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95 lexus sc300 idle issue

iwannadie

NAXJA Forum User
Location
Gilbert, Az
Ok 2018 has been rough on me. My xj threw a rode late in 2017 and now my backup commuter is down.

1995 lexus sc300 na auto 214,000 miles 🇯🇵

First sign of trouble was after about 30 minutes of freeway driving, I got off at my exit and the first redlight I had suddenly rough idle(rpm dropping) and it wanted to stall. I reved it above 1500/2000 rpm and it smoothed out and was fine the rest of my commute. It did the same thing on the way home only in reverse.
Next few days more of the same, revving to smooth out the idle worked and one day I had no problem at all after a quick blip of the throttle at a light. Today it was rough idle from the start and even noticed it while driving so it has gotten worse but not to the point I can’t replicate it. I get it home and the idle smooths out of course.

Yesterday it was running better than it had since this issue came about so I got on an open stretch and floored it. It did not feel right, it wasn’t making full power and kind of fluttering as if it wasn’t getting enough fuel at thr high rpm was my first thought. Fuel pump and filter are as far as I know factory originals.

I’m showing 14.xx volts at the battery while idleing with my multi meter. Battery has ranged from 11.98 to 12.5 with the car off on different days. That has me leaning towars alternator but never had one fail under these conditions. Also I replaced it with a new(not rebuild) bosch less than 10k miles ago. Battery is a yellow top optima less than a year old. I put the battery on my battery tender yesterday and showed full charge today(the worst day for this issue yet).
Serpentine belt is less than 2 months old.

Today at a light I noticed the engine was missing but the rpm stayed dead on and didn’t drop but a consistent miss happening. I am thinking fuel related.

I get gas at the same station, when the issue first happened I was at 1/4 tank and filled up. Haven’t noticed if a full tanks helps or not.

No codes showing. Plugs, wires, cap/rotor are about than 15k miles old. I am not in a position to dig into it to far as the xj is taking up my garage so compression test and all of that are just not on the table right now.

Thoughts?
 
I know nothing about this specific vehicle... but I'd throw a fuel pressure gauge on it to start. If it is stumbling at idle but smooths out when you open it up look at the Idle Air Control Valve? Probably can be cleaned up. Ditto the MAF, but read up on your specific model.
 
I was thinking IAC too but when it began to miss while actually driving I ruled that out in my mind.
 
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