pappabass

Yes, another rx300 missing. This one is different, runs perfect, than has a single miss, then runs perfect. But, when it is under a strain it misses more. Less noticeable when cold. Also when it runs without strain, you cant feel it. But no codes other than a sensor heater code. (Not a bad sensor, but the sensor heater)
Replaced the plugs, a few of the coils, cleaned IAC, oil has been changed every 3-4K,
If this was a car without a zillion sensors, I would say a fuel filter or fuel pump. My understanding there is a code for that, Any ideas ??

salimshah

Welcome to Club Lexus.

Can you please elaborate on "missing". Is it misfiring or stumbling (sudden drops in rpm). Misfiring is clearly due to no spark or wrong ignition timing. While the stumbling is typically due tp an issue with fuel Injectors/pump).

Does your CEL light up during self test ... Engine not running and when you turn your ignition from ACC to run (one position short of start).

Misfire should produce flashing CEL. Fuel delivery problem normally does not set the CEL.

Salim

fastnoypi

assuming the sensor heater is the one in the o2 sensor, it is a sign that the o2 sensor is going bad. Most manufacturers ecus will interpret by changing the fueling and cause a "rich" stumble by falling to its failsafe maps.

JAB

Whenever I have experienced what you describe the fix for me has been changing the air filter or the plug wires.

Drcoffee

Another hit and run newbie.

my guess would be a faulty fuel injector. Had something similar on a 4runner. Cold it would be fine but when it was hot, the injector coil would be intermittent. Mostly okay and then miss. Then it died and threw a code.

pappabass

Sorry for the delay in response. The engine runs smooth, then it has a 'single' miss. Like a nibble on a fishing line. Every 5 or so seconds. More often when hot. But when it is hot, it misses more when under a strain than when it is cool.

fastnoypi

How many miles do you have on the plugs? Just a possibility that the gap on one your plugs have widened or it might be a knock event with the ecu pulling timing.

pappabass

Probably no more than 15K miles. Gapped correct. I replaced the 3 coils that were on the back side. Checked the front side coils. IAC cleaned, unplugged the MAF & vehicle would not run, unplugged & reconnected some of the related connectors. Poured injector cleaner, premium gas, tailpipe appears a little lean. idles smooth when cold, accelerates fine, when hot & under a load, misses bad.

salimshah

I hope your plugs are OEm.

Salim

pappabass

I hope so, I need to verify, they are NGK which service manual says is OK

pappabass

[QUOTE=Drcoffee;9596064]Another hit and run newbie.
Sorry, I did not respond fast enough...

salimshah

We covered the basics here ... only odd statement was 'gapped properly' ,,, the irridums should not be tampered with, but if the gap was measured to be good but not altered we should be good.

Misfires are reported immediately by the ecu.
Does your CEL light come on during self test ,,, ignition key moved from ACC to RUN (step before start).

The only other thing would be to clean out the OCVs.

Salim

pappabass

Thanks for the advice I will research and clean the ocv's. I will also re-scan to verify no new codes. Here is something else. This may be related or unrelated. In the mornings when you unlock the doors from the inside, they snap like they supposed to. Then other times they barely unlock or won't unlock at all. You can hear them try to unlock but it just will not rotate far enough. The vehicle was doing this before it started running rough. Battery recently replaced no battery or charging alarm and check the grounds.

carguy07

What code is it showing?

pappabass

Ok, sorry for the delay, after cleaning MAF, IAC, PVC, OCV's & filters, ( which were actually pretty clean), bottles of fuel injector cleaner, checking many connections, scanning & only showing a sensor heater code, ( which does not affect operation after vehicle warms up) I took to have repaired. 2 things, 1st, one of the new coils had intermittent failure when it got hot. Would not show a code. Only found when tech used diagnostic tool going from coil to coil, 2nd, previous repair place installed wrong plugs several months ago. They were NGK, but the wrong ones. They physically matched, but the resistance was wrong. So, it runs good now. Good for 100K more miles! Well, after a timing belt !
Thanks for your advice,,