Hi. I just picked up a 1993 SC400 last Friday - 133K miles, very good condition, drove great. I was very excited to find such a nice example.

Well, Friday night, when I was leaving a friends house (after I only had it for a few hours), it was really down on power. I noticed the idle was rough and the exhaust note sounded like I was running on less than half of its cylinders. It's like someone swapped a 3-cylinder Fiesta engine in place of the V8, then removed a spark plug. It must have taken at least 30 seconds to accelerate from a stop to 60. The problem occurs at all RPMs - it's similar to an engine that's "missing"

The problem right when when I started it up and it's been that way since then. A few hours before it was running as smooth as could be.

Do you have any ideas on what I should look for? Could it be a vacuum leak, bad airflow sensor, something wrong with timing or ignition? I did search, but did not come up with any good results. If you have any ideas or could point me in the right direction, I'd greatly appreciate it.

 

Update

I took it to a shop near my home today. The mechanic observed some oil smoke (which I did not see before). He did not really look in the engine, but said the valve cover gasket is leaking onto the exhaust manifold. He said I'll need to do a "complete tune-up" which will run $1200. I've replaced this gasket on my other cars - it took less than 30 minutes on a 4-cylinder Honda and less than two hours on my Acura (NSX with has a very tight engine compartment).

So, I asked how much to just replace the valve cover gasket - he insisted that it'd take about the same amount of labor since there's so much stuff to remove. Eh, I didn't get a good vibe from the mechanic - so I left.

New Questions

• Could a leaking valve cover gasket cause this type of problem?
• I'm not sure if it's actually leaking - could the smoke be from crankcase ventilation hose that broke?

Again, any ideas would be very welcome. Thanks guys and gals.

 

What is the condiction of the PCV? If malfunctioning, pressure builds up in the engine and oil seeps from the valve covers and valve guides. This is a common cause neglected at times.

 

what's your oil consumption like? when was the last time you changed your rotor/cap/plugs? timing belt? all of those things could cause misfiring

 

Resolution

Tammy and Durrr, thanks for the tips. The good news is, thanks to the recommendation of a fellow Club Lexus member, we got it all fixed it. The wire that runs to one of the distributors was frayed (due to improperly installed cover) and shorting. It was insulation burning that the first mechanic ID'd as smoke from oil leak. I actually thought it did not smell like oil (I remember a distinct "electrical" smell), but figured that surely mechanic knew better than me. At least I trusted my instincts and did not left the car with the thief.

Thanks again.