How bad could a duff water temp sensor make a car run?

V5 STI

Picked the car up (knowing it had a rough idle) yesterday and it did run lumpy at idle, it drove ok apart from a slight missfire at around 3krpm if you held it on light throttle. On WOT it seems ok (albeit a bit slow)

Thought it could be MAF, air leak etc so today been playing..

One thing though when the car is cold it runs really bad and the lumpy idle will go into a stall when cold, when it was warm yesterday it wouldn't stall at all.

Start it from cold and it runs A1, then literally 5 seconds later idle drops down low to stall, picks up a bit, then will go down and stall. Try and drive it cold and it's almost impossible to drive, you have to keep the revs up and slip the clutch.


Now things I've tried today..

MAF (put this MAF on my wagon to check on power FC and it reads 1030 so it seems good, plus it looks new) but also tried 2 other MAFs

Idle control valve (swapped with my wagon which is known good)

Removed bailey dumpvlave

o2 sensor (swapped with wagon, known good)


Fault codes only say idle control valve but I'm pretty sure it's only logging that because the idle is all over the place? plus I've tried a good one and no different.

Only thing I haven't tried is water temp sensor. If they go (looks original) do they make the car run really bad? I was hoping it was o2 as it's only really bad when the car is cold (hence why I'm now hoping water temp sensor)

Was hoping she'd be A1 today

 

When mine was going (93wrx) i got a dodgy idle, it would start go upto 1500 then down to 300ish then back up then back down.
Once warm perfectly fine.

 

Oh well, might try my wagon one on there today. May try my power FC on there first though.

 

I just put my power fc onto the type r to check the sensors..

The water temp sensor gives the same voltage as my wagon (ign off) and falls slowly as temp warms (like wagon) All the sensors give the same voltages.

Only thing that differs is with ign on (not running) the wagon has DEF and POG on and the type R doesn't.

I can't find anything on the net that tells me what these abreviations on the power FC hand commander mean though. Does anyone know?

Other thing I noted was the o2 sensor on the wagon (when ign on, car off) was 0.002v and when running at idle was a steady 0.9v. The type R was 0.02v and 0.8v (and fluctuating when running) and if I held the throttle at 2krm it goes down to 0.00v.

I did try the o2 sensor from the wagon on there yesterday but no change.

I started the car this morning and it ran perfectly for around 20secs then it starts to mess around, rev it a bit and it'll then drop idle low, bog and stall.

 

jollygreenmonster will know the abbr as he maps them (ww.jollygreenmonster.co.uk)
have you looked for any physical problems (holes in hoses etc)?

 

Mines the same replaced Maf Throttle sensor Idle valve and its still playing up Help

 

I gave up searching the net and have now to remove the inlet manifold, going to check all pipes and hoses and it may well be an inlet manifold gasket leak.. give me a chance to get the inlet painted anyway.

 

Can you keep us imformed if you fix it plz Bella x

 

mate i ran a thread on this just a few days ago i had same problem did error codes and nothing but jollygreenmonster and a few others advised coolant temp sensor i have brought one brand new for only 21.00 pound ....i also reset ecu first and for the time being this as settled down so dont know if temp sensor would have cured it yet, just leavin it a while however its a very easy job . id go for it ...good luck

 

Thing is I've checked the voltage back to the ECU from the water temp sensor and it's the same as my other Impreza. The voltage also falls as the water heats (as it should)

The car is really undriveable when cold, I put it in the garage earlier and it took a fair while just moving it. You have to keep the revs right up and it won't move unless you really rev it.


I've removed the inlet manifold and haven't found andy split hoses. The inlet gaskets were a bit snarled up and one had sort of swollen where water from a leak from the header tank had been 'working' on it but to be honest I've seen worse. I had inlet manifold gasket leak years ago and it made the idle really up and down IIRC.

I'm frozen through after today, been out there busting my back over it in the cold.

 

I'm now wondering if it may be a lack of fuel on a more mechanical level. (ie pump knackered)

It's just strange how it runs A1 as you fire it up, then will start to die.. but then again when I bought the car (and it was warmed up) it ran ok, apart from a slightly poor idle.

 

sorry i carnt help any futher mate so a free bump to top ....try jollygreenmonster

 

If your getting an error code for the idle air solenoid and you have changed it for a known good one, check the voltage to it, i cant remember which pin it is, might be the middle one, or the two outer ones. you should have min of 10v to it with the ignition on. mine ran badly until i discovered the main relay has fried, leaving all the sensors without power, and the only code i got was the idle air solenoid.

 

I'll check when it's back together.

Anyone else got anything else I should check while it's in bits?.

 

ive got them same problem mate only mine was real bad went southend lastnight and pulled into sealife center went for a jimmy started it back up wouldnt rev above 2500rpm and stunk of petrol spitting spluttering dont know what it is

also noticed that on the air/fuel gauge throughout the night it was getting richer and richer as it normally runs lean all the time but now when started straight on lean

 

right thats wierd started the car this morning and i drove up the road gave it a blast and its running much better only its still hesitating around the 2rpm mark as i have no idea why this happened lastnight im now taking the car of the road untill i can find out the reasons why ;-(

 

Please tell us what you find.

