Random engine missing...BAD!

[a_scayola]

Hi everybody!! The car in question is a stock 1990 Legacy L Wagon with 120k miles. I just got the car last month and the only thing I've replaced besides fluids and the radiator, has been the purge soleniod valve.
The CEL doesn't go on at all now.
There is absolutely no pattern as when its gonna start missing. It's a really bad idling going up and down to 600 rpm and even stalling sometimes. There's black smoke and the engine vibrates like crazy. Complete loss of power up to 1500 rpm where it will still miss a little. But then most of the time it will run perfectly fine even though I dont feel its making the power it should (of course I got the car like this so I dont really know) and the gas mileage sucks (15 MPG).
It's going in for a tuneup asap, but I thought I'd ask the experts first!
Any suggestions???
Thanks!

Andres
90 Legacy L Wagon
Miami, Fl.

[ciper]

Multiple issues most likely.

The changing idle speed is usually a dirty IAC. Search for that term to find a cleaning procedure.

I bet the car only shakes at idle sometimes when its warm, if you let it sit overnight and start it in the morning it does do it right?

[a_scayola]

The engine runs ok when cold.
Also, when its running rough there's a weird smell....hard to describe, but it's not gas... it's kind of acid..

I did search for the IAC valve on this bbs but I couldnt find a description or a picture of it. I did find the cleaning procedure though. I only need to find it the IAC now!!

Thanks
Andres

[entirelyturbo]

1) It sounds like a bad MAF sensor to me. Your plugs are probably fouled beyond belief with carbon deposits from way too much fuel. That's why your mileage is bad. When the MAF goes bad, it defaults to a very rich setting. Hence the black smoke, poor running etc.

2) If you searched for "IAC", I do hope you found my posts about it! It is a very delicate procedure, and I would recommend using brake cleaner instead of carb cleaner. I had the misfortune of seizing my IAC and ruining the $360 part. The IAC valve is located under your PCV valve, find the first vacuum hose on your intake hose following your MAF, that leads to your IAC valve.

[IggDawg]

check your coilpack for cracks. if the problem ges worse when it's humid, it could very well be the coilpack. unbolt it fromthe intake manifold and inspect the underside and around the base for any cracking.

[a_scayola]

Would a bad MAF sensor give a code? Because I'm not getting any right now.
Thank you all for the help!!
Andres

90 Legacy Wagon
Miami, Fl

[entirelyturbo]

There are distinct advantages and disadvantages to OBD1 and OBD2 ECU systems. OBD1 (which is ours) we can read ourselves, but it's not very sensitive or conclusive. OBD2 must be checked with a scantool, but it gives a much more accurate solution to the problem.

That said, it's very possible your MAF could be biting the dust without throwing a code....