Wonky idle and stumbling?

[GRSHOPR]

I was driving down the highway at about 60 mph, when I heard a sound almost like a pop, and then the engine started stumbling, running rough, and idling at about 1500 rpm, the idle switch will NOT turn on at idle, and the fuel trim jumps back and forth between normal (around 100) to crazy high (140-175), and back, randomly. I checked all the boost lines, everything checks out, so I figured the next option was the IAC.

I have the BlackStealth digital gauge installed, so I can check the IAC, and it was idling at 39 steps, and with the AC on, at 71 steps. So, naturally, I figured it was the issue. I just replaced the IAC, and pulled the battery to reset the fuel map and trims.

I warmed up the motor, everything looked great, the IAC even dropped to 0 steps, the engine idled at 800 rpm (which is about 50 higher than normal, but it was within range), the idle switch was on, and the fuel trim was right at about 100, fluctuating slightly. As soon as I put it in gear, it went right back to the same thing. What's the next step? I'm not sure what it could be next.

Also just confirmed that the throttle cable is the correct tautness. The O2 sensors are brand new, as are the spark plugs. Running out of possibilities.

Also noticed that when it was running rough, the O2 sensors were registering 0.01-0.03V and the TPS seems to fluctuate seemingly correctly. It randomly starts working correctly as well. Any suggestions?

[CoreyB]

Sounds like it could be the MAF. Does Not explain the "pop" you heard though.

[GRSHOPR]

Maybe the pop was a backfire? How can I test to see if its the MAF?

How's it going Corey! Long time!

[CoreyB]

I test it by unplugging it, if it runs better without it, the MAF is usually bad. A bad MAF will sometimes idle just fine but try to die as soon as a load is on the engine.

Things have been great, I am still around a lot, but I mostly just lurk these days. Things good with you, outside of the car problem?

[GRSHOPR]

Just busy as all hell with the car and school. Somehow, there are no TT front driver calipers anywhere in the US. Lol.

What have you been up to?

Oh, and ill check the maf tomorrow and report back. Thanks.

[CoreyB]

I just bought 2G TT calipers for my car, they were a pain to find. I can find plenty of 1G ones though.

[mb3000]

Pressure tested yet?

[GRSHOPR]

Just finished a pressure test, and it was perfect, save a BARELY leaky clutch boost line due to a crack on one end. Also, after I finished the pressure test, unplugged the MAF. It ran even rougher, and at lower rpm.

I was getting ready to adjust the BISS, since the idle was off due to it being moved (don't ask, it'll just be better), I happened to notice smoke coming from the engine bay, as I was about to ground the idle adjustment pin (the one in the brown plug), and looked at the source of the smoke, to find the coil pack exploding itself, much like those "snake" fireworks that you light, and they grow out, in columns from those little puck-like discs. Safe to assume that this was the issue?

[GRSHOPR]

Ok. Replaced the whole coil pack. It was still running rough, and the CEL was still on, and the tach and logger are still not reporting the same rpm. I took it around the block, just to test to see if there were more symptoms under load, and in that 2 minutes drive, it blew up another coil, the same one again (3/6). This time, on a hunch, a checked the temp on the coil, and it was burning hot, hence why it was spilling its guts.

I just checked timing. It's perfect. The ECU is immaculate. I'm thinking the ptu. Input from anyone?

[mb3000]

Symptoms of the PTU are generally that 3/6, so I would give that a shot.

Stealth 316 - Power Transistor Unit (http://www.stealth316.com/2-pwrtransunit.htm)

[GRSHOPR]

It occurred to me that the most common way to melt a transformer like that is a short. Sure enough, found a short in the harness, soldered it back up, and it's running strong and perfect again. All that crazy shit, and two coils later, and it was a short.

If anyone is having a repeated issue with their 3/6 coil pack, be sure to check out your engine harness.