Diverdonny
Okay so I've got a 1993 940 Turbo. After giving it a few upgrades and converting to manual, it's got an issue with stalling out when coming to a stop, and has "odd" power delivery (think slight surging through the rev range)
I've done a lot of reading on it, but went ahead and did the obvious one first and replaced the O2 sensor. No change. Next I read up on it possibly being the engine coolant temp sensor so I swapped that out. No change. Replaced the current AMM with a 960 AMM just in case, no change. Replaced all the vacuum lines I can see to replace today and no difference.
The PCV pipe that runs back to the intake is currently venting to atmosphere; but I can't see that having any effect. I'm just after some more ideas of where to look next for something to solve it. I don't mind replacing things willy nilly since my stage 0 was somewhat half-hearted so I'll work at any suggestions and if I happen to fix the problem I'll be doubly happy.
Diverdonny
May be worth mentioning that I'm not running a blowoff valve but so far as I know, that would create the same problem anyway unless recirculated. I don't really want to look at doing that until it's one of the last options as it'd necessitate some fairly extensive custom work on my already-expensive intercooler piping.
Philia_Bear
Checked adjustment and function of tps?
Diverdonny
Voldat looked over and adjusted it when I first bought the car but I'll re-check it. May be different now that all these things have changed. For the record, idle is fine when started and stays steady as a rock until it's driven on boost. Then it'll stall, but once restarted it idles fine until entering boost again.
Angus242164
If the PCV fitting on the manifold has been capped and the vapour hose is venting to atmosphere it shouldn't cause any problems, is that how it has been disconnected on your car?
Is the idle control motor actually working? Unplug it while the car is idling and see if the revs drop or not.
Diverdonny
Okay so the idle control valve seems to affect nothing whilst I unplug it. Makes no noticeable difference. Gonna pull it off and blast it with carby cleaner and see what happens. I also had that cleaned in January when I first bought the car so I wrote it off as not a potential cause. Might be a lead to follow!
Diverdonny
Well it's still very clean inside and hardly any crud came out, but testing the voltage at the plug on the idle control valve.. There's 12V with power on, but no difference in reading when the throttle plate opens. Would this indicate a dicky TPS?
Diverdonny
Okay. Levered the throttle plate open and tested voltage at the pins on the TPS with the key on but motor not running. Got zero readings across sny of the 3 pins. Same as with the throttle plate closed. Do I need the engine running for a reading here or have I found the culprit?
Angus242164
You shouldn't need the engine running, just the ignition on as you have done. You'll need to look at a wiring diagram to see how the TPS works, I think it switches a voltage to ground, if I'm right, I would expect to see a voltage on one pin of the connector (could be 12v or 5v) and ground on another pin.
If that's what you get, you should be able to put a multimeter across the two corresponding pins on the TPS, and get continuity with the throttle closed, and open circuit once it starts to open.
Diverdonny
I get nothing regardless of whether the throttle is open or closed. Got dark and there's no room in the garage so I'll get back to it tomorrow after work hopefully. But i expected to get some sort of output and there was just nothing. I can't think of how it would end up causing a rich condition but cars are funky so whatever. Might be a winner.
Agouti
I'd plug your O2 sensor back in as not having that fitted is bound to muck up your mixtures with EFI.
serk
Does the ECU give you any codes?
Slowbrick
You have a vac leak. LH2.4 is very particular about these things. You mentioned you modded the cooler piping? Did you plumb the Idle air back in correctly. Does it hunt at idle? And does your speedo work?
Diverdonny
O2 sensor is fitted, working fine. Not sure how you got that impression haha but thanks for the reply. About to test the ECU when I get home. There's no lambda or CEL illuminated though. Idle air valve is correctly plumbed, but is receiving no change in voltage when i tested the throttle at open and closed. That's what led me to test the throttle position sensor which isn't responding when the throttle plate moved despite the audible "click" of it being depressed.
Diverdonny
When i say test the ECU I mean get codes from it
Philia_Bear
Diverdonny;81750 wroteO2 sensor is fitted, working fine. Not sure how you got that impression haha but thanks for the reply. About to test the ECU when I get home. There's no lambda or CEL illuminated though. Idle air valve is correctly plumbed, but is receiving no change in voltage when i tested the throttle at open and closed. That's what led me to test the throttle position sensor which isn't responding when the throttle plate moved despite the audible "click" of it being depressed.
Its a pwm motor
You wont see a voltage change
Philia_Bear
Lh2.4 hast a test mode you can activate via the diagnostic port
Including testing the idle air valve
Diverdonny
AH that was silly of me. I haven't got a logic probe handy so I'll have to work off my other findings which indicate it's okay anyway.
So I pulled the codes from the OBD module tonight (totally forgot about that capability, thanks mate) and got 223- IACV signal not present. Pulled the plug off it and tested the plug; got 12v with the ignition on. Pulled the IACV off, (very clean inside) and hooked it straight to the battery- and it opened up very strongly. Refitted to car, started it up then unplugged the IAC and it made no noticeable difference, surely some sort of hint but I'm not sure what exactly that would indicate.
I also unplugged and tested the TPS in various positions with the ignition on, which clicks right as the throttle plate opens, and got no voltage at the pins. I got very excited about this finding until I realised a few minutes ago that there most likely would be no power present if the plug wasn't inserted into the module. Can someone confirm this is correct and if I need to test the wires with the plug inserted, or have I found my gremlin?
I'm going to order a new distributor cap, rotor, leads and plugs since they're overdue anyway. Probably fire the parts cannon and see if I can do the intake manifold and throttle body gaskets this weekend as well just to rule them out and for a bit of fun since I don't think they've ever been replaced. Should I still be looking at the TPS as a possible cause here?
Angus242164
lol @ parts cannon, that's a good one.
Given that the idle motor tests OK, I think you have either a faulty TPS, or a wiring issue. An internal fault in the ECU is also possible, but less likely.
To go any further you really need a wiring diagram for the system, so that you know what to test for on the idle motor and TPS plugs. There should be something online, they are also in the Haynes manuals.
If LH2.4 is the same as earlier systems, the TPS will work by switching a wire from the ECU to ground, when the throttle plate is closed. If this is how it works, you should be able to short the two pins in the TPS plug together, to simulate the TPS contacts being closed, and the motor should operate.
The other pin on the TPS is a WOT contact, not normally used for anything in earlier models, I'm not sure if LH2.4 makes use of it. It's typically used for electric kickdown solenoids on auto's in other makes, that same TPS was used on heaps of makes and models.
Vee_Que
Fwiw, the car had all the vacuum hoses replaced when the intercooler and turbo was changed. Before, with the auto, the car would start then die straight away, but idle mostly fine when hot. Now, with no bov at all on a GT2871, I still think its the lack of bov that causes the stalling issue as all the hoses are now brand new and don't leak like the previous vacuum and intercooler piping as well as the intercooler end tank itself.
I did manage to have it not stall on me if I left my foot slightly on the throttle pulling up to a stop. The check valve for the brake booster is most likely knackered also, which won't help issues.