My 06 STi is also doing it and I wondered if it is just because it is super-cold at the moment - fuel too cold?? Starts, runs for 5 secs then dies. Blip the throttle and it holds - idle it a while and it seems ok. Very wierd...
I wondered if it is the Ambient Air Temp sensor? I have done nothing to the car, still trying to figure it. I reset the ECU (I am still not sure this is possible with my model - conflicting posts on this)

 

...Other thing I noted was the o2 sensor on the wagon (when ign on, car off) was 0.002v and when running at idle was a steady 0.9v.
Faulty sensor

The type R was 0.02v and 0.8v (and fluctuating when running)...
Correctly working sensor

 

Right,put it back together today.

Things I've this morning before start up.

Checked all boost hoses
Checked all breathers
Checked inlet hose (samco anyway)


Things I've replaced before start up this morning

New inlet manifold gaskets
New spark plugs
New fuel filter


Things I've tried off my wagon previously.

o2 sensor
MAF sensor
ECU (power FC)
IACV

Now since doing the above and getting it all back together today I started it up in the garage and it sounded good, drove out, all ok.. hmm.. then after a bit it started messing and died.

At this point I decided to fit a new spare 255l fuel pump I had laying around. When I changed the fuel filter I tipped the filter up and the fuel looked very dirty.

After I fitted this the car would idle without dying off and I plugged my Power FC and checked the water temp voltages and readings (both looked normal) and checked the MAF voltage again (looked good, 1030 engine off ign on)

Car still runs rough, if you try and drive it, it's now driveable when cold but holds back and doesn't like it when you try and accelerate.

When warm I actually drove off and got some fuel, behaved well coming to a stop etc but just drives bad, holds back, and missfires at specific points in the rev range.

Only thing I am yet to replace/change is the water temp sensor but as I'm getting good voltage (ie 4v dropping as it warms) and 'expected' temp readings on PFC monitor then should I bother?

I'm pretty sure the fuel pump and filter wasn't helping as the car seems better than before and was actually driveable when cold (whereas the other day I could hardly move it)


I'm tempted to try the MAF and o2 sensor swap now it's running better as it may well have been a combination of a lot of things, I've certainly illiminated a fair few things but just don't know where to go now!

 

I used to have really crap running from cold... would start ok then would idle abit funny as it warmed up. Once warmed up fully was ok.

This got worse, it was still starting fine but the idle from cold was alot more lumpy and mis-firing. Once warmed was ok.

First thought was basics... so changed the spark plugs and everything is absoloutly fine now and feels like it has gathered some of its power back, alot of its power back infact... makes the clutch slip in 3rd sometimes now though ahh well its going off the road soon!

Dont know if this is the same as what your getting but thought I'd mention it... I was always told when your plugs are on the way out on an Impreza you'll get a miss-fire on boost but I didnt get that.

Gaz

 

Main culprits IMHO are water temp sensor and MAF. Seeing as the former is less than £30, then I'd buy and fit one of those first.

Also, MAFs for your model are 'only' <£80 (unlike early ones @ £260 odd ).

 

I just fitted my new MAF from my wagon and took it out from cold (I'd let it warm yesterday)

It drove poor from cold and I got to a junction (about 400 yds) and it died and didn't want to start. Tried to restart it and it didn't want to fire, sounded strange, like no fuel.

Sat for 5 mins chatting to a passing neighbour and it fired up after this time.

I've ordered the water temp sensor now.

I did consider dirty injectors but i'm not sure it'd act like this.

Only thing is the water temp sensor acts as it should (regards voltage) and looks new..

Whatever it is it's worse the colder it is, the other day I tried to drive it straight off from cold and it was minus 1 ambient, it literally wouldn't move from cold. Today it's warmer and would drive much better but still died. Once it's warmed a bit though it is driveable but with a bit of a lumpy idle.

 

Possibly a loose plug on an injector?

Banny

 

they all plugged nicely and inlet's been off and on so I've unplugged and plugged them.

I'm not holding my breath with water temp sensor so when that doesn't work I'll scrap the bloody thing!

 

Water temp sensor fitted and no change!

Started up from cold (after fitting new sensor) running A1 (as usual).... then 20secs later, it feels like the fuel gets pulled and it dies. It won't restart straight away, leave it 2 mins and then try and it fires up, won't want to idle though and misses, keep the revs up to 2krpm (and all the time it's fighting against you to die) and once it gets a bit of heat into it'll idle. Take it for a drive and it won't accelerate, drives fine until about 2,500rpm and then bogs and feels really flat and lumpy if you try and accelerate.

One thing, when you try and restart it after it's died for the 1st time (and it doesn't want to re-start it sounds really strange, like it turns over differently, don't know if it's because no fuel is going in or something but it sounds different when it turns over and it only sounds like this at this time. When you start it 1st thing it sounds normal and when it's warm the cranking sounds normal.

I tried to unplug the injectors when it was running but can only get to 2 when it's running and both times it ran worse when removed. I had a good listen round each injector and can't hear/see any leaks or anything. I tried to remove 1 of the injectors but it was really in there tight so gave up.


The best bit is the guy I bought it off now admits to knowing all this despite him telling me it was fine and just needed 1 HT lead as his mechanic told him it was fubbered.

Anyone want a project Type R

Only other thing to note is the is the knock sensor has been replaced and the plug is missing off the cars loom and someone has put a spade connector on it and plugged it into the knock sensor plug, only 1 wire. But I'm sure a knock sensor won't make the car behave this way anyway..


Time for a few of these as I'm out of ideas and fed up..

 

sent PM on 22b

 

Could it be the valve clearances set too tight?