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So my 1994 940 threw a 3-1-1 code the other week, and since then, the idle has been rough & my fuel milage is junk. Starting cold or hot it will idle at 600 then “lope” like it wants to cut off. Pressing the accelerator it will stumble & be choppy for a second then rev up. Let off the accelerator and it will take a few seconds to idle back down. While driving it will randomly stall out when taking off from a stop. Fuel mileage has gone from 26 to about 15 and it smells super rich. Ive checked the coolant temp sensor, and I’ve cleaned the Idle Air Control Valve. I also swapped the IAC from another Volvo I have that runs fine with no change in my symptoms. I’m really bad at diagnosing these types of issues so any help will be much appreciated.
when you say, 'i checked the coolant temp sensor', did you run an ohm meter test of either pin to the shell of the sensor, with it cold and after dunking it in very hot water ? or, with it still in the car, and your engine hot, measure the resistance from each pin to engine ground, then wait for the engine to get cold, and do it again ?
I'm asking because just saying you checke dsomething without giving a methodology, for all we know, you looked at it and decided it looked "OK".
air leaks in the intake path between the MAF/AMM and the intake manifold are the commonest cause of your symptoms. or cracks in those rubber hoses the IAC is connected to.
My apologies for the confusion, I should have been more clear on "checking it". I removed the sensor from the vehicle to ohm it out. I've checked it at 68 degrees(temp outside when I removed the sensor), and I've put it in the freezer to check it at a freezing temperature. I still need to boil some water to check the very hot end of things, but the other 2 tests showed normal results. I used numbers a write up you did on ohm values in another rough idle/no start thread. Is there more than one coolant temp sensor on these engines? I seem to remember someone saying that there is one for the computer & one for the gauge on the dash. On the intake, I will have to take a look and see if I can find any leaks.
there are indeed two. one of them is single pin, and that runs the dashboard gauge, the other has two pins, each of those pins is a seperate temp resistor to ground, one pin goes to the ECU (fuel injection) and the other pin goes to the ICU (ignition).
My apologies for the confusion, I should have been more clear on "checking it". I removed the sensor from the vehicle to ohm it out. I've checked it at 68 degrees(temp outside when I removed the sensor), and I've put it in the freezer to check it at a freezing temperature. I still need to boil some water to check the very hot end of things, but the other 2 tests showed normal results. I used numbers a write up you did on ohm values in another rough idle/no start thread. Is there more than one coolant temp sensor on these engines? I seem to remember someone saying that there is one for the computer & one for the gauge on the dash. On the intake, I will have to take a look and see if I can find any leaks.
an out of range Ox sensor would almost certainly throw a Ox sensor specific code.
I don't know - codes come and go. When my fuel return line to the charcoal canister popped off, I got terrible mileage, yet I didn't get any codes. And the car still drove well. With all his drivability issues shouldn't he get some kind of code, besides the speedo code?
Testing ECT Sensor without removing it from block/head
you can check/ohm your ECT Temp sensor by back probing the wires on the back of the ECM / ECU harness plug located behind the passenger right kick panel.
Snip the zip tie holding the plastic cover over the plug connector at the ECU to expose all of the wires and back holes of the Plug into the ECM.
You can view/print download some simplified ECM/Engine wiring diagrams for various model years, Engine (b230 b21FT, b23F, and ECM types (LH 2.2, LH2.4 vs Regina etc) here: https://www.prancingmoose.com/volvoh...l#pinfunctions
I have attached the .pdf for 1989-93 Volvo 240 with LH 2.4 ECM
The ECT has 2 terminals, one terminal of ECT wired to the ICU pin#2 other terminal to ECM Pin#13
In this case, Ohming the resistance from the specified PIN# of ECU/ICu to ground will essentially tests the entire circuit from ECM/ICU to the ECT sensor, through the block and engine grounds back to the ECM/ICU
Note: Pin# may vary by ECM and model year and Engine 89-93 volvo 240 ECU Pin functions LH2.4 ECU
This shows the pins from various sensors, but note the pin and wire colors for ECT sensor to ignition control module and also to LH 2.4 ECM... Pin #'s are noted also.
I PLAN ON USING THESE MYSELF SOON, I HAPPEN TO BE RESEARCHING THIS SO i DECIDED TO SHARE ON THIS THREAD... Hope it helps others.
03-28-2018, 05:39 PM
940 N/A rough idle, poor mileage, etc...
Testing ECT Sensor without removing it from block/head
