96 850 turbo underboost/overboost

snugani · Post by **snugani** » 23 Aug 2025, 10:21

Hey guys. I've been having some issues with my turbo. I replaced the three lines going from the tcv to the turbo right after I got the car. I noticed they looked pretty crappy. It felt like it might have been overboosting slightly.

After replacing it the gauge only goes about a quarter of the way when flooring it and I don't feel much boost. Whats weird is it will sometimes randomly go almost all the way to the end, but much less often. I'm not sure if this is overboost or where it should actually be going.

I've got a new cbv from ipd on the way, but is there anything else I should be checking? Im thinking it could be the tcv or even the actuator itself. The car has about 100k on it. Also, how far should the gauge be going under full boost normally? I've been driving with a light foot so I don't bend a rod if it decides to overboost

Post by **Sveedy** » 23 Aug 2025, 13:39

I would replace the TCV. Get the Pierburg one. Do not get the IPD one. Check and recheck your vacuum line set-up.
As I recall, the dash boost gauge doesn't go much above 3/4 when stock.

snugani · Post by **snugani** » 23 Aug 2025, 15:43

Thanks Sveedy. I'll probably order one tonight if this cbv doesn't fix anything. Yeah I've heard the ipd one isn't good, especially for the price

Post by **scot850** » 23 Aug 2025, 17:37

The IPD one is better than stock for higher boosts, but for a standard car use the OE Volvo or Pierburg as Sveedy says.

The main issue with the IPD one is the crappy design of the unit. You have to turn the plastic leg that goes into the front middle fitting no more than 3-4 turns. Don't turn it all the way is as it crushes a small filter onto the valve jamming it. It is a stupid design, I have told them to clarify this on their paperwork, but still nothing done. In practice when fitted correctly it works.

As Sveedy says, also double check you got the hoses on correctly. You may have fitted them as they were, but they may have been fitted wrongly before you got the car. There used to be a small graphic of the pipe routing on the underside of the hood. It can be found on-line as well.

The boost might need adjusted or may be sticking. Or the diaphragm might be failing in the CBV.

Don't be tempted to go with the higher spring rate in the IPD kit on a standard engine.

Good Luck!

Neil.

Post by **jreed** » 24 Aug 2025, 06:43

I don't own one of these IPD TCV's but I noticed that IPD updated their installation instructions with a warning not to overtighten the fittings:

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