850 Turbo Slightly Rough Idle

[jragone]

With all the electrical work you've done, I'm assuming that this may have happened at least happened incidentally, but have you performed an ECU reset on the car? I'm also battling a rough idle in my 1996 GLT. I feel it's a lot of little issues adding up—nothing you haven't tried—but I do find that I need to perform a reset after making a change. Otherwise, it feels like the computer's already learned to sit uneasy at idle, so it's hard for me to gauge if my changes have any effect. Worth noting that for me, it takes in the tens of miles to relearn, so it's necessary to wait to assess the idle until after the learning period completes.

I'm interested to see if you find the head gasket to be the culprit. I had a brief overheating episode this past summer and have been living in blissful ignorance that my gasket is still well and good

[ZionXIX]

With all the electrical work you've done, I'm assuming that this may have happened at least happened incidentally, but have you performed an ECU reset on the car? I'm also battling a rough idle in my 1996 GLT. I feel it's a lot of little issues adding up—nothing you haven't tried—but I do find that I need to perform a reset after making a change. Otherwise, it feels like the computer's already learned to sit uneasy at idle, so it's hard for me to gauge if my changes have any effect. Worth noting that for me, it takes in the tens of miles to relearn, so it's necessary to wait to assess the idle until after the learning period completes.

I'm interested to see if you find the head gasket to be the culprit. I had a brief overheating episode this past summer and have been living in blissful ignorance that my gasket is still well and good

Ive unplugged the battery multiple times through this process. Yesterday I went for a long drive. Probably racked up 75 miles on a mini road trip to bucees and back. No changes thus far.

I did use a chemical headgasket tester abd the fluid did not change color so it seems for the moment I have an intact head gasket.

In other news the brand new brake pads and rotors are make a vibrating grinding noise that shakes the front end when the brakes heat up after a few in city stop maneuvers. I am now investigating warped rotors or out of spec wheel hubs.

And I installed a strut bar I never thought would arrive.

[ZionXIX]

A few people have suggested that I replace the turbo control valve. I had no reason to think it was broken but I decided to replace it anyway. This model is no longer available anywhere including rock auto. So IPD HD TCV is your only option. Install was about as easy as one could expect.

I did not expect to see much from this upgrade but I am now boosting better than I have ever seen in all my years of driving this car. At WOT I used to max out at 2/3 of the boost gauge. Now Im hitting the blow off valve and maxing out the gauge. I think it may be over boosting a bit but I dont know without a real boost gauge. I almost dont care because I can hear the turbo and I feel like I driving a jet fighter now. 60mph to 90mph feels amazing. Its making me consider changing the TCV on my 2005 xc90 that also has a variant of the 5 cylinder turbo.

Idle is unchanged but here we are.

Also as a side note my fuel pressure gauge is now holding at 35psi instead of 40. That seems too low now. I may have to revisit the FPR +/- the fuel pump.

[scot850]

35 psi is a little on the low side. 43 psi is the standard for the -98 cars.

Glad the boost is improved. The standard TCV is only good to about 12 psi reliably, and around 14 it gets flakey. I have a IPD unit fitted as my car was tested at Volvo with the Rica tune as boosting around 20 psi. The only issue I had with the IPD TSV is the stupid design. Despite me recommending they make clear install instructions to not screw the front plastic leg in any more than 3-4 full turns, they still have not added it. Much beyond that it contacts the internal valve and as I and others have found it damaged the valve causing it to become erratic or stick. They replaced mine under warranty. It is so annoying when they know there is an issue and do squat about it.

Neil.

[abscate]

Pier burg 915536 should fit and still be available , they OE for Volvo

[ZionXIX]

35 psi is a little on the low side. 43 psi is the standard for the -98 cars.

Glad the boost is improved. The standard TCV is only good to about 12 psi reliably, and around 14 it gets flakey. I have a IPD unit fitted as my car was tested at Volvo with the Rica tune as boosting around 20 psi. The only issue I had with the IPD TSV is the stupid design. Despite me recommending they make clear install instructions to not screw the front plastic leg in any more than 3-4 full turns, they still have not added it. Much beyond that it contacts the internal valve and as I and others have found it damaged the valve causing it to become erratic or stick. They replaced mine under warranty. It is so annoying when they know there is an issue and do squat about it.

Neil.

I need to put a proper boost gauge in. Even if Im overboosting now, im really loving the acceleration. Im not sure I would want to fix it.

[ZionXIX]

Pier burg 915536 should fit and still be available , they OE for Volvo

Do you think this would work in my 2005 xc90 with the 5 cylinder turbo engine?

[abscate]

I’m sure the p2 boost valve is different , the one above is a 98 99 only. We are so special, Prince wrote a song about us.

[ZionXIX]

I’m sure the p2 boost valve is different , the one above is a 98 99 only. We are so special, Prince wrote a song about us.

When looking at the OE version for the xc90 2.5T, on FCPs website there was at least 1 review saying it works on their 850. So maybe that would be an option for someone.