Weird throttle-related thing -

[Marky]

Got a BH the other day, seems 100% good, but after a while noticed when driving the revs seem to "hang" for a second when you let off, it's like a half a second delay between my foot and the motor. Same if changing gear or just backing off to coast/engine brake.

It has since developed a bad idle - ok ish when cold but deteriorates to stall/1500/stall/1500, and if you breathe on the pedal it jumps to about 2k. Stopping at the lights you're fine for about 5 seconds as it stabilises, then it begins to oscillate and get to the point of stalling again, before catching and revving up again.

The cable itself is fine, moves freely and isn't over or under tightened.

I have replaced the IACV outright, and notice a definate difference in idle with it unplugged - so I can assume that's out of the equation.

Driving around the car is 100% perfect, drives smooth, boosts normally etc. Will run through some AFM cleaner anyway but it just seems too severe for it to be that?

I can't for the life of me find anything online to help but maybe someone here knows what to check for? Can I just fiddle with it till it seems good or is there a certain resistance or voltage I should set it to when closed/open?

Any help is very mucho appreciated

[clintondane]

Sounds a lot like what happened with our Blitzen, turned out to be the O2 sensor. Might be wrong, but can't hurt to check.

[subieboy]

Use some CRC556 or Rostoff on the throttle body where the cable/spring/etc meets and give it a clean

Worked reasonably well with mine a few years ago

[rex-leggy]

 clintondane said:

Sounds a lot like what happened with our Blitzen, turned out to be the O2 sensor. Might be wrong, but can't hurt to check.

+1 very similar symptoms on my bg also

[Marky]

Ok... multimeter to see if o2 voltage is swinging back & forth at idle to diagnose then?

Will check fault codes tomorrow, it's driving me mental as the car is perfect otherwise - got the feeling the guy I bought it off barely used it, and its just bad luck I've given it a decent run which has nuked something in the meantime.

[Marky]

Ok - no fault codes come up

Cold start it is perfectly smooth, only as it warms up idle starts to deteriorate.

The only thing I'm now stuck with, is there's a solenoid tucked between the intake and the alternator, has a hose in from intake mani, and it goes out to ??? underneath the manifold.

That had cracked, I have blanked off both hoses in the meantime till I find another one (of whatever it is?), what does it do, where does that hose go and could it be related to this poor idle?

[resurrection.inc]

Yes vac solunoid ring submurine spears in chch. Mine broke they really hard to get piping off with out snapping them use a razor if need be. They charged me $50 it did the same to my car with idle but not as bad. Def check o2 though.

[Guest]

If its what I think it is it goes to the carbon canister just throw it out and bung the mani vacuum source.

[Marky]

Appears all of the above might be right

TPS is adjusted right

AFM clean as a whistle

New IACV and has had seafoam through the intake

Had intercooler etc off, found a couple small issues but nothing terminal or at least nothing which would explain the idle

02 sensor appears to be stuck on 0.1V, heater works - the other wire doesn't

Trying a second hand one today - see what happens

[Guest]

AFM can still not work even if its clean...see if you can borrow one to try. O2 sensors do wear out and should be replaced at least with cam belt if you dont know when it was done chances are it hasnt.

Are you the marky off msport?

[Marky]

Not entirely sure the 02 I got even works haha, might have bought a dud as it's made the barest hint of a difference. Taking it to a subaru guy down here tomorrow to chuck diagnostic / logger thingy on it to see what it says, I'm tearing my hair out trying to figure it out and don't have time to mix and match parts stabbing in the dark. Figure he'll have a spare AFM to test with as well, like you said it might still have been the fault all along.

Did find a split in the WG hose while I had everything apart, explains why it felt so healthy!

And yeah that's me, traded diamonds for stars - wife won't accept any more mongrel VR4's in the driveway!

[Guest]

Is msport dead now? stopped checking in as it seemed full of spam and cant find it or google it either now. Did you have the write up on fitting GTO front brakes to VR4?

If you unplug afm does it effect the car? likewise with o2?

[Marky]

Sort of - all the guys who started it have drifted away, and to be fair the guy who runs the website keeps forgetting to renew it hahaha. The brakes from memory was literally just making a dog-bone to space them out a bit and bolting them on!

I haven't tried unplugging the AFM while idling - good idea, will try later on. The 02 there is absolutely no difference with it plugged in or not, I am thinking it's likely the fault but I think I just need to get it diagnosed properly before I go spending $$ replacing things - any other car this would be pretty straightforward to sort, but these subies just seem so fragile with sensors etc it's easy to chase your tail.

[Guest]

Ha makes sense. Yea the name rung a bell.

Not as bad as GDI though...loving subarus now but all that early evo stuff is pretty basic. Someone can correct but isnt o2 just for closed loop?

[Marky]

Stupid car

Went to see Stu at Stubaru, he just said "afm" when I pulled up and I'm all "but surely it could be these other things the interwebs told me... I GOOGLED DAMMIT"

No, replace AFM, car runs sweet.

My 02 was borked also, and the TPS was slightly out of adjustment, but neither had an effect on idle, however the car at least now has a clean bill of health?

Painful part was after whipping AFM out of it's housing and giving a blow out, it seemed to run OK - this is AFTER I forked out for a brand new replacement @ armstrongs. No matter, will leave old one in garage for when this one nukes itself too.

My understanding with the 02 is it is ignored when car is cold, and on heavy throttle, but is used at idle / cruise. If you listen to a car idling you'll hear it ever so slightly changing in pitch up & down as it swings rich:lean:rich.