Hi. I have just bought my first Scooby, a 95 WRX Jap import. I don't know a large amount of technical info about Impreza's so please excuse my lack of knowledge and the lengthy post. I just want to know if a rough idle is normal?

The car has a lumpy idle, she seems to 'cough' every few secs or so, but the timing of the coughs are very irregular. There's no regular 'rhythm' to it, just random 'coughing'. She drives totally fine and there are no other problems with her, no chugging, stalling or anything else while driving, just a rough idle. I bought the car from an extremely reputable mods garage - the best in NI - and they assured me that a rough idle is normal in a car like this. However, I just wanted to check as I don't want to ignore a possible problem.

I couldn't tell you exactly what mods are in the car, just all the usual. She did 279bhp on a rolling road, if that gives you any idea of what the mods may be. I do have a list of them, but haven't got it with me at the min. I get about 200miles from a full tank, just thought I'd throw that in as I've no idea if that is good or bad - the cost isn't an issue. She had a full service and all the mods done 7mths ago - approx 4000miles - at the same place I bought her from. Every mod has been done to the highest spec.

Any thoughts on this would be greatly appreciated. Lisa

 

On start up (from cold) my car (93wrx) revs quite high then settles around the 800/900rpm mark.
When mine had a rough idle problem on it was the coolant temp switch (but that does normally switch the engine fans on).

 

Shouldn't have a rough idle. Lots do, but shouldn't have. 200 miles from a tank is not a lot unless you're absolutely hammering around everywhere. Idle control valve is probably to blame but at almost £300 new from Subaru it's not a cheap fix. Try a scrappies.

TBH you'd be best to get it into a decent garage with a rolling road and spending the money you don't mind forking out on bad fuel economy, on an expert looking over it and tuning it so it works properly.

 

Thanks for the advice. I'm not totally ripping it everywhere. Just driving the same speed I did with my old car - this one just happens to have faster acceleration.
I didn't think that 200 miles was a lot from a tank, but, never having had a car like this, I thought it was perhaps normal. I'll def get it into a garage, as if it's not right I want it fixed. I don't want to do any damage to it and I want it running the best possible with good performance. Cheers.

 

What dump valve is fitted, original?

 

When I had this Lambda sensor was to blame.

Once a new one was in the idle was spot on and the fuel consumption got better.

 

The dump valve in the car is the one that was put in with all the other mods 7 mths ago. As far as I'm aware there was no other dump valve in the car.

 

Is there any way to check if the lambda sensor is at fault or do I just have to replace it and see? How much would that cost?

 

Do a search on here for how to check for fault codes.

There are wires to connect under the steering column that will display fault codes through the check engine light.

 

Scoobypedia | Trusted knowledge for everything Subaru | Scoobypedia browse look under ECU

 

It may need adjusting again. If the spring has become a little weaker now it has been run in this will cause a bad idle with little other problems. If the DV is an adjustable type there will a small nut on the top. If so try winding it in by a full turn, if this cures the prob or improves it you will then need it setting properly.

 

Should the engine warning light not be on then?

 

When i had an idle problem my CEL didn't come on (93 wrx) but the sensor was faulty.

 

A friend who is a mechanic said that, if it is the lambda sensor, cleaning it sometimes can help. He is gonna try that on Wednesday to see if it makes a difference.

 

Cleaning it can work but often doesn't. Idle problems can be caused by any number of different things, but there is only ONE component that governs idle at the end of the day - the idle control valve. If it's not running weird in any other way, I'd suspect the most obvious cause first. It's just very expensive to replace it unless you can get one from a scrappies.

 

Just thought I'd give it a go. There's a scrappers near me with about 10 totaled scoobies so could go there. How difficult are they to get out. Would I be able to remove it myself from scrapyard? Do you have any idea how much it would cost to get it fitted, (excluding price of part)?

 

Is it difficult to remove and replace idle control valve? I can't find anywhere online to tell me how to do it. I've got a idle control valve lined up. Its costing me a tenner so not too bad. Just trying to see if I could get my hubby to do it as he's an engineer. I've noticed when people ask where the idle control valve is and how to remove it, no-one answers them. Does that mean that nobody knows cause it's really awkward?

 

No it's because everyone seems to mess about with the MAF sensor, the coolant sensor, this sensor, that sensor. In fact every electrical component in the engine bay apart from the idle valve. It's actually very easy to deal with and you've done well to get one for a tenner. I'd say it's half an hour's work for hubby with some half decent tools. Assuming you know which part it is. The following is the order I did it on my v4 WRX which has the idle valve next to the throttle body and close to the intercooler as well.

1. Remove intercooler
2. Pull off rubber air hose and disconnect electrical plug from idle valve
3. Pull off two small rubber water hoses at the bottom, one each side. There will be a little water spilt but not much.
4. Undo the 4 bolts that hold the valve onto the inlet manifold.
5. That's it. Refitting is reverse of removal. Before fitting your new one, give it a good wiggle and blast it out with carb spray.

Lastly, once the new valve is on, the engine may run much worse for a few minutes, it needs time to get used to running with a working valve. Also the two screws on the top which you can loosen to allow the electrical top part to swivel, are for adjusting idle speed. Normally this doesn't need to be touched, but if you find your idle is much lower or higher than normal (should be 700-800rpm) then swivel this one way or the other to get the idle right.

Hope this helps.

 

Even though the ISCV sets the makes the engine tick over at xxx rpm, its told by the ecu inn the first instance,which gathers its data from sensors around the engine, You could have a small air leak which would seem fine other than at idle speed.

 

Yes of course the ECU is in charge; the idle valve has an electromagnet in the top that cycles the duty valve back and forth and according to the speed of this cycling, alters airflow through the valve.

 

Guess what? It's fixed. I tried putting octane boost in with the petrol and it cured rough idle and I get more out of tank. I put ultimate unleaded in the car but the highest octane you can get in NI is 97 octane, whereas the car was built to run on jap 101 octane, so when I put octane boost in it took petrol up to 100 octane and it idles brilliantly. Cheers for all your help guys.
Lisa x

 

Glad it's sorted.