cmack

Hi, first post here. Been reading for last week or so, trying to solve my car's problem. 1999 Lexus ES300. I bought this car with check engine light on and need some help. On cold start up, CEL immediately comes on and flashes. Codes are misfire on all cylinders. Car starts up and after a minute or two reaches a normal idle (800). Does not feel like it is misfiring at all, but check engine light is on and flashing. If I let the car warm up, half hour or so and clear the codes, the car will run and drive perfectly for 5-10 miles and then I will get a knock sensor code, but still drives fine. I have duplicated this sequence for 5 days in a row.
I have already replaced bank 1 sensor 2 O2 sensor and fixed a broken connection for that sensor. I have also replaced both Oil control valves with no change. I have seafoamed and filled tank with good gas. Plugs and coil packs are oem and look good. Everything looks good on "live data", no noticeable vacuum leaks. I have the new intake gasket set and knock sensor harness, but do not want to rip apart if I'm missing something else to try first. Can anybody point me in a direction of what to try next? Thanks in advance.

Nad1370

Seems like you have multiple things going.
Parts already been replaced to no avail.
If you can try to duplicate the check engine light again, pull up and see which code you actually have.
We'll start from there.
If there is a freeze frame when the DTC is set, let us know the data or take a pic of the freeze frame.

Richardsr

cmack

Thanks for the reply. I can easily repeat the misfire codes, as it does it every time after sitting overnight. The codes are the normal misfire codes for each cylinder, 6 total, both banks all cylinders. I can also take a pic of the freeze frame, but that will show the conditions at the exact moment of start for whichever cylinder fires first. I will try to post those tomorrow.
It starts and idles perfectly and once warm, no more CEL after I clear the codes, except for knock sensor code that comes after 5-10 miles. If I clear the codes before it has run long enough (half hour or so) the codes come back immediately. The weird thing is, I'm starting to believe the vehicle is not misfiring. I have access to a high end snap on scanner that shows the misfire counts on each cylinder and it reads zero on each cylinder while the check engine light is flashing and putting out misfire codes. Could a bad knock sensor or harness make the car think it is misfiring when it's actually not? Is possible for the car to throw a false misfire code? If this was your car, based on what I have told you, what would you look at next?

PFB

cmack

Thanks, I'll check the fuel pressure tomorrow

cmack

Thanks for the idea about voltage, I remember it being good on the live data, but I will certainly double check when I'm back at this tomorrow.

Oro

What do you mean by "good"? Remember, anything under 13 at idle is VERY BAD. Under 14 is NOT GOOD. You may know this, but some people think "12V system" means literally that at all times. It dos not.

Nad1370

I would agree with Rich's sugg. about checking fuel press. (Key-on first and see what build up pressure is and while at start-up and misfiring)
As well as checking voltage reading at start up - idling when it misfires.

One thing stood out for me.
"Happens every morning during cold start". (like sitting overnight, right?)
Misfire goes away once its warmed up.

Have you noticed the exhaust fumes if you smell anything peculiar?
Like a sweet smell or unburned fuel?

How is your coolant level in your reservoir?
Has it gone down since you purchased it?
What's the rpms at when misfire (engine light flashes) occur?

For information, when misfire occurs, ign timing gets retarded to suppress it.
You also mentioned you have a knock sensor code. (which bank or is it in both banks?)
A bad reading knock sensor will pull timing as well. <-- might create a misfire depending how far back timing gets pulled.

Having your high end scanner helps since you can see live data on almost all inputs to the ECM.

If this was my vehicle, I'd go do the above checks first and others that suggested.
I'd also replace the knock sensor(s)/ "Y" harness since we know it throws the code for it.
(really hard to diagnose this w/out proper equipment so i would just roll the dice on this) lol

vedimalik