Idle RPM drop under hard stop, 1997 850AWD B5254T

Ivo · Post by **Ivo** » 15 Nov 2007, 22:54

Hello Volvo community,

My faithful Volvo 850AWD is giving me some hard time recently. Under hard braking I saw how my rpm dropped to around 500rpm and then went up to almost 1000 and then went to the normal around 850RPM.
I noticed that when I go to a stop some times the RPM is unstable and the car hunt for the proper rpm moving between 500 to 900 RPM.

1. I attached my OBD II for a test ride and nothing

tripleb · Post by **tripleb** » 16 Nov 2007, 18:51

Some pics would be good for the vac lines, I'm not sure which ones you are describing.

It sounds like a possible vacuum leak, a slow responding idle valve, or maybe an out of adjustment idle position sensor.

Make sure the throttle linkage and cable are adjusted properly. I think you can clean the idle valve and see if it helps.

Can you read the idle position from your scanner, is it OK?

Good Luck

B

Ivo · Post by **Ivo** » 16 Nov 2007, 19:30

Hi, I did clean the idle valve - it wasn't so bad.
Do you know what are the normal values on OBDII from the idle valve and for the MAF?
I will send pictures the next time I post

tripleb · Post by **tripleb** » 16 Nov 2007, 19:36

You should have the specs in VADIS.

Ivo · Post by **Ivo** » 21 Dec 2007, 20:19

An update:

The new throtle body gasket and spark plugs are installed;
My short and long trim fuel delivery is good - it is + 1 to +4 and I know up to +8 is acceptable, so I rulled out the fuel delivery;
I noticed that when the RPM drop the reading from the MAS drops to 2.3g/s which is low. At idle the reading is 3.5 to 3.8g/s.

Ivo · Post by **Ivo** » 21 Dec 2007, 20:31

Here is the picture of my engine's front side with the 3 vacuum lines I need to identify. I put numbers to each of them to be easy for you guys to identify them. I cannot find even at Volvo the vacuum elbow that connects the metal vacuum line goinog up under the fuel rail.
Any idea - I think it is around 8mm.

Ivo · Post by **Ivo** » 21 Dec 2007, 20:35

some more pictures:

Post by **MadeInJapan** » 21 Dec 2007, 22:49

Ivo, I don't have that particular vac line on my '98 (the one you circled 1). I wonder where it goes? I'm stumped along with you on this one. I hope others can help you figure it out.

Ivo · Post by **Ivo** » 22 Dec 2007, 11:00

Hello,

Here is my wild gues: this funny trouble maker pipe goes up under the cover of the fuel rail and continues above the engine next to the fuel rail (it is one fo the 2 metal pipes on the front top left side of your engine (looking from the front of the engine))
My conclusion is - the fuel delivery system on B5254T is without fuel return line. Instead, this is a vacuum line that goes to the fuel pressure regulator, supplying vacuum to help retain the fuel pressure constant.

Any comments?

Also, please help me find the elbow - the volvo part guy looked at it and told he has no idea what part is this and he was not able to figure it our even with a half a dozen ofpictures from Vadis.
The elbow is bad - if I touch it it makes my fingers black!
I am thinking that it for ure has impact on my fuel consumption, hesitation and RPM problem.

Regards,

Ivo

bobsnow100 · Post by **bobsnow100** » 22 Dec 2007, 19:40

A partially clogged pcv system can cause this. This was what caused my wifes 2001 xcv70 to do this surging when coming to a stop. Also I would make sure the idle air valve is working properly .