sudden heavy plug foul and idle trouble

[sharpcadd]

have a '92 MX3, w/ a BPT swap. Has been running great for past 9 months since the build. Was running a little rich, but other than that no problems. Did not drive it for 2 weeks at Christmas, came back and ran great for a couple weeks.

All the sudden, one day I start getting a bit of plug foul, and the idle went way low (100rpm).

The next day, the car won't idle. It takes a bit of gas to get it started, and then have to keep foot on gas just to keep running at idle. The boost spikes right as you hit the throttle rather than taking a sec and smoothly spooling up.
Accelerating - car runs smooth, lots of HP
Decelerating (by compression) - car runs smooth
Steady throttle – bad plug foul
Car in Neutral and throttle up – bad plug foul.
Lots of smoke coming out the tail pipe, and turns the grass black behind me.
Fuel economy cut in half
Not burning or leaking oil at all
PCV valve had oil in its filter

Replaced spark plugs, wires, adjusted throttle body back and forth, idle pin, timing… nothing changes the condition. Replaced the PCV valve and filter.

What you think?

[SuperK]

I'm not familiar with turbo setups, so I can't offer advice whether the issue is linked to the setup or not.
However, if it was NA I would suggest the following:

O2 Sensors. They gotta be changed sometime!
Injectors.
Ignition. It's possible you're getting a weak spark.

But I'm not familiar with BP's or Turbo's, so whatever help that's worth. Hopefully someone with the same setup can help you better.

[sharpcadd]

I suspect it is not turbo related so I will try the O2 sensor next.

Turns out that it's not the boost that spikes right away, but the internal waste gate that opens too soon. As soon as I throttle up, the wastegate opens... I'm guessing this is a result, and not a caust of my problem though.

I'll let you know how the O2 sensor works out, and then I'll try the injectors.

[sharpcadd]

turns out that it is not the O2 sensor

[95 rs]

do you have a cat? if its plugged your car will run like a piece of shat. id try the cat if you have one. if not see if any of your injectors are stuck open or closed.

[sharpcadd]

I replaced a filter that I had on the pcv line. After a day of driving, it is clogged with oil. What does it mean if your pcv line is getting oil into it?

I pulled off the intake, and the throttle body has oil all over the inside. Is this the same problem?

[sharpcadd]

So it turns out that the problem was coming from the plug in the mass air valve... it was filled with water, and shorting it out. Dried it out, and all the problems went away.

[sharpcadd]

So it turns out not everything was fine and dandy. Took a long time, and many mechanics later to figure out that it was a simple as nothing was tuned right. I went through, re-cleaned the throttle body, re-set the throttle body according to the 4-cyl FAQ section of the forum, completely re-tuned the MAV, and put on a boost sensative fuel pressure regulator. This seems to have cleared it up even though I'm still adjusting the high end.

Long and short of it... heavy plug foul is a fuel-tuning issue. Can come from computer, mass air valve, throttle body, ground, injectors, cylinder temp meter (green plug), fuel pressure regulator, injector wiring, intake leaks... or in my case, all of the above.

Also, one mechanic wanted me to go invest in a stand-alone or piggy back fuel mgt system ($2500). Love my little car, but not worth that, and I know a lot of other people on here are the same way. Cost me nothing to fix this problem. Just a little patience, time, and TLC.

[Josh]

I know this is a little after the fact, but maybe if you asked the guy that built your car I would have told you right off. For starters, your car was never tuned right, you're lucky it lasted that long without proper tuning. You knew you needed a stand-alone or piggy back. Second, you spent thousands of dollars on all the things I told you not to buy. Maybe if you had actually treated me like the nice guy I was for storing your car for over a year in my garage, and the countless hours of free fab work i did, like an SS downpipe, SS exhaust, poly mounts-the list goes on. Oh, are you ever going to give back the 800 dollars worth of my parts off of my AWD car back? You kinda just stole them. Remember I was letting you borrow them untill you replaced them with your own.

Sorry for the flame guys, but this guy totally screwed me and there's several on the board that will vouch for it. He is the sole reason my AWD car has been off the road for nearly 2 years.

[sharpcadd]

2 sides to every story...

It actually ended up being the VAF. It just went bad. A new one fixed all the problems, and all the other things that seemed to work were only temp fixes.