Looking for advice on an issue I have on my son's car. His car is a 1997 WRX with the auto trans. The problem is the engine will start and run but only at about 500rpm and appears to be over fuelling through the exhaust. I've pulled out the plugs and done a compression check (all around 125psi - cold) and all but #1 spark plug are very black with soot. Spark plugs and leads are new and double checked that all plugs are sparking whilst out. When the car starts and idles, we try and rev it up but it won't increase but we hear a lot of 'chatter' coming from the Idle Air Control Valve. I've tried another IACV unit but no change. We have also tried another MAF unit but this also made no change. The 'Check Engine' light goes out as soon as it's running and there is no codes in history. Any help would be much appreciated. Cheers

Would not be the oxygen sensor would it seeing as you have done the other two obvious ones.

Mark

Could be a faulty injector jammed open on the sooty cylinder or even a perished oring for that injector letting fuel bypass. Be careful with the over fueling that you dont wash the bearings with fuel contaminated oil it will fuck the motor.

The only reason I suspect this is I have had it happen before with a jammed injector. But it could still be something else.

What happens if you disconnect the idle control valve?

Thanks Mark. I haven't tried another O2 sensor yet, so we'll give that a shot. Cheers

You might be right about this. As it does seem to be fuel related but the soot is on 3 out of 4 plugs. We have since replaced the injectors but it now doesn't run at all. This could be down to using unknown secondhand ones but we will get the original ones cleaned and tested once I can find a place that is open during this holiday season. You make a good point about the over fuelling, as this engine sounded (when it was running) like it had a slight bottom end knock but I was hoping that this was down to it revving at only 500rpm. We can replace the block but would rather sort out this revving issue before swapping it out.

From memory, it did no change to it when we unplugged the IACV solenoid, other than bring on the Check Engine light. Why do you ask?

Hopefully could be just sounding like that,the knocking because of such low rpm idle. Only the reason I mention it I had a oxy sensor fail on another car and it ran like absolute crap not to expensive from memory, bit of a pain to get out due to being so old though.

Let us know how it goes Mark

usually a rattle at extremely low rpm is just gearbox noise (gear backlash).

Did you use new o-rings on the injectors? if the lower o-ring leaks it dumps raw fuel into the cylinders.

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Hopefully it works out mate hope the bottom end is ok


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I'm definitely going to try another oxy sensor, as we have a few to try but need to get these injectors sorted first, so we can at least get it running (albeit slow) again. I'll keep updating this post with things we try resolve this issue, as it may help others later.

How much backlash noise would you get in an auto? Same as a manual? But it definitely sounds like it was coming from under the manifold.

When we fitted the secondhand injectors, we used the old o-rings but this over fuelling (if this is what the problem is??) Was with the original injectors in it. I'd really like to get the original injectors serviced and fit back in with new seals and o-rings of course.

Do you know of anyone that can fully service these injectors? The place I use is closed for the holidays and hoping to get this done asap.

Yeah me too, as we have already had this engine out once no big worry if it does need changing, as my son wants to go 2.5 anyway but hoping to sort this revving issue first.

My other thoughts were TPS? But this seems like a bit of a PITA to get at. Anyone got a 1997 model that we can compare sensor readings off?

Cheers,
Paul

I didn't realise it was a slush box - they don't rattle.

What ECU is in this car? is it the original one?

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