1997 850R Boost surge while cruising

Tumbler · Post by **Tumbler** » 12 Sep 2014, 00:03

Hi there,

I have an 1997 Volvo 850R with the following mods.

An IPD TCV, IPD CBV, 19T full 3 inch exhaust and a tune. I had the car off the road for 3 months while I lazily completed a timing belt change. The timing belt went great, I checked the timing 5 times and took it around the block everything works wonderfully.

The issue is that I had it on the highway (first time since timing belt) this evening just cruising and I would randomly get a boost spike while cruising. Once I pulled off the highway I also had an surging/dipping idle that corresponded with the boost spike at idle. Now the car has a random boost surge at all times. I have no check engine light on. I have a gone over every single vacuum line and they are all good. I've also checked for leaks by spraying some MAF cleaner around all the intake piping to be sure (I know not safe). I'm desperate HELP.

Also the car will get into full boost but it seemed sluggish and lacked immediate throttle response. I am sure that the timing is correct.

Thanks!

Post by **timmybdaddyof3** » 12 Sep 2014, 01:27

it does sound more like a vacuum issue....
everyone can feel free to hate me for this next one, and all of the usual disclaimers apply, and I know its not proper, totally safe, etc. The proper way to check for vacuum leaks is with a smoke machine (and even home built ones work pretty good), the redneck way (which can be done with success) is to use starter fluid (or ether) with the motor running.....it is much more flammable than MAF or carb cleaner...AND IT DOES NOT TAKE A LOT TO SEE THE RESULTS.

***I am only putting this out there because it sounds like you are on the right track, but are searching for a needle in the hay stack**** be careful and use at your own risk

Post by **rspi** » 12 Sep 2014, 08:15

How old is the blowby valve diaphragm?

Tumbler · Post by **Tumbler** » 12 Sep 2014, 08:21

I'm sorry rspi, I'm not familiar with that part would it also be called the Compressor Bypass Valve? if it is I would say less than 2 years. I also did a full PCV replacement less than 2 1/2 years ago.

Thanks for your replys!

Post by **scot850** » 12 Sep 2014, 23:49

How old is your IPD TCV? Is yours one of the newer ones with the 3 plastic 90 degree bends or the older one with the brass pipe fittings?

Reason I ask, is that with lack of specific info, I turned the front (middle?) plastic bend in too far and if you do, it compresses the little gauze filter which can cause the tcv valve to jam. I found out the hard way!! Don't turn that bend in more than 4 turns (and yes it will feel loose). Result was sluggish boost and poor/late boost.

Neil.

Post by **tryingbe** » 13 Sep 2014, 07:30

Tumbler wrote:I am sure that the timing is correct.

Never assume anything when diagnosis a car.
Check everything.