Cleaned Engine, Now Running Rough

[greenphant]

I did an oil change on my C280 yesterday and then cleaned the engine with degreaser/hose as directed on spray bottle. Ever since, the car has been idling very rough, especially when it's stopped while in gear. I don't think I got water into any of the electrical systems, and I drove the car for about 120 miles since cleaning the engine, so I would think that would work out whatever might be wrong, but no.

Anyone have any ideas? I was thinking about replacing the ignition wires to start with.

The strange part is that it idles very rough, but the tachometer is steady, no hesitation there (which reminds me of the bad motor mounts in my old 190E)...

Thanks,
G

[Proven Guilty]

the pre-update C280s had an infamous bad wiring harness, and the engine bath could have triggered the inevitable.

however, simply check your vacuum lines. it's the easiest thing to do when you first notice a rough idle without smoke coming out the tail pipe.

[greenphant]

Originally posted by Proven Guilty
the pre-update C280s had an infamous bad wiring harness, and the engine bath could have triggered the inevitable.

Oh man, I pray that that is not the problem.. I'm quite aware of that issue. I didn't use a pressure washer or anything like that, just a hose without a nozzle, no harsh spraying, and I covered up the fuse box, etc. with plastic.

What would be some other symptoms of the harness going bad?

Any tips or links on checking out the vacuum lines?

[strictlyspeakin]

Is it possible that any water got in by the spark plug wires?

[DynoXG]

Yeah, I agree, check the spark plugs first. If you have time, remove them and leave the hood open to allow everything to dry.

[greenphant]

I'll check out the plugs soon. I also realized (which just came to me when I was kicking myself about the whole situation) - I got gas (at a no-name station) just before doing the oil change/engine wash and it wasn't running funny right after that, but took a couple starts. Maybe a case of bad gas? I'm going to run some drygas and injector cleaner tonight - I won't be able to get to the plugs til later this week...

Thx guys!
-G

[Will_w202]

It's almost certainly the plug wires. if they're over 5 years old or original, they are suspect. You will get misfires and throw a CEL eventually. Change them before you get stranded in a rainstorm (like I did)

[OzC36]

Did you fill up the spark plug wells in the engine head with water?

[Python01]

A couple weeks ago I did the same to my old lady, 89 MR2...

After cleaning the engine, the car could hardly idle and just kept dying. With horrible misfiring, the engine sounded and smelled like a dirt bike.

Then when I pulled out the spark wires and looked inside, I found the plugs were DEEP IN THE WATER!!! Wonder it ever started at all!!!
Engine came back to normal condition after all the water was drained and dried... (it took me a while though).

So, the bottom line is, check yours too

[greenphant]

I checked them out and it was all bone dry in there. It seems like on the 280 that the whole spark plug compartment is pretty well sealed in there.
I am almost 100% sure it was just a case of bad gas - since I filled up at a cheap no name place right before all this - it just seemed weird cause it all happened at once. I ran 2 cans of drygas and 1 fuel injector cleaner through it and now (knocs wood) it's finally running normally again.
Thanks for all the tips!
-G