tylojuky

My 16-year old son purchased a 1994 ES300 with 161,000 miles - his first car - it's what he could afford

When we first looked at the car, it had the following codes:
P0135 - O2 sensor heater circuit (Bank 1 / Sensor 1)
P0300 - Random Misfire
P0301 - Cylinder 1 misfire
P0303 - Cylinder 3 misfire
P0305 - Cylinder 5 misfire
However, the car ran as smooth as silk and replacing an O2 sensor (even Bank 1) isn't a big deal. So we bought the car and drove it home (over 100 miles) - it ran like a dream the whole way home. I erased the codes. P0135 showed up again almost immediately but that was the only code.
My son drove it to school 3-4 days. It ran great / no issues whatsoever. Meanwhile, I ordered an O2 sensor and we're waiting for it to arrive by mail.

2 days ago, at a stop sign, the engine ran rough / CEL blinked. Press on the gas and it smooths out and runs fine. Engine smoothed out and it drove smooth the rest of the day - only that one event at the stop sign. All three Bank 1 misfire codes are back.
Yesterday, same symptoms - only at idle - same misfire codes - but it happened 3-4 times instead of just once like the day before (it's becoming more frequent).
Today, the misfires are much worse and they don't get better. Now we have a new code (P0330 - Knock Sensor 2 circuit - Bank 2). At this point, it just barely starts (limped home), if you give it any gas, it dies, white smoke from the tailpipe.

I don't believe in coincidences so it's hard to believe 3 coils in the same bank and a knock sensor all went bad at the same time.
My first thought when we got misfires on all 3 cylinders on bank 1 was a timing belt (jumped a cog on the bank 1 cam shaft) but the misfires smoothed out when you open the throttle and went away for a day. So now I'm doubting the timing belt fixed itself then went bad again.
The white smoke has me concerned - could this be a head gasket? Is there a way I can diagnose this without throwing money at it or tearing the engine down? Would a head gasket cause intermittent misfires on one bank that preceded it getting worse?

Any advice would be appreciated.

Thanks

tylojuky

Here's an update on the symptoms:
- No noticeable white smoke anymore - that only happened once
- No milky substance on the oil filler cap
- No noticeable coolant loss
- When I start the car, it will idle smoothly for quite a while, then misfire/chug/almost die, then smooth out again.
- While idling smoothly, if you touch the gas pedal, it chugs and will die if you don't let off. If you let off, it idles smoothly again - will keep idling smoothly for a long time.
- You can't get enough power out of it to move from its own shadow. If you put it in gear and touch the gas, it dies.

Now I'm thinking
- maybe not a head gasket unless it JUST happened all at once and there hasn't been enough time for any coolant to leak / burn out
- Weird that it will idle smoothly then randomly misfire, then idle smoothly (unless you press on the gas)

It was a cheap car but it was nearly all my son could save mowing lawns so it's a lot of money to him. We don't want to throw parts or money at it so looking for advice on how to diagnose what's truly wrong before spending anything.

Could this all be tied to a faulty O2 sensor? I'm going to replace that anyway since I got the bad heater circuit code but I'm wondering if we just replace that only and see what happens?

Any advice on what else we can look at while we're waiting for the O2 sensor to be delivered?

Thanks

mmatheny

Doesn't that year have only 3 coils with the back 3 cylinders getting a plug wire from the front coils? If so, maybe the coil wires are bad.

tylojuky

I don't recall off hand (can't see bank 1 under the intake plenum). I'll find out this weekend when we start looking into it.
I do know 1994 was the first year model with the 1MZ engine (in the US).

It seems unlikely to me that all three plug wires (or coils) would go bad at the same time. Stranger things have happened - I'll post back when I have an answer.

tylojuky

Here's what I know so far (working on it today finally).
It sat for a couple days un-driven & un-started. Now it won't idle like I posted above (the engine was hot when I did that test, now it's cold).
Today, it takes a little extra cranking to get it to start but it'll start and run smoothly for about 2-3 seconds, then sputter and die. Pressing the accelerator only makes it sputter and die sooner. Feathering the throttle (like in the old carburetor days when an accelerator pump was bad) does not help - it just dies.

I replaced the O2 sensor in bank 1 (one of the codes above) but that did not "fix it" (I doubted it would but I knew that sensor was bad & needed replacing anyway)

This engine has 6 coils (not 3 coils & 3 wires like the 1993 model).

I got the intake plenum off so I now have access to Bank 1. While I was at it, I took my time and checked every ground wire, every vacuum hose, every electrical plug. Nothing obvious / nothing loose / no dry or cracked hoses or anything like that. Everything that I took off seems to be in good working order.

The inside of the intake plenum and the top of the intake manifold are very dirty with a burnt-oily film. I don't know if that's normal after 161,000 miles or not (is it?)

I tested the spark on all 6 cylinders / coils. All tested fine. There is no discernible difference between bank 1 & bank 2 coils but I might swap them anyway when I put it back together.

My next step is to test compression to completely rule out the head gasket. Assuming it has good compression and it has spark, then I will test the fuel filter & full pump pressure.

Please post any advice or suggestions you might have.

Thanks,

tylojuky

Update:

- All 6 cylinders produce 190-200 psi on a compression gauge and hold it for several minutes (less than 5 psi bleed down). With this result, I will consider the head gasket intact - please, can someone confirm that for me?

I replaced the spark plugs just because I had the plenum off and access to bank 1. I also swapped bank 1 coils for those in bank 2 (no real reason - just did).

I wanted to do a fuel pressure test but I don't have the gauge and renting one would be $150 (nearly the price of a fuel pump). After thinking about it more, I would think that a low fuel pressure issue would present itself in either random cylinders or all cylinders. However, the only time I get a misfire it's always cylinders 1, 3, and 5. Never any other cylinders, never just 1 or 2 cylinders (always those three at the same time). Consequently, I have temporarily ruled out a fuel pressure issue. Same reasoning tells me it's probably not a MAF sensor issue.
Can someone please confirm or argue with my logic on this?

I put it all back together (had to replace a PCV valve that I broke) and no love. Still won't start. If it does try to start, it just dies immediately.

One thing I noticed when trying to start it was that I occasionally got a muffled "whoosh" when I stopped cranking - like a backfire inside the intake. The only time I've ever seen that is when there was a timing issue. What I don't know is if the "electronic" timing on this engine can get that far off or if it could only be "mechanical" timing (i.e. cam shaft slipped a cog).
My next step will be to check the timing belt. Does anyone agree or disagree that a timing belt issue could present intermittent misfires on bank 1 (3-5 different times over 2 days) and then get worse (no start)?

Any help or advise would be much appreciated - pleeeeeeeease!!??

tylojuky

Update:
I took the timing cover off and rotated the craft to TDC. Here are some photos and some questions for you experts out there who've done this before.

First the crank:
It's a little hard to see but the white mark on the pulley is lined up with ZERO on the black plastic ruler
Is this correct? Or should it be lined up with 5-10 degrees????
Now the front cam (bank 2):
This looks pretty close to me. If it was off one tooth either way, it would be further from the reference mark than it is here. Remember I never got a code for misfires on bank 2 so this is what I would have expected - right?

Now the back cam (bank 1).
I couldn't get the camera perfectly lined up on this one so it looks further off than it really is. If I was able to move the camera to the left a little so I was in line with the cam shaft, it would be nearly dead on with the reference notch in the back cover.

So - I don't think I have a timing belt problem - does anyone disagree?? I'm really desperate for help here.

What should I check next?

Please help.

mmatheny

Man I wish I knew - you're going through a bunch of troubleshooting! Hang in there, there are GREAT mechanics on this forum.

tylojuky

Thanks for the thoughts, mmatheny.
I've sense spoken to a Toyota master mechanic with, long-term experience with Toyota/Scion/Lexus. He said a few things that ring true:

• "If a whole bank misfires, it's almost always the O2 sensor (A/F sensor on newer cars). Nothing else makes sense. I can't ever remember a time it was anything but the O2 sensor or A/F sensor."
• "Always replace the O2 sensors with OE (Denso) sensors. The other brands have faster or slower response time than Denso. Toyota computers are expecting the response time of a Denso."
• "It's a good idea to replace both upstream O2 sensors at the same time because they change with age."
• "Fuel delivery (pressure or filter) problems will give random misfires and a few other codes you're not getting - same for a MAF sensor issue"
• "The misfires left unburned fuel in the exhaust. As much as the car has been cranked and as many misfires as it's had, the O2 sensors are now having to deal with that mess in the exhaust stream which will only make it harder to find the right A/F mix."

Based on his advice, I put the car back together and reset the fuel trim values. I disconnected the new bank 1 O2 sensor (this one is a Walker, not a Denso) and tried starting the car. A disconnected O2 sensor will cause the computer to default the fuel trim to a fixed value. I tried & tried and finally got it to idle for a little while - now I have a little hope.
I then reconnected that Walker O2 sensor on bank 1 and tried again - finally I got it running good enough to drive it. The more i drove it, the better it got (unburned fuel in the exhaust stream getting cleaned out - also this is the source of the white smoke). It hesitates and runs pretty rough but it's drivable.
When I read the live data using a scan tool, I can see the values of both upstream O2 sensors changing but they're not in sync. They're never perfectly aligned but they should follow the same "curve". These two don't - they're just "off". When one goes up the other goes down and vice versa - they're not responding at the same speed. At this point, I think the ECM is hunting for the right air/fuel mix and it's a constant battle between the two banks - this is complicated by having a single down-stream sensor on this vehicle so the result of both banks' fuel trim is measured by one sensor after the cat (instead of one for each bank). I have 3 new Denso O2 sensors on order and I intend to replace them all, reset the fuel trim again, and start over.

At this point, I'm just really relieved (1) I don't have a blown head gasket and (2) the timing belt is in good shape. Any other repairs will be cheaper than either of those two.

tony2000LE

Try replacing the MAF sensor if it is still running rough at an idle. The majority of the issues your having, I did also on my 2000 es300. Here is a link to my thread, and hope you get it sorted out. T

https://www.clublexus.com/forums/es-...eshooting.html