Volvo: 850AWD engine start/idle problem, 5w30 oil, vacuum lines

Question
Hello,

I have 1997 Volvo 850 AWD B5254T engine at 217,000 km, standard transmission.
Recently the following 2 problems appeared:
1. After a sudden emergency stop, the RPM drops to 550- 600 RPM and then is shoots to 950rpms and after that it stabilizes. It happens at any weather conditions with any quantity of gas in the tank and only if the engine is at normal operational temperature;
2. The cold engine start is different compared to before – the last 3 – 4 days ( it is -18C here in Alberta, Canada) after I start the engine (no block heater on my car), the first 2 – 3 seconds the engine shakes like the RPM is too low or some of the cylinders is not working properly and after that the engine works fine.

Can you, please, advise if the 2 problems are related and what can be done to fix them?

Here is what I did so far:
1. No codes or frozen frames at this time on my OBDII reader;
2. New synthetic 5W30 oil and Man 917 filter;
3. New spark plugs BOSH;
4. Ignition wires and distributor cap are on 17,000 km;
5. Idle air valve and throttle body are cleaned a week ago (new gasket for the throttle body);
6. New air and fuel filter;
7. New vacuum lines;
8. Cleaned the intake air hose between the turbo and the MAF sensor;
9. Cleaned the MAF sensor (it is a hot film type and it was not dirty);
10. The MAF reads 3.7 to 3.9 g/s at idle (slightly fluctuating)
11. RPM at idle runs at 840 (fluctuates from time to time to 810 rpm);
12. PCV was cleaned 25,000 km ago;
13. O2S – the front one runs when driving between 100 to 790 v. (up and down – not very fast – a second between the peak and the drop value);
14. The rear O2S is having a smaller amplitude of the fluctuation;

Any suggestions if this is fuel delivery problem or ignition problem?

Regards,

Ivo  

Answer
Ivo,
Since there are not any fault codes I would suspect that there is a fault with injectors not spraying well or lower compression in a cylinder or two. Make sure that the fuel pressure is correct and that the fuel regulator is not leaking. I have heard of some problems where the valves have some deposits on them and the carbom absorbs the fuel make a hard to start and rough running engine until it warms.