Hey Robert,




Dave Stevens was very kind to reply back to me with a link to his latest post regarding this topic:

http://www.brickboard.com/RWD/volvo/1358080/940/960/980/V90/S90/940gle_high_idlehelp_run_ideas_throttle_body_adjustment_tb_tps_switch.html

He explains how to set the throttle body and the special part I mentioned is a tweaking of the linkage.

The idle air valve controls the idle by admitting more air. If the engine is getting too much bypass air from a throttle body being open too far, the engine will idle much too fast and there is nothing the ECU or the idle air valve can do about it. I had this problem with mine, and thought all sorts of things were wrong. A little test you can try to see if this is your problem works like this:
with the key off in the ignition, unplug the mass air flow sensor and disconnect it and the intake hose. Start the engine (which will now run in limp home mode and light the check engine light). With the engine running, carefully put the palm of your hand over the throttle opening the block the airflow. You'll feel the suction. If the idle comes down to something reasonable, you've found your issue. I would suggest checking the operation and adjustment of the idle switch. You'll have to readjust it if you adjust the throttle body. Try this before you spend any more money for a ECU.

Hope this helps.

Jon

Hey Robert,




Sounds like to me you have out of adjustment throttle body and/or a out of adjustment or bad throttle switch. Either of these can cause a high idle speed. I've had the same problem with mine. Often the throttle linkage doesn't permit the throttle to close all the way. This section of the FAQ shows you how to check and set the throttle switch.

http://www.brickboard.com/FAQ/700-900/EngineSensors.htm#ThrottlePositionSwitch

The throttle body itself can be out of adjustment, the FAQ has a section that talks about this:

http://www.brickboard.com/FAQ/700-900/EnginePerformanceSymptoms.htm#PoorIdleTBCleanedNowIdleisTooHigh

I remember for some reason (might be wrong) that the B234 had a slightly different spec for the throttle body adjustment. Dave Stevens has helped me out with mine, so I emailed him to see if its different. He may end up replying to this personally, so either way his advice has been very helpful. I would check the throttle body adjustment and the switch before condemning the ECU. If you want to have another around, ebay sometimes has them. Make sure you get the one with correct number.


Best regards, Jon 'Uncle Olaf'