96 850 turbo idle issues

volvo850black · Post by **volvo850black** » 15 Jan 2012, 13:53

When sitting at idle, the idle will fluctuate it will start out at a bit above 1k rpm then will drop well below 1k rpm ad try to stall. Also when it accelerates it will buck (hesitate and surge) . If you let it even out and accelerate extremely slowly it does better, but if you pull to a stop it will die unless you keep one foot on the accelerator and keep it going. Please help with diagnosis.
MattC

Post by **rspi** » 15 Jan 2012, 16:03

Do you have a CEL? If so, what are the codes?

volvo850black · Post by **volvo850black** » 15 Jan 2012, 17:32

The only CEL is for low compression in one cylinder which I knew about (burnt valve) and was not causing the stall. I don't have a code reader. I went to auto zone and had them check it.

senna · Post by **senna** » 15 Jan 2012, 18:42

Check fuel pressure regulator valve, clean iac valve and throtle body.

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volvo850black · Post by **volvo850black** » 15 Jan 2012, 18:43

Where is the fuel pressure regulator located and how do I check it.

senna · Post by **senna** » 15 Jan 2012, 19:09

The fuel pressure is located between the 1st and 2nd injector behind the fuel rail. From the bottom side of the valve you should have a ruber connector to a white thin tube and it passes trough the intake manifold and is connected to a vacuum tree. Dosconect it and close the opening port in the vacum tree, put a bolt to the both ends and test it. If you have gas driping from that end your car have the diafragm of the valve broken.

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Post by **jblackburn** » 15 Jan 2012, 19:10

Does it run any better without the mass airflow sensor connected at all?

The burnt valve COULD have something to do with this - it could have fouled the front O2 sensor.

If you can put the car into open loop mode by confusing it with the mass airflow sensor, and it doesn't run better with the MAF from the other car, that may be what to point fingers at.

The fuel pressure regulator (on a 98, anyway) is just in front of the steering rack on the passenger side (this changed after the 1995 model year, where it was in the location above). Disconnect the vacuum line into the side of it and smell it and/or look for wetness in the line.

senna · Post by **senna** » 15 Jan 2012, 19:14

No errors found in my ecu...do you have smoke from the tail pipe?

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volvo850black · Post by **volvo850black** » 16 Jan 2012, 20:38

No smoke still stalling changed MAF no change unplug MAF no change. Going to try cleaning throttle body and IAF sensor is there anything else you would clean. It was running ok before I found several vacuum hoses loose and bought more hose and replaced it all. Then it started stuttering. Thanks everyone for your help.

volvo850black · Post by **volvo850black** » 17 Jan 2012, 16:47

I have cleaned the IAT and Throttle body (they were nasty). The issue sems worse now when driving the "bucking" is almost constant. When accelerating it will pause then surge. At idle it will start trying to idle at 850 RPMs then slowly creep to about 1.5k and drop back to 1k try to stall ther surge up to 1.5k and so on. Gonna go through all of the vacuum lines again as when this started was upon replacing the three vacuum lines that attach to the plugin on the side of the air box. Any other ideas on what to check is appreciated.
MattC