I have a 1996 850 2.0litre 10valve automatic, 55000 miles.
If I start the engine cold, it runs and drives O.K. I run for about 10min to allow the engine to reach normal temperature, and then switch off. I then leave for 30min to cool.
If I then start the engine, it runs rough at idle (like an over rich mixture ), and trying to drive, it still runs rough and sometimes stalls.
Leaving it to cool overnight the same process occurs. No fault code shows on the OBDII self diagnostictest.
Any help please?

 

Welcome.

It could bea ECT.

 

+1 for ECT sensor.

Also, when was the last time for a good tune-up? Refer to my 1st & 2nd replies at:

https://volvoforums.com/m_48928/tm.htm

Happy New Year,


JPN

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[IMG]local://upfiles/6892/0F2E48922C2D47119F38014481C3CE25.jpg[/IMG]

 

Many thanks and a happy New Year to those who replied to my query.
The car was serviced and fitted with new plugs less than 1000 miles ago.
I conducted tests on the mornings of 1st and 2nd of Jan. on the ETC sensor,by tapping into its plug and socket.The outside conditions were dry and 4or 5 degrees C. On both mornings I went through the cycle of warm up to max temperature, switching off, leaving for 30 min., and finally restarting (this is when the problem normally occurs). Unfortunately, the engine ran O.K. throughout and the problem did not occur. The sensor resistance and voltage appeared to behave according to figures I found on Volvo web sites, apart from the max temp voltage being 0.4V, which may be a little high, with the instrument panel temp guage sitting at the 3.30 position rather than the normal of 3.00.
Anyway, I have ordered a newETC sensor anda new thermostat and will let you know the outcome after these have been fitted.
Finally, my wife ( who normally drives the car, due to myself becoming disabled with bad legs over the past year ) reckons the problem only occurs when the weather is damp.

 

In general, engine performance trouble during damp weather is related to the ignition system as electric current is leaking somewhere rather thanreaching the distributor/spark plugs. When were the distributor cap, rotor & the ignition wires replaced?

Will wait for your update.


JPN

 

Thanks JPN, I agree with you that the clue about damp weather would point to an ignition fault. In answer to your queries I can provide more info :-
The problem first appeared in early Dec. 2007. I got the car to the local garage, who changed the plugs, but could not cure the fault. They then took the car to a Volvo specialist. A few days later I was informed that the car was ready and running O.K. The bill, I received, showed that they had replacedthe fuel filter, distributor cap, and rotor arm, but no explanation as to what had been found to be faulty. The car was used throughout 2008, just for short journeys, without any problem, but come early Dec. 2008 the fault reappeared, with less than 1000 miles being done.
What baffles me about the problem being caused by the ignition system are the following :-
1. Theenginehas always easily started, when cold, in any weather.
2. When the fault appears, the engine behaves as though it is receiving an over rich mixture, lumpy idling and revs varyingbelow the normal800rpm.
3. The faultonly appears after the engine has been run up to max temperature, and then left to cool for about half an hour.

For the moment I will await damp weather to investigate further.

 

Did the bill include ignition wire replacement? Ignition wires need to be replaced a lot more frequently than most people think. I do mine at every 5 years/50,000 miles. This may be an overkill, but considering the relatively low cost of the wires, it is a well-spent money as far as I am concerned.

Also, did the shop use OEM parts? Volvos, as well as all other makes, are sensitive to the quality of parts. Throwing cheap parts made in God knows where is a sure way to degrade your car’s performance.

Will wait for your feedback.


JPN

 

In answer to your two queries JPN :-
1. The ignition leads were replaced 500 miles ago, summer 2008. I had forgotten about this incident. What happened was the engine started misfiring and was easily recognised as an ignition fault. I discovered that the H.T. had burnt a hole through the plastic sheath, which surrounds the plug oncyl.1.
2. I do not know what type of spares were fitted, but as the work was done by a Volvo dealer, I assume they were Volvo.

 

If it were not for the ignition components, I can only assume one of the electrical connectors for sensors may be getting loose or allowing moisture. CPS (Cam Position Sensor) connection comes to my mind.

If new ECT sensor & thermostat did not help, I would try cleaning all engine sensor connectors with contact cleaner, with the negative battery cable removed. Once the negative cable is removed, the ECU has to re-learn idle with ALL electrical loads turned off. What I do is to turn off everything, even disengage the parking brake to extinguish the brake light in the cluster, then start the engine without depressing the brake pedal and let the engine idle for 10-15 minutes. I am not sure if this is the exact procedure designed by the engine control designers but it worked for me.

I think I am missing something here. I would wait for other members’ opinions as well.


JPN

 

PROGRESS REPORT 8 Jan. 2009
This morning,damp weather has returned, after a few days of below zero and dry conditions, and so has the fault.

10.00 am :-Outside conditions were damp and foggy, with a temperature of 2 degrees C.
Engine started at first attempt and run in 'P'. Revs increased now and again up to 4000 rpm, and'R' and'D' engaged. No problem.
10.20 am :-Temp gauge reached a max of about 4 o'clock. This is significant, as it should have reached 3 o'clock
Engine turned off, and allowed to cool.

10.40 am :-Engine restarted. Temp gauge showed belowbottom of scale. Rough running was encountered.
Tickover varied beween 600 and 800 rpm, andengine stalledif agear was engaged.
Increasing revs to 2000 to 4000, no roughness showed, but at lower revs, the engine hunted between 1000 and 1200 rpm with a periodic time of 2 seconds.

10. 50 am:-Max temp ( 4 o'clock ) reached, and engine turned off.

Conclusion:- Either the thermostat or ECT sensor is faulty.

I have not yet received the replacements for these two components. Will report again after they have been fitted.

 

Success !!!
The thermostat and ECT sensor were replaced a week ago , and the car has been tested every day since , in weather conditions which have mostly been cold and damp . No fault has appeared . Testing the old components revealed a faulty thermostat which opened at 74 degrees C instead of the marked 90 degrees C . The ETC sensor resistance was found to be within 10% of the of the published figures over the temperature range 20 degrees C to 100 degrees C.
Many thanks to all those who helped me with this problem.

 

This sounds suspiciously like the problem my son's car is experiencing (shaking at startup). Looks like the t-stat should definitely be the next this to check since we have already replaced the ECT sensor.

patrick4, did your car ever have the check engine light come on through this process?

Jeff

 

Hi Jeff ,
The only time the engine warning light came on was after the local garage had replaced the thermostat and ECT sensor. They did not know how to clearit , but I cleared it ,after recovering the car ,by going through the ECU re-learn process , given by JPN earlier in this thread . No fault codes were ever detected throughout my investigations .
I do not think your problem is due to the thermostat if the temperature guage is coming up to the 3 o-clock position . I never had a problem starting from cold in a morning ( I am located in Norfolk , England where the outside temperature only dips a few degrees below zero at the most ) . My problem only appeared after the car had been left for about half an hour after a short run .