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> Rough Idle When Cold, Volvo 940 Rough Idle When Cold then mostly okay
volvo dan
post Sep 3 2012, 03:11 PM
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Hello,

I have a 1994 Volvo 940 and have previously owned a 740 for many years. I've only owned this car for about 1 month. The car appears to have been well cared for. Doesn't leak a drop of any fluids, everything works, and mostly a really nice old car.

What happens is that it idles rough when it's cold. In fact, I have to pump the gas pedal to keep it going. When I first start off, the performance is less than what it should be too. Once it get warm, it mostly runs fine.

I have so far replaced, the Plugs, Wires, Cap & Rotor. All the vacuum lines, crank position sensor, Air Mass Meter and the fuel filter and most all the fuel lines too. The Fuel Pump Relay was replaced but I removed it and saw a few cold solders and fixed those but no changes in performance. Before I replaced the Air Mass Meter I brought it to local shop and they returned a readout of 2-3-2 which I'm understanding means running too lean. That's why I replaced the Air Mass Meter. (I did notice a big improvement once I replaced the Air Mass Meter too.) It was interesting that when I replaced the Distributor Cap, I noticed like black carbon in there and I'm not sure what could cause that. Although, I did find the previous plugs were not all the same. Three of them were high spark performance plugs and one was just normal

I pulled the Idle Air Control Valve and plugged one side to ground and the other side to 12V and noticed the flapper moving when powered on/off. The previous owner told me he replaced both fuel pumps about two years ago. It also looks like the fuel regulator valve is mostly new.

I'm guessing now that I have a problem with the Idle Air Control Valve or perhaps the Fuel Temp Sensor under the intake manifold. I purchased the Fuel Temp Sensor and just have not installed it yet. I really don't want to remove the intake manifold but I know it's not going to be that bad. I know that it could be carbon build up on the intake valves but I'm not quite convinced yet. I put some fuel cleaner in the tank to see if that helps and so far nothing yet. The car only has 150K on it and I was told that during the owner before me did do highway driving.

When it's warm, the car does run very very well. The idle is still a bit quirky even when warm. For instance, when I power on the A/C, the idle RPM doesn't increase like I expect that it should. (It did on my 740)

I'm still thinking maybe it's the Idle Air Control Valve too. Perhaps it's intermittent or do I understand that they can gradually open and gradually close?

Any help is welcome. I'm going for the Fuel Temp Sensor next so any suggestion are welcome. Thank you!
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grendel1960
post Sep 3 2012, 05:46 PM
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on one of my volvos (440) I had a similar situation, it was the fuse for the pre heat on the oxygen (lambda) sensor that had blown, now I dont know if your model has the sensor, but if it does its worth checking, its also worth noting that the fuse on mine was tucked up under the dash - not with the rest of the fuses, once again not to sure of the 940.
Grendel
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danielm85948
post Sep 3 2012, 07:21 PM
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QUOTE (volvo dan @ Sep 3 2012, 03:11 PM)
Hello,

I have a 1994 Volvo 940 and have previously owned a 740 for many years. I've only owned this car for about 1 month. The car appears to have been well cared for. Doesn't leak a drop of any fluids, everything works, and mostly a really nice old car.

What happens is that it idles rough when it's cold. In fact, I have to pump the gas pedal to keep it going. When I first start off, the performance is less than what it should be too. Once it get warm, it mostly runs fine.

I have so far replaced, the Plugs, Wires, Cap & Rotor. All the vacuum lines, crank position sensor, Air Mass Meter and the fuel filter and most all the fuel lines too. The Fuel Pump Relay was replaced but I removed it and saw a few cold solders and fixed those but no changes in performance. Before I replaced the Air Mass Meter I brought it to local shop and they returned a readout of 2-3-2 which I'm understanding means running too lean. That's why I replaced the Air Mass Meter. (I did notice a big improvement once I replaced the Air Mass Meter too.) It was interesting that when I replaced the Distributor Cap, I noticed like black carbon in there and I'm not sure what could cause that. Although, I did find the previous plugs were not all the same. Three of them were high spark performance plugs and one was just normal

I pulled the Idle Air Control Valve and plugged one side to ground and the other side to 12V and noticed the flapper moving when powered on/off. The previous owner told me he replaced both fuel pumps about two years ago. It also looks like the fuel regulator valve is mostly new.

I'm guessing now that I have a problem with the Idle Air Control Valve or perhaps the Fuel Temp Sensor under the intake manifold. I purchased the Fuel Temp Sensor and just have not installed it yet. I really don't want to remove the intake manifold but I know it's not going to be that bad. I know that it could be carbon build up on the intake valves but I'm not quite convinced yet. I put some fuel cleaner in the tank to see if that helps and so far nothing yet. The car only has 150K on it and I was told that during the owner before me did do highway driving.

When it's warm, the car does run very very well. The idle is still a bit quirky even when warm. For instance, when I power on the A/C, the idle RPM doesn't increase like I expect that it should. (It did on my 740)

I'm still thinking maybe it's the Idle Air Control Valve too. Perhaps it's intermittent or do I understand that they can gradually open and gradually close?

Any help is welcome. I'm going for the Fuel Temp Sensor next so any suggestion are welcome. Thank you!

check for a dirty or wet throttle control module check the plug to it look at the side of your throttle.
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volvo dan
post Sep 4 2012, 12:45 PM
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Okay, so I checked the fuel pressure and it is about 38 to 40PSI. I checked it with all the vacuum lines connected. Does anyone know if this sounds right? I have not checked the fuse thing yet or the throttle sensor. I did mark it and adjust it previously and it seems to work okay. Thank you for your replies.
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volvo dan
post Sep 4 2012, 12:46 PM
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Okay, so I checked the fuel pressure and it is about 38 to 40PSI. I checked it with all the vacuum lines connected. Does anyone know if this sounds right? I have not checked the fuse thing yet or the throttle sensor. I did mark it and adjust it previously and it seems to work okay. Thank you for your replies.
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draser
post Sep 12 2012, 06:31 PM
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I'd check the coolant temp sensor - this tells the ECU to run rich when cold. It should read high resistance cold, low resistance warm. Also check the connector and circuit wires. Also the idle air control valve may need cleaning.
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danielm85948
post Sep 13 2012, 05:23 AM
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QUOTE (draser @ Sep 12 2012, 07:31 PM)
I'd check the coolant temp sensor - this tells the ECU to run rich when cold. It should read high resistance cold, low resistance warm. Also check the connector and circuit wires. Also the idle air control valve may need cleaning.

there is two sensors on the thermostat housing,cold start sensor is the top one, temp sensor the bottom one.top one controls the cold start injector which can leak due to dirt.
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volvo dan
post Sep 21 2012, 03:50 PM
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I recently replaced the Fuel Temperature Sensor (FTS) near the back of the engine. (Which by the way was not too difficult with the intake manifold in place. Not fun, but I was able to do it.) The resistance of the original FTS was 3.64K Ohms and for the new one it measures 2.68K Ohms. The problem is that when I it withthe new one the car really wouldn't start or run. I had to put the old one back in to run the car so I'm back where I started.

I am wondering now... I've read that when the FTS go bad the resistance goes up which makes the car run too rich. Does anyone know the appropriate measurement of these FTS as a new product out of the car? The one thread here reads that it should be high resistance when warm low resistance when cold. Which would make sense why the new FTS I installed with higher resistance when cold makes it run worse or not at all.


I have been talking with a Volvo Enthusiast who seems to think this is fuel related. I checked the timing and it aligns with the marks as it should. I did test the fuel pressure as stated before and it was around 38PSI with all vacuum plugged in. I have read that it should be about 43PSI. The Volvo Enthusiast has told me to let it sit with the fuel pressure gauge on it overnight and then get the reading. I'll probably do that but even if it goes to zero, from what I've read that should not matter.

I'd really like to solve this because as you can imagine it's making me very unhappy with my recent purchase. I will try those sensors near the thermostat, but I haven't seen what is spoken about yet. I'm checking again today.

Poor gas mileage too, it's around 16-17MPG, that's terrible. I have also change the intake manifold gasket and cleaned the throttle body and replaced that gasket too with know changes. The Fuel Pressure Regulator looks recently replaced but I'm curious that it could be perhaps bad? (Sigh)

This post has been edited by volvo dan: Sep 22 2012, 08:06 AM
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draser
post Sep 22 2012, 08:25 AM
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The coolant temp sensor should read about 1.7 KOhms (1700 ohms) when cold, and tens of ohms when hot. Not sure what the Fuel Temp Sensor does, did not find on Google. However, the coolant sensor is an easy check, if you have the ohm meter. Your fuel pressure is ok, based on your measurement. If you unplug the vacuum to the Fuel Press Reg and idle goes up then the regulator works.
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volvo dan
post Sep 29 2012, 07:52 AM
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Once this problem is solved, I will start a new post shorter post taking it from start to finish. One of the problems I've noticed on many forums is that people post a problem, and or question but then never come back and post their solution. I'd like to post the solution once I find it in on brief new post.

My story continues with the recent replacement of the Fuel Injection Temperature Sensor, (FTS). It is located on this 1994 Volvo near the rear of the engine, on the drivers side. I removed it without removing the intake manifold. I had a 19mm deep well socket and a flexible 1/2" driver knuckle to remove it.

It may be too early to tell but it appears that my MPG has gone up quite a bit. The problem though is that the car will crank but not start with the new FTS. I unplugged the Air Mass Meter (AMM) and the car started right away. The car has no power with the AMM unplugged so I waited a few minutes for it to warm up. Once the car was sbaomewhat warm, I can turn off the car, plug in the AMM, and then start the car.

The car still runs rough until it's warm. However, once it's warm it really run very nicely. I'm going to take another guess and replace the Coolant Temperature Sensor today, in hopes that that value is off, causing my cold starts.

To summarize, I removed the original Fuel Temperature Sensor and measured it in Ohms next to the new one. The original reading was 3.64K approximately, and the new one 2.68K. When I placed each one in warm/hot water and then removed them, the new one would read about 500 Ohms, but the old one never went down to that. It read approximately 900 Ohms. So I think the FTS was bad for sure, just not completely bad. But because of that, I'm hoping that the cold start problem now is related to the Engine Coolant Temperature Sensor for the dash.

I am guessing of course but will post the outcome as I progress.

This post has been edited by volvo dan: Sep 29 2012, 08:04 AM
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