i have 760 turbo 85 model but i dont know it runs i bought it 2 months ago not knowing anthing about volvos i am a holden man but anyway i have bought a haynes manaul which is ok for somethings but bad for others but my question is the car has had a wire melt down which the previors onwers replaced the loom but the iac dosnt work and the o2 senor is not there at all.
fuel consuption not very good it has a motronic ecu in it but the wiring diagrams dont show the o2 senor and where it connects to.
also is there a pin on the ecu that conects to the iac so i can check it to make shore that there is no shorts.
all help would be great as i have learnt a lot so far reading from this site
thanks Lindon

Are you in the states? An 85 doesn't have a motronic set up over here. It has a jetronic set up.

Chris

i am in australia but i have found some more info on it which pins etc to check the wiring and ohms
i will keep looking checking etc this weekend
thanks lindon

Hi Linden,

The Motronics ECU systems do NOT seem to have an O2 sensor or Idle Air Control (IAC) Valve (see link - need to scroll). There is a CIS unit involved - not sure what that does though...

Noel

how do I access the site from that link, I'm looking for info on 89 740 turbo

You just needed to click on that link. Anyway - click here to access it.

If you still have a problem with that link, copy the link below to your browser and use it

http://www.autoelectric.ru/auto/volvo/740/1989/740-89.htm

Noel

hi noel
how about if i take a picture u may be able to tell me what it is
it basic has 3 pin connector on it with 1 pipe comming from the manifold intake and 1 from the intake from the air filter if i ground out the outside pin the revs jump up to 1500rpm disconnect it back down to not very good
i will play with it this weekend again as i have found some tests i can do to find out if i have a short or some more $$$$ i have to spend.
i will keep u updated
regards lindon and thanks again

Hi Linden,

From your description it is obvious you DO have an IAC, and that it is working in the fully-open and fully-closed position. However, it's more important that it be working (and can be controlled accurately by the ECU) in the partially-open position - since that's where it spends most of it's life in. That's what I found with mine: it worked fine when I shorted the extreme connectors to ground, but was still causing a high idle. I opened it and cleaned the commutator and spindle, and the high-idle went away (see this post). The above thread also has a lot of valuable IAC info from other more-experienced members.

By the way - when you say 'my IAC dosn't work' - what exactly do you mean ?

Another thing to check before you open up that IAC is if you are getting any voltage at the IAC-connector end. If the IAC connector-rubber-boot is split like mine is, you can check this without unplugging the IAC connector since you have access to the back of the connector-terminals. If it is not split, remove the connector and check that you receive voltage between center and extreme terminals with the engine running.

If you do not get any voltage, you have a problem with the wiring. If you do
see voltage, you could still have a wiring-harness problem if one of the wires are shorting with ground somewhere (since that's sufficient to fully open or close the IAC). Make sure you check your wiring for crumbling insulation and shorts before you open the IAC. The way I did it was remove the ECU connector and check for continuity and possible-shorts of each and every wire. I also checked the following at the ECU connector end to verify that all signals were getting through to it:

- plugged the IAC in and measured the coil resistance of both coils
- checked coolant temp. sensor resistace (verify it matches sensor resistance)
- checked working of the TPS switch
- checked continuity of the CO and idle-setting test-leads
- AMM resistance (verify it matches resistance at AMM end too)

Let me know how it goes. Also explain in detail what your IAC problem is that leads you to believe it dosn't work.

Noel

hi noel
had a play with it this weekend and traced the wiring and found no shorts
when i traced the wiring it goes to a large black box which in the manual they call it lfr system no idea what that means.so i found that there are no shorts from b box to the iac valve and i know that the iac is working because when i ground the white wire from the iac the revs jump up to 2400
also they say there is cis temperature sensor to control it but i can only find 3 1 for the thermal time switch,2 temp gauge,3the 1 under number 3 intake which connect to the climent control so i am at aloss
what the iac is doing when i start the car i have to use the gas pedal to start it and to keep it going but after 5 mins it will idle normally
buy the way when i had the iac off i cleaned it and put the connector on and turned the key on it just closes hot or cold but there are no shorts i even when to the point of running new wires from the bbox to the iac with the same result i did the test from the motronic box for the tps,amm,air flow meter fly wheel senor etc but they are all ok. so i am wondering if that cis temp senor is at fault buy the way they call the black box cis control unit i will keep hunting and might ring a volvo dealer and ask him about this senor.

thanks lindon

I can think of 3 things you can try:

1. Measure the resistance of that temp-sensor when cold. Depending on outside temperate - cold temperatures range is between approx 2000 - 6000 ohms. You need to check that it is not measuring <100 ohms or thereabouts, because that would indicate a hot engine to the ECU. (more info here). When measuring resistance, verify this at the ECU (or CIS control) end as well

2. Rig up this test LED setup and hook it up to the IAC wiring - preferably without disconnecting it from the IAC. This would give you an approximate idea of how the ECU is controlling the IAC. The green LED is for the opening-coil, Red is for the closing coil.



When you start a cold car, the ECU forces the IAC to fully-open for about a second after start, after which it slowly brings it down to partially closed so RPM is around 750 or so. You can try verifying this via the LEDs. Both LEDs might glow all the time: you should concentrate more on LED brightness to help indicate the IAC position.

Another more effective test is to remove the IAC and block both hoses going to it (I bridged them with a solid-rod to take the place of the IAC). Open up (unscrew) the black idle-thumbscrew almost completely (otherwise it will not idle). Connect the IAC to the connector so you can watch the valve open/close in real-time. Now have someone switch the ignition switch ON. On my car the IAC fully opens at this point. Next have the car started and see what happens. It should slowly start closing - but not completely. If you race it slowly, the valve should slowly close.

3. If the IAC dosn't behave as expected, and the LEDs show both coils are receiving voltage - connect a multimeter between the opening-coil and slowly open up the valve manually (eraser-end of a pencil). Check to see if the resistance stays the same without jumping (which would indicate a dirty commutator and/or bad commutator connection). Do the same for the closing-coil. If you get some wild readings, I would suggest opening up the IAC and cleaning it out (I've posted how I did this - and there are a couple of other posts on the board as well). You might want to get a spare from the junkyard before doing this...

Good luck. Getting all those gremlins out of a suspect IAC can be very frustrating !

Noel

hi noel
it sure does has a iac but the o2 sensor has got me stuffed
the iac is getting 12volts to it to the centre pin.
if ipull the connection off give it power then ground the iac it will work so i guess that i will have to double check the wiring and trace it back. i might ring a volvo dealer see what they say and by the way thanks for link i have all ready check there i got it from i of your post in the past and thanks for taking time out to answer my post
thanks lindon

Hi Linden,

Thats wierd. The wiring diagrams dont show the IAC.

Anyway, how do you know the IAC is not working ? What are the symptoms ? You could try tracing the wiring by the colors from the IAC to the grey-connector, and then from the connector to the ECU. The wiring-colors are typically the same on bothe ends of that grey-connector.

Noel