Angus242164
Based on that it definitely sounds like an air issue, eg: idle control motor not working as the revs drop when the throttle closes, or a vac leak that's too big for the idle motor to cope with.
Vee_Que
Yeah, no bov and an insta spool ball bearing turbo. the hoses for the iac could be dead though
egads
Brake booster check valve can be a pretty big leak can't it?
Angus242164
Check valve won't cause a leak, but an internal leak in the booster is possible.
To test, clamp off the booster hose with pliers, while the engine is idling.
Diverdonny
Okay so vacuum leaks are ~mostly~ ruled out as I hooked up my homemade pressure rig and sprayed sudsy water everywhere while pressurising the system and only found one small leak. So obviously problem still exists.
I've ordered the TPS anyway so hopefully it'll arrive before the weekend. Also going to try pick up another IACV from the wreckers if I can find one and replace the distributor cap, rotor, leads and plugs since I don't know when they were last done except the plugs which I did 6 months ago but are probably stuffed now.
I can hear a small exhaust leak around the turbo/dump somewhere too that I'll need to pull the dump pipe off to find, if fresh air is getting pulled into the exhaust upstream of the O2, that could definitely cause this issue. Any tips for tracking it down? I'm finding this whole exercise invaluable for getting to know the car inside out so I don't mind it too much hunting down this stuff.
Vee_Que
The exhaust won't be a Cause of this issue, probably needs the v band clamp tightened and if its after the o2, makes no difference.
I have an lh 2.4 iacv.
Still points towards the no bov issue :( only way to prove that is to weld a fitting on and use a dual type bov.
egads
You could borrow one and put one in some ag pipe to diagnose maybe
Diverdonny
Tightened the V band and flange bolts up but can still hear a "pff pff pff" with the exhaust pulse from somewhere near the back of the turbo. Will probably pull it on the weekend for inspection just in case. Hopefully TPS arrives before the weekend and I can get stuck into that.
There's definitely no change to idle when the IACV is unplugged but it works fine when jumped straight off the battery. What sends it the signal?
Vee_Que
There is a gasket on the back of the turbo, so make sure you have a replacement ready.
Does the idle raise when you put the ac on? If so, the iac is working fine. But the hoses to it can suck in under vacuum too.
Angus242164
The ECU controls the idle valve, using pulse width modulation. It only opens the valve and starts controlling it's position when it receives a signal from the TPS, to show that the throttle is closed.
Agouti
From my 2JZ days (I know very little about Volvo engines as yet):
BOV delete won't cause any of the issues you have mentioned. A BOV does nothing until you come off boost. It can cause compressor surge on closing of throttle - for example when you boost -> change gear -> back on boost. Typically manifests as "choo choo choo" noise and hesitation. Popular opinion is it is also bad for your turbo but I've also seen that disputed. YMMV. If you had a BOV installed and it was incorrectly set or not closing properly it can cause vacuum/boost leak issues.
Have you checked your plugs? There is a black art to reading them but they can give you information on what is happening. There are many guides out there with pictures to help identify things.
I would absolutely be checking TPS, but I don't know how you check it (OBD?).
That 223 IACV error code is probably something to fix before moving on. Googling it seems to find plenty of people with similar issues and that same code. Have you continuity checked the plug and wiring? Checked for wiring damage? I don't know if your test is enough to verify that it is working correctly as it is not clear how the ECU reads the position of the IACV.
Your poor power delivery might also be MAF related. If you haven't already give your MAF a good clean with carby cleaner or such. Does the 940 have the adjustable MAF sensor? If so that could be incorrectly set and causing mixture issues. I would also check the operation of the wastegate actuator as if it was sticky it might cause the surging and such on boost.
goodenough
I have a 940 turbo also with the same problem did you resolve your problem?