1998 ES300 297,000 miles.

Engine has been having issues intermittently since December 2019. First it was having issues starting on about 3 separate occasions over the course of 3 months during the winter. Engine was cranking but not starting. 2 out of 3 times it started by modulating the gas pedal. 3rd time it took multiple days for it to start. Haven’t had starting issues since February.

Now this summer the engine started to run very poorly on cold starts and feels like a misfire, especially when I put it in gear (RPM below 1000).

It will also started to surge when cruising on the highