peinti

Hi, I have a 2000 LS400 Platinum Edition with roughly 121k miles on it. Recently, I did a major tune up that included valve cover and spark plug replacement. My mechanic cleaned the throttle body as well. He told me that one of the ignition coil boots had to be taped as it broke. It's a temporary fix that shouldn't affect anything.
The car is running really smooth as it should. However, when I sit at a red light in a stopped position (with foot on the brakes), the car is jerking in irregular intervals (every few seconds). It appears to be coming from the engine area. It's not a violent jerk - I am sure nobody from the outside would notice - but it is more than just vibrations. It's like the engine has hiccups. I can hear some faint, unrecognized sputtering noises related to it as well. It idles fine (RPM gauge doesn't change) nor do I have the check engine light on. It happens continuously at every light/stop sign.
My mechanic thinks that it is due to bad gas because it has been sitting for a bit over a week. I don't think it is related to gas though. It sat longer than that before without giving me any trouble.
I checked the transmission fluid. The color looks good and it is topped off.
Any idea what it could be? I have the feeling that something hasn't been connected properly.

timmy0tool

iTrader: (7)

sounds like slight misfiring however if there are no Check Engine Lights then it could be something else. does the car "hiccup" when the car is in park or neutral?

speaking of gas, are you putting premium octane (minimum 91)? not doing so will cause the engine to knock (but it should not be felt in the driver's seat).

peinti

Thanks for the response. I need to try out the same in park or neutral. I haven't done so yet.
Yes, I always use premium octane (91) only - usually Chevron or Shell unless it's unavailable. That shouldn't be the issue.

fixmiester

Might have arcing in one or more of the coil boots. ECU will not throw a code for arcing, because it sees that as a normal discharge of current. Might be able to hear it though. You can play with the boots while the engine is in drive, with parking brake on, or wheels chocked, because this will slightly load the engine, making misfires more noticeable. May have to loosen all the boots to troubleshoot, by twisting the coils and lifting each one to see if engine stumbles. Do not pull the boot out more than a half inch during this test.

peinti

Thanks, Fixmiester. That ended up being the issue. I had a damaged/worn boot. The issue went away once I replaced the boot. I ended up changing all eight.

YODAONE

What replacement boots did you use?

peinti

I bought them on Amazon. The brand is called Beck/Arnley. They're working fine. I no longer have any misfire issues.

Yamae

You mean this?

peinti

Yes correct

Yamae

Thanks for the confirmation, peinti.
Was the spark plug OK? I mean I have seen spark plugs were also damaged when boots were failed.
Attached photo below shows an example of a leak problem. The boot had a crack and the spark plug had black spots and lines of arc-trackings. Replacing the boot fixed the problem only for a while. The problem was started again and it was completely fixed after both the spark plug and the boot were replaced. Cracked boots often cause the damage at the insulator of the spark plug. I hope yours was OK.