMs down (the exact opposite of what it's supposed to do: again, a guess only).

If I had to take a guess, it sounds like you did something you shouldn't have when you cleaned the throttle body, most likely knocked the throttle position switch out of alignment or trashed it completely (possible if you sprayed carb cleaner or any other solvent on it). Look here for a little more info and some troubleshooting tips. If you need a new throttle position switch, FCP Euro sells them for $68 new if you have Bosch fuel injection. I don't know where to find one for cars with Regina fuel injection. I should probably locate a source, since I have Regina FI on my 940. You'll need a new gasket if you have to replace it ($3.25).

Hope that helps!

DavidA · Post by **DavidA** » 14 May 2013, 13:21

It did actually. The TPS was fine. I never acutually sprayed in there. I read the write up on how to do it for a 940, and it warned against spraying it on the TPS, so I decided to play it safe and I sprayed TB cleaner on an old microfiber cloth and wiped it out. Worked like a charm.

My problem was with that adjustment screw that the throttle control arm rests on when it shuts. The locknut that secures was missing (I thought I had secured it tightly after adjusting it after cleaning it, but I guess I was wrong) and somehow the vibrations let the screw work its way up. It worked its way up just enough for the arm to rest on it just below the second, highest click. I had fiddled with it for 10 minutes thinking it was right where it should have been under that click, not knowing there was two.

I've got a new gasket in on its way.

JohannReinhard · Post by **JohannReinhard** » 21 May 2013, 05:21

David, any luck solving your high idle issue?