Hope someone out there can help.

Just bought myself an Impreza Sport, 1999 with 64,000 on the clock. I'm delighted with it, but for two things (I've started a thread for each to keep track of things!). I've got a 3 month warranty from the dealer so keen to find out what's wrong.

For this thread, my problem is a lurching effect the car has when driving at steady low speeds (say 30mph). When I lift off the accelerator to adjust speed the car lurches a bit, as if it's been caught from behind. It's a bit like when you're trying to keep a steady speed when driving any car really slowly in traffic in 1st gear - you know that shudder. Only it happens in this car at speeds up to about 40.

When the car is cold, it's fine, and drives smoothly. I can only think that this maybe bacause the idle speed is kept high by the auto-choke. Perhaps this means that when I back off the accelerator the idle rev speed helps to smooth the ride, so to speak? So doea my idle speed need adjusted up. (The rpm at idle when the engine is cold is about 900 rpm and when engine is warm is about 3/400rpm.)

Has anyone got any ideas - maybe it's a transmission thing? Or maybe I need to adjust idle speed, or the throttle position sensor, but, honestly, I've no idea! Just guessing. Just hope someone out there can help - it's infuriating!

 

Gavin
Do you have an air idle valve on your car by any chance?

Kev

 

I've no idea! How could I find out?

 

First of all I think you stated that when cold your revs are at 900rpm, then when the car is warm it goes down to 400rpm,
I would say your warm revs should be 900rpm, 400 seems very low to me.

Secondly can I just check your symtoms, does your car say, when you are driving along at about 30 or 40 mph, feel as if its running out of petrol for a split second, so you push the acelerator pedal a little more to sort of get through the hesitation, then of course when it catches your doing 60mph ???????

I don't know if you have an air idle valve on a sport, but I'm sure if you do a search on her you'll find out, if you have and its a similar valve to my WRX then I can probably tell you why this is happening.
Kev.

 

Hi Kev,

Yes, symptoms just as you said, but the ''out of petrol" feeling only comes when I'm very slightly backing off the accelerator (to control speed), possibly to the point where I'm actually not giving it any gas at all.

Is this the air idle valve?

http://forums.nasioc.com/forums/showthread.php?t=781242

Gav

 

That doesn't look like mine on my car, but if that looks similar on yours then yes thats is the air idle valve, mine is as you look in the engine bay to the right handside of the manifold, it has a beige looking top where the wires come out of.
But as stated earlier you have a different car.

I believe my air idle valve is knackered, when my car is idling sometimes it hunts, say 900 down to 600, but what I think is happening, when you pull away the shutter inside should slide across cutting off the air idle valve and your engine takes over, however I think the sliding shutter on mine is not closing.
This could be a faulty part or the signal is not being sent to my ecu, so I am getting extra air into my manifold from the valve when I shouldn't be, so my mixtures are completely buggered causing my jerkiness/hesitation.
But when I get above 40mph and when I use a bit of boost I don't get the hesitation anywhere near as bad, I think the petrol is increased to balance it out a little,
Anyway I have bought a new one (old one was ten years old afterall) so i will let you know if this was the cause of my jerkiness, because believe me I have changed everything else

Kev.

 

Sounds like you've been through the wars trying to fix yours. Great advise, and am keen to hear if your replacement valve sorts out the problem for you. Thanks, Gav

 

Hi Kev,

Just wondering if you've changed your idle valve and if so did you get any benefit?

I cleaned out my idle valve + o-ring and it did improve things, but the problem is still there. I think I need a new valve and the Subaru garage say it'll be £216 or something ridiculous! They ( A.F.Noble in Penicuik ) were useless trying to find the problem, btw, it's crazy that a numpty like me can find it and an authorised dealer can't.

Cheers,

Gav

 

Gav,
I did buy a new one, £240 later
I think the price you have quoted maybe before vat?
Or maybe I'm just paying Southern prices
My jerkiness has gone now below 40mph, so I can only assume it must have been this.
If you do get a new one, you will need to reset your idle, by adjusting the two screws at the top (if its similar to mine)
If you don't know what your doing, then I'm sure someone on Scoobynet living nearby would help out. Remember it needs to be around the 800 to 900 rpm, as you stated before I think 400 is way too low.

My second problem that I had was jerkiness and knocklink activity at high speed, around the three figure mark (when on track...cough..)
I have since found out my HKS dumpvalve was leaking..........unable to hold back 1.4 bar of boost on my 2.5 lump at the top end of the car, I have since bought a Forge with stronger internals and the problem again is sorted, I have no idea if my HKS leaking may have been a factor in the other jerkiness, but I doubt it.If you have a dump valve have a close look at it
Anyway hope this helps
Kev

 

Update:

I've changed the throttle position sensor. No change.

Cleaned the AICV - slight improvement (it was filthy in there).

Tried to replace the AICV but wrong one sent by HDC Subaru - hope replacement due soon.

Throttle cable doesn't seem to be sticking.

Reset the engine management control after every tinker.

 

Right, a hell of a lot poorer but my car problems are gone!

Took the car in for a complete service, due to the vague service history I asked Ian Grieve Subaru in Falkirk to do a 60,000 service (plugs, diff, air filter, gearbox oil, engine oil etc), and check the cam belt while they were at it.

Turns out the oil that came out the engine, diff, gearbox, was disgusting. So sounds like my problem might have been there somewhere. Turns out it was a good move asking them to check my cam belt 'cause the guys who changed it last time (same folk who sold me the car) had left a piece of moulding touching the belt and it was slowly wearing into it...eeks. So cam belt changed as well.

Now the car drives so, so, so much smoother, it's amazing! I am, for the first time in 3 months, enjoying driving it.

Thanks for everyones help. It's a shame I never pinpointed the actual problem area (I guess engine or diff oil), but just glad to have the problem gone!

Gone for a drive....