Hello, I recently bought a 1993 Lexus SC400 and I’ve been having some issues with the idle and overall performance. First, I replaced the spark plugs with NGKs, then I replaced the spark plug wires with NGK wires as well. After that, I drove it for a couple of days and noticed that after the car sat for a while, it would have longer crank times before starting. It always started eventually and never stalled, though. It doesn’t blow black or white smoke, i have driven it about 200 miles since i have owned it for a bout a week.

I also occasionally experienced high idle around 1500–2000 RPM. When that happened, I could shut the car off, wait a few seconds, restart it, and the idle would return to normal and the car would drive fine.

This morning, I noticed the idle acting up again, so I gently tapped on the IACV. After that, it seemed like the IACV may have closed because the exhaust sounded like the engine was starving for air. I ended up taking my Jeep to work and left the Lexus sitting for about 9 hours.

When I came home and started it again, the exhaust sounded better, but there was a strong smell of gas. I also noticed that when pressing the gas pedal in park, the RPM would rise to about 1500, then suddenly drop, sometimes almost to 0 RPM, although the engine never completely died.

I’m not sure what’s causing the issue. Any ideas?

 

I would guess the two things are unrelated.

I chased long crank starting problems for a long time in my first SC, and it ended up being a loose connection on the return line at the fuel tank, as I recall.

RPM issues around 1500-2000 suggests coils are failing. That's the exact range I would expect. Although, the symptoms don't quite match what I've seen in that respect.

I would also be suspicious of the ECU, if you don't know that it's been serviced.