I just read your post and you are correct. I made the same mistake and had the same results. It's was the MMO.Greetings all! I apologize for the long post. I'm hoping someone can give me some direction. Hours and hours of googling and reading through forums like this one have given me a lot of possible things to look at, but no real firm starting point.
I have a 2005 ZX3 SES I bought earlier this year. It ran great for about a week, then threw a CEL and started stalling out every time I let off the gas to come to a stop. I replaced the plugs. I cleaned the throttle body (sticky and gummed up) and the IAC valve. I would have replaced the air filter but it has a lifetime filter and the indicator is well within the green range. The car stopped stalling, but instead started idling high, 2000-2500 rpms. DTC said minor vacuum leak, so I pulled the intake manifold and cleaned the flaps, cleaned inside the block where the valves are, cleaned the TMAP sensor, replaced the pcv valve and tubing (which had a huge gash in it). In order to get the intake manifold off, I had to remove the fuel rail. One fuel injector came out with it, the other three stayed in the engine block. I replaced the affected o-rings. Put it all back together and it ran like a top.
I had read some good reviews online about Marvel Mystery Oil and since I could tell this baby hadn't received much love, I thought it would be a good idea to clean the fuel system. I read that MMO could be used in the fuel tank or during an oil change which I thought odd but figured it must be ok. What I DIDN'T read were the instructions, instead assuming it was like all other fuel treatment products I'd used, and dumped all 32oz in at the next fill up. Basically 6-8 times what I should have put in. About 90 miles of driving later, it started coughing and sputtering and shaking like it was going to fall apart. There was also an occasional loud "pop" coming from just behind the engine. When I pulled over, the engine compartment smelled like when you burn the ends of a polyester cord to melt them a bit so they won't fray. The serpentine belt had been shaken half off the pulleys and I had to pry at it to reseat it. I sat there and spent a few hours reading online, determined it must have been the overdose of MMO that caused my current woes. The consensus was that I should drain the fuel tank and put in fresh gas. I also read that the catalytic converter can be damaged if the car is driven while misfiring, so I got roadside assistance to tow me to my storage unit where I spent the night waiting for them to open so I could get my tools. Next morning I couldn't get my siphon hose to reach the fuel through the filler hose, so I drained the tank by connecting my siphon hose to the fuel line in the engine compartment, disconnecting the battery negative terminal, shorting the fuel relay, turning on the ignition key, then making contact with the negative cable about 500 times to get all the fuel pumped out. I also replaced my serpentine belt since the old one had sustained damage. I then put in 5 gallons of fresh gas, and many cranks later got the car started. Again, rough idle, sputtering, coughing, popping. And my serpentine belt fell off. (Over the course of this ordeal I've had to put it back on 3 times, and reseat it by prying at it 3 times. I'm assuming it's the roughness that jostles it off since when I'm careful to not let it run too rough it stays on.) I read a ton of stuff about what all this could mean, thought maybe I'd damaged fuel injectors, fouled valves or plugs, fouled oxygen sensors, ruined my catalytic converter. A friend suggested there still might be MMO in the system, advised putting in Chevron supreme with techron and a fuel injector cleaner, then drive it until the catalytic converter gets hot. So I did that. Drove it for 150 miles with only a couple of stops. Mostly on freeway with some in town traffic. And it only runs marginally better. It doesn't pop, or maybe I just turn it off before it has a chance to. I noticed that sometimes after I start it it'll rev up to 3000 rpms and stay there for a bit before settling down to cough, sputter, and shake. I don't know if that was happening before I drained the fuel, so I'm worried I damaged something draining the way I did. Also, as long as I was cruising 60-70 mph, it seemed to run smooth, though it lacked a little power. If I let off the gas and coast, occasionally it will keep accelerating, and I imagine that if I had it in neutral at those times it would be revving up to 3000 rpms on its own. Otherwise when I let off the gas half the time it'll surge and cough, the other half nothing. If I then apply the accelerator slightly, say to keep it at 45-55 on level highway, it bucks and surges. Once it's under a load and picking up speed it settles down. When it town, it coughs and surges most of the time, but occasionally settles down and runs normally. But very infrequently. Now the DTCs it's throwing are:
P0171 system too lean (bank 1)
P2195 O2 sensor signal stuck lean bank 1 sensor 1
P0128 coolant thermostat (coolant temp below thermostat regulating temperature)
P0420 catalyst system efficiency below threshold (bank 1)
So now I'm wondering if putting in too much MMO was just a coincidence, or maybe all this really was caused by the overdose.
If caused by the overdose, things I'm looking at include damaged/fouled or leaking fuel injectors, damaged fuel rail pressure sensor, damaged or fouled plugs, damaged or fouled O2 sensors, damaged or fouled catalytic converter, and gunk that's been loosened up and is now wreaking havoc. Also possible collateral damage if by draining the fuel as I did I either stressed the fuel rail pressure sensor or fuel pump too much, or confused the crap out of the PCM/ECU.
If a coincidence, I'm looking at all the above plus possibly the MAF sensor.
All hoses seem tight and well-attached. I pulled the vacuum tube off of the FRP sensor and the end of it did not smell like gas.
Does anyone have any ideas about what's going on? Am I missing anything? Any suggestions of what to try first? Second? Etc?
And what do you think of Scotty Kilmer's suggestion to clean the catalytic converter by putting in a gallon of lacquer thinner when the tank's half full and then running it at high speed for 150 miles?
Thank you so, so much, to anyone who chooses to give me some considered, pertinent advice!
I should also add that my car has the same hard to start issue that so many others have. So I'm familiar with what my fuel pump sounds like. And it seems to me that after draining my tank as I did, the pump doesn't run for as long as it used to when I turn the ignition to "on".
Also, when I say it settles down once it's under a load and picking up speed, that's only when I'm giving it quite a bit of gas. If I'm accelerating moderately, or slowly, it bucks and surges.
Just finished driving it across town. It's definitely backfiring. Not many loud pops from the engine compartment, but the exhaust is noisy like it has an exhaust leak, only it's not steady, it surges.
I sure hope someone here can help me!