supermj

Hi all,

Just hoping to get some advice. I recently purchased a 99 ls400 with 200000 miles. When I got the car, I had my mechanic install new plugs and plug boots and a new fuel filter. The car has been running great. A few hundred miles in, I got a check engine light. It was code 430. I had also had a day when I was driving it when it just randomly started running like crap. It felt like it was missing badly and even with a lot of gas, it barely pulled. It fixed itself a few miles later. My mechanic found that the exhaust was indeed leaking and fixed it. I picked the car up and it seemed to be running great. I drove it about 50 miles and 50 miles home and it ran like a top. I made a quick stop for about 15 minutes and then drove 5 miles. I stopped at a red light and when I started to go it was running like crap again. No check engine light. I went home and parked it. I got up the next day and it was running fine again. Still no check engine light and no other codes. Does anyone have any ideas on this. Obviously, it's very frustrating to not throw a code so we know where to look. Thanks in advance.

LScowboyLS

the most common cause of intermittent misfire and bad running with no codes is failing ECU capacitors

it's not the only possible cause, an electrical short or bad ground can also cause intermittent drivability problems as can many other causes such as a failing critical sensor in the fuel injection system or failing fuel pump, fuel pump relay, igniter or coil, but these kinds of issues will normally throw a code.