I did a load of maintenance on the wifemobile about three months ago - new front seals, timing belt and tensioner, belts, radiator, hoses, water pump, etc. Car ran great. About two weeks ago the idle shot up to about 1600 and stayed there. I cleaned the throttle body and there was no change. I tried adjusting the knurled idle adjustment screw and it had no effect - except to increase idle when it was screwed waaaaaay out. I also completely disassembled the knurled nut/housing and cleaned it out. (Yes - I realize I probably hosed the adjustment - I'll worry about that later) I checked the adjustment of the TPS per the FAQ and it seems fine. Put it all back together and still a solid 1600 idle. I did notice that when you give it gas and let off, the idle starts to drop below 1600 - maybe down to about 1000, and almost seems like it catches itself and bounces back up to 1600. I figured the extra air had to be coming from somewhere and I couldn't find any vacuum leaks so I partially clamped off the hose from the main air intake pipe to the idle air control valve. Now it idles great. My question is: have I just determined that the idle air valve is bad, or is there something else driving it that may be the problem. What's my next step.

And while I'm posting, I have a stock Volvo AM/FM/Cassette deck with speakers in the dash and the rear doors. I have cutouts and wiring for speakers in the front doors, but I get no sound when I plug speakers into these wires. What gives?

As always, thanks for your help.

The ECU is fried. Confirm this with your multimeter and disgnostic procedues in Bently's Repair Manual.

The procedures call for hooking the meter between the ECU and its multi-pin connector, then testing three or four cirtuits related to the fuel system, including one for the IAC valve.

It sounds like your IAC valve is not working at all and the vanes inside are stuck in the open position letting air thru it. This explains why you have no change in idle when you disconnect the power. If it was a working IAC the idle should have changed noticably.

What happens when you unplug the IAC? Have you taken it off the car yet? If it were my car, I would verify that the default position is closed (only a tiny crack visable in the valve) and bench test it by applying 12 volts to IAC terminals.

--
Matt L. -- Cary, NC -- '89 740 sedan -- '91 740 wagon

Matt, I have unplugged it several times with no effect on the idle speed. That was part of what made me suspect it in the first place. I have not pulled it yet as the damn car keeps disappearing whenever my wife goes out! Anyone know which terminals to apply 12 v to test IAC? I believe there are more than two choices.

Dave,
Had this exact problem on my car ('85 744Ti) just last week. Idle speed went up while driving on the highway, felt a little like cruise control kicking in.

It wouldn't hurt to remove the IAC valve and clean it, but the following can be done while on the car also to diagnose it first.


Checking the connector:
Remove the harness connector of the IAC valve by pressing the wire lock and sliding away from valve.
The centre terminal of the connector (on the harness, not the valve) should always show 12V with ignition on. The other two on either side are grounds that are controlled by the ECU. i.e. activating ground on one side would open or close the valve, the opposite terminal doing the opposite.

With ignition on, check with a multimeter using the red probe on the centre terminal and checking voltage on each outside terminal with your black probe. You will likely notice a variable of 12V through each circuit, one side possibly may be a higher voltage than the other. This is correct for normal operation from the ECU.

How the IAC Valve works:
The IAC Valve is a essentially a magnet where the side (or terminal) with greater voltage will win control of the valve toward that side. It is possible that the valve be in-between the open and closed setting (read half-open or half-closed) with essentially equal voltages to each side.

Check IAC valve for function. Get 2 long wires (long enough to reach from battery to IAC valve terminals) and connect/attach one end of each wire to each of the battery terminals (not one wire connected to both battery posts!).
As you connect the wire from the positive terminal (of battery) to centre terminal of valve, connect negative terminal to either one of the two other terminals on the valve. Switch the negative wire back and forth, between each of the outside terminals. As you do this, you will hear the valve clicking open, then closed, then open, and so on.
This indicates the valve can function correctly and the problem is elsewhere. If this doesn't work, try dis-assembling and cleaning as the IAC valve is not functioning properly. Test it again before installing to see if it now works.

Hint: Check the actual connector from the harness. I spent 4 days trying to diagnose this same problem while the solution was very simple. One of the outside metal terminals inside the connector was loose and was being pushed back further into the connector causing it not to make contact, and therefore the valve staying on open setting all the time. Solution was to pull the metal terminal out, bend the locking tab and re-inserting into plastic connector. Problem solved, hope yours is this easy too!

Cheers,

Andre Corriveau
'85 744Ti - current
'83 244Ti, '89 744Ti, '94 855Ti
Can you tell I like Turbos?
Ontario, Canada

Dave, just crimp the darn hose shut while the engine is idling. This will tell you weather or not to even suspect the IAC valve. If the idle goes down, search the FAQ for cleaning the IAC. Cleaning may or may not help, but you will have it out at that point and can check in on the bench at that point.