Just had a new STI block fitted to my car & both me & my mechanic are stumped on this one. It starts fine, runs fine but exactly 5 minutes 7 seconds after starting the engine revs keep dropping & rising agin. Turn it off & start it again & it's fine but once again 5 minutes 7 seconds later the idle keeps fluctuating

Anyone have any ideas as there are no fault codes whatsoever & the MAF & Lambda have been checked. The water temp sensor is new, as is the crank position sensor so we're a bit confused?

Any help would be appreciated

Cheers

MAFFA

 

Tried another ECU ???

Idle Control Valve anything to do with it ???

stabbing in the dark here.

 

Air leak somehwere that only happens once it gets warm?

 

dont know if its a standard timing thing, but is it when it switches from closed/open loop that the lambda isnt working or something like that?
or when it goes through transition (open/closed) the voltage accross the MAF?
as above, stabbin blindly here

 

its sound like a case of the maf symptoms are you definatly sure the maf is ok?

 

If you unplug the MAF, it should stall straightaway. Not a guarantee check, unless you fit a new one to test the theory.

Stefan

 

Dont know if this is true in all cases but, was told that the ECU uses a pre set air ratio setting before switching to the MAF sensor readings.

So maybe the ECU is running the engine then when it switches over the MAF is knackered.

Just a suggestion.

 

Just been to the garage to check for myself exactly what the symptoms are & i've gotta say i'm a bit stumped.

It doesn't actually hunt on idle. What happens is its atarts fine, ticks over fine & when you give it some throttle it revs fine. After between 5m 7s & 5m 15s it still ticks over perfectly but if you give it a small bit of throttle & hold it the revs keep rising & falling . Kind of like a nova boy at the traffic lights revving his engine.

Now i've never come across anything like this before but from what io've seen here the general consensus is the MAF....possibly. It's a shame the girlfriends hasn't got one otherwise i'd borrow it .

The idea of the hose being split could also be a possibility if the revving wasn't so strange. My mechanic is going to try it from cold tomorrow & see if it makes a difference but please keep the suggestions coming as i'll take this thread with me to give us a few ideas

Cheers

MAFFA

 

had this rising falling issue on mine.
no idea what it was, but it did it after you left it idling when got home etc.
basicly - to cut a long story short, i replaced the throttle body. Now i expect it was more an issue with the TPS , but whole thing was easier. the old one worked fine, and so did the new one, but with the new one on, it didnt do it. solved !

weird EH !
so - MY95 ecu . but STI block. changed anything else ? like the manifold / throttle body? etc?

too much chrome getting in the way?

check the TPS it may have been disturbed & causing the issue.
i couldnt work out why the hell it did it, as it made no sence...but there yah go, electronics for yah !

Steve

 

maffa

It sounds like the throttle position sensor or the maf you sure all plugs are conected properly what a bout fuel


Checked the fuel filter etc how is the lambda reacting

May be another ECU reset to see if the prob gets worse

 

I think that checking the MAF & TPS are the two points of call firstly. I can check the Lambda tomorrow. I guess the Lambda link won't work if it's knackered?

ECU reset is another option I spose but as the battery has been disconnected for this long I think it would have reset itself anyway.

Mmmmm a few avenues to take tomorrow God knows where i'll find a MAF though as the other scoob doesn't have one?

MAFFA

 

Steve,

The only thing that has changed other than the block is that the Inlet has been polished but that's it

MAFFA

 

MAF normally shows itself a few seconds after starting

check neutral position sensor too.

 

oh, and check TPS 'idle' switch too

 

Now, is the new STi motor / block compatible with the wiring for the '95 car ... i.e. is the car's wiring loom OK with the different engine block, where most of the sensors sit?

Who did the engine fit, did they just swap like for like ( assuming your's wasn;t already a STi ! ) or did they know what else to change ....


Call APi for more info if still stuck, they know what they are on about!
(Assuming it wasn't done there!! - well even if it was they will help!!)

 

It is all compatable as it was only the short block. All of the MY95 ancillaries are on it so yes the loom, fuel rails, sensors etc...are all still compatable. Would have been a different story trying to fit a complete engine.

MAFFA

 

Did the MY95 have a switch on the TPS?

Take it off and test it with a multimeter, or plug into it to get the volts and make sure its linear. It does sound like its wandering low down in its range.

Lambdalink will just be very lethargic if its the o2 thats shot. They tend to hang around at a low voltage (ECU thinks its running lean so puts more fuel in)

This is one where some plug in diagnostics would be good (SECS etc)

MB

 

we have full sensor readouts/logging from software a few of us wrote. its no secret how to talk to the early ECU's
Early (phase1) engines had a switch combined within the TPS that was for idle.
from Phase 1.5 onwards they dropped it. (not sure on buy/blobeye tho ? )

Steve

 

Thanks a lot for all this info guys. My mechanic should hopefully be able to test a few things with all this info

MAFFA

 

it sounds like a few possible common things:

Idle control valve is stuck, and idle is too fast, so ECU fuel cuts when over about 1500rpm making it go up and down.

TPS is in wrong position, and needs rotating to put the idle switch in the correct position

Lambda sensor is fubar, unplug and see if it still happens.

Engine will run with MAF unplugged, but will run on a limp home fuel map which is generally quite rich.

PAul

 

Cheers Paul

MAFFA

 

Pavlo, you just saved me a typing exercise. The above is exactly what I was going to say to the letter. Idle control valve is my first choice too.

We did build the short motor but it isn't going to have any effect upon what is happening here.

David APi Engines / APi Impreza

 

If it is the ISCV (and I think it probably is) then it can be usually fixed by removing the OSCV 'lid' (light brown thing held on by 2 philips screws) and checking to see if the the magnetic post underneath rotates freely. IF not, some light taps with a hard faced hammer will usually free it up.

Paul

 

Thanks a lot guys. Sounds like that could be the problem. I've only just picked this up so i've left a message with the garage to check that one & to check the magnet on the ICV. We checked the TPS today & it made no difference (even when we took the one from the other scoob). The only time it made a difference was when you disconnected it with the clip & then it was fine. A bit bizarre but there you go

Cheers

MAFFA

 

If you disconnect the TPS the ECU doesn't know that the car is supposed to be idling or on overun, so it will not cut the fuel as the engine goes past the RPM threshold.

Sounds just like your ISCV is stuck

 

Make sure you note the position of the sensor in relation to the retaining bolts, as that will adjust the idle if you dont replace it in the same position...

MB

 

How about the water temp sensor?

 

WTS is new & working fine. I think I pointed that out at the start of this thread...or was it another one???....So many problems, so little time

It turned out to be the TPS in the end. Got the multimeter on it and made a few adjustments & it ran fine .

I've just done 900 miles in a weekend & for some reason the idle is a little bit lumpy (for want of a better word) now? It ticks over at around 1000rpm when warm but just kind of stutters a little. There's a fair bit of engine wobble when it does it.

I think this is a case of things "loosening up" with the engine and a few adjustments now need making with the ICV & TPS to correct it? Possibility....or is my technical "know nothing" knowledge run away with me again? Multimeter to the rescue or something else?

MAFFA

 

ECU reset and see how it adjusts then. i imagine it was over / under compensating something else to allow for the TPS being out.

MB

 

I have this same problem but I have a Ver6 STi swaped into a 98RS with a PowerFC. So ther is no limp mode. I recently bought a new Idle Control Valve. hope it works cuz I can't return it....