Running issues

[sirjerram]

Hello all, first time poster here so forgive.

I have a 1995 Volvo 850 10 Valve N/A with a head-scratcher of a fault.

So going back 5-6 months after having the car parked for a year I decided to do a stage 0, a full service, new timing belt and tensioner, new belts, drained all the fluids etc etc. It then had its MOT which it failed initially on a high idle (1500RPM) after taking it for a good blast I managed to get the idle down to 1300RPM, obviously still an issue. I decided to park it back up and diagnose this fault and try and correct it, upon looking further I discovered the plastic restrictor on the throttle plate had cracked which I believed had been allowing too much air flow through when idling. Unfortunately due to my partners car breaking down I was forced to use the Volvo for a 100 mile round trip and a few smaller journeys and this is when problems started occurring, I'll list them below in chronological order:

1) Upon starting the car when the engine is cold (Left overnight) the car would stall unless I feathered the throttle to around 1500RPM, as soon as I stopped the car would stall and it stayed this way until the engine had started to warm up, once the engine was warm this would disappear, however it would idle at around 1300RPM when stopped in NEUTRAL or PARK.

2) After a few journeys of the car doing the above ^^^ the symptoms manifested into another fault; instead of the car trying to stall when cold it decided to have a random idle which would rapidly flick between nearly stalling to idling too high (650RPM-1700RPM) this fault was persistent when the engine was hot or cold.

3) Unfortunately on my 100 mile roundtrip the symptoms got even worse, it started off with its random idle but after about 20 miles the symptoms progressed so that when in PARK or NEUTRAL the idle would sit around 2000RPM, once in drive the idle would be normal. This got even worse, every time I had to stop and go into park or neutral the idle would climb slightly higher than it did before....2200RPM....2500RPM....3000rpm all the way up to 4000RPM. During all of this trip the temperature needle sat perfectly at 3 0' clock, it didn't miss a beat whilst driving only during idle.

After this trip its been parked up and I have since double checked all the previous work (No faults found) I have replaced the throttle body with a genuine one with the restrictor intact - upon starting it was better but the idle sat around 1300RPM when hot or cold. I have also now replaced the IACV valve which again has helped, the idle is still high but only at 1100RPM.

Since fitting the new IACV (From a working vehicle) the car will start but will die unless I accelerate, after 5/6 seconds it idles fine at around 1100RPM. If I disconnect the IACV the car starts after 2/3 seconds and idles at around 700RPM. If I start the car with the IACV unplugged and then plug it in the car idles around 900RPM and slowly rises to 1100RPM.

I have checked the MAF sensor, the voltage seems fine and disconnecting it before starting and whilst its running makes no difference whatsoever. I will be replacing the PCV with a genuine kit in the next week or two as it fails the glove test and there is oil in the flame trap. I have sprayed brake cleaner around the whole intake system and vacuum tree and there was no spike in RPM so I do not think there is a vacuum leak.

I'm at my wits end with this car, it was an inheritance so it has a personal touch so if you're advice is bin it then please don't comment, I will be happy to answer any questions but any advice will be greatly appreciated.

[scot850]

It sounds like your coolant temp sensor is not working which I believe is the initial issue. This may well have manifested into the other issues.

Your temp sensor is built into the thermostat casing and has a couple of wires coming out of it to a connector mounted to the power steering pump bracket at the back. Both the connector and wires into the connector are known to go bad, and sitting makes them worse. You will find it regularly called the ECT (Engine cooling temp) sensor.

Check the connector and the wires to it and see how they are. If they are crusty you may have to make a wiring repair or a bypass of the connector.

There are values posted on MVS for resistance values to ambient air temperature when the coolant is cold. These can be used to check the sensor itself is good or bad.

Basically (if you are old enough!) older cars had a 'choke' device which enrichens the fuel to the engine when cold to help the engine run and as the engine warms you reduce the choke until it is off.

These Volvos can start with a high RPM setting initially but usually they reduce after a few seconds to a minute.

The other thing to check the cable for the accelerator. Again with sitting they can get sticky. Removing the cable from the throttle assembly end and try to force some oil into the sheath surrounding the cable and work some oil into the cable. These can stick and cause a high idle. Also check the flap mechanism is moving smoothly. Again oil into the mechanism and working the unit a by hand may also help.

Good Luck!

Neil.

[sirjerram]

Hello Neil,

Yes one thing to check is the ECT sensor, I've taken it on a 30 mile drive tonight to see if it needed to relearn the values but by the end of the drive it was sitting at 1500RPM in park or neutral.

The temperature guage seemed to climb normally, it started up first time with the IACV connected, temp guage was 0 as the temperature here is 3 celsius, it slowly warmed up and sat just below the 3 O' clock position - possibly around 80 Celsius for the entire journey.

I'm going to have a look tomorrow to see what codes I can pull but the Diagnostics module is temperamental (Not OBD unfortunately) and see what they point to, I'll keep the thread updated as I go.

Much appreciated,

Jacob

[scot850]

The fact the gauge gets to around the 3 o'clock would suggest the ECT is working, but I would still check the resistance values and connector as this will also affect the engine cooling fan operation.

I would then check the throttle flap and cable are lubed as suggested and we can go from there. The 'normal' idle speed should be in the 850-900 RPM range.

Neil.

[abscate]

Morning Jacob

(Translation for the Colonies, binning a car doesn’t involve programming, but the junkyard instead)

You can’t use the temperature gauge as a test for the coolant sensor. It’s a very coarse measurement tool, I think I documented it here somewhere. The ECU has to precisely meter the fuel according to engine temperature, injecting 3-5x more fuel when cold than when hot.

Make those resistance measurements in ice water and hot tap water!

Grabbed screen shots , you can use titles to search fir more info

[rspi]

[sirjerram]

Morning Jacob

(Translation for the Colonies, binning a car doesn’t involve programming, but the junkyard instead)

You can’t use the temperature gauge as a test for the coolant sensor. It’s a very coarse measurement tool, I think I documented it here somewhere. The ECU has to precisely meter the fuel according to engine temperature, injecting 3-5x more fuel when cold than when hot.

Make those resistance measurements in ice water and hot tap water!

Grabbed screen shots , you can use titles to search fir more info

Hello mate,

You say make the restistance measurements in ice water and hot tap water, are you saying to disconnect the sensor from the thermostat? Do I check the resistance at the plug or on the sensor itself?

Cheers,

Jacob

[sirjerram]

The fact the gauge gets to around the 3 o'clock would suggest the ECT is working, but I would still check the resistance values and connector as this will also affect the engine cooling fan operation.

I would then check the throttle flap and cable are lubed as suggested and we can go from there. The 'normal' idle speed should be in the 850-900 RPM range.

Neil.

Hello Neil,

I'll do the tests on the ECT sensor and will lube up the cable and throttle plate, would aerosol White lithium be best or a tub of Molly greese?

Cheers,

Jacob

[erikv11]

Morning Jacob

(Translation for the Colonies, binning a car doesn’t involve programming, but the junkyard instead)

You can’t use the temperature gauge as a test for the coolant sensor. It’s a very coarse measurement tool, I think I documented it here somewhere. The ECU has to precisely meter the fuel according to engine temperature, injecting 3-5x more fuel when cold than when hot.

Make those resistance measurements in ice water and hot tap water!

Grabbed screen shots , you can use titles to search fir more info

Hello mate,

You say make the restistance measurements in ice water and hot tap water, are you saying to disconnect the sensor from the thermostat? Do I check the resistance at the plug or on the sensor itself?

Cheers,

Jacob

For these measurements you remove the sensor and bring it into the kitchen. Be careful unhooking the connector, it is notoriously crumbly. You'll lose a little coolant unless you drain some out. Check R across the plug socket.

I like to use boiling water for the hot (100 ˚C) measurement. As the water cools you can check some intermediate temps too if you have a thermometer nearby.

The fact the gauge gets to around the 3 o'clock would suggest the ECT is working, but I would still check the resistance values and connector as this will also affect the engine cooling fan operation.

I would then check the throttle flap and cable are lubed as suggested and we can go from there. The 'normal' idle speed should be in the 850-900 RPM range.

Neil.

Hello Neil,

I'll do the tests on the ECT sensor and will lube up the cable and throttle plate, would aerosol White lithium be best or a tub of Molly greese?

Cheers,

Jacob

Best way to service the throttle plate is to pull off the plastic tubing and clean the metal surfaces of intake snorkel and flap with carb cleaner and rags. I've never followed cleaning with grease or lube, I think that might just attract grime and gum it back up. You can check for smooth operation by hand once it is cleaned. Be careful to not get carb cleaner into the TPS, a little black box sensor mounted on the underside of the throttle. One way to ensure that is to remove the TPS before the cleaning job but you can leave it if you're careful.

I've never lubed the throttle cable, seems a good idea that white lithium grease would work for, that's a common way to service bike cables. May want to get the cable out of the sheath to do it thoroughly.

[scot850]

White lithium may work. For the throttle mechanism I would first use something like WD40 and work the mechanism back and forwards several times. Then wipe of any excess and then lithium grease. Lithium grease is too thick to get into the shaft to get it lubed. A thin oil is what I would use on the cable as I am not sure you can remove the cable and get to lube it properly.

Follow Erik's advice on cleaning the throttle plate. I use throttle cleaner but on a rag so as not to cause issues with the TPS.

Neil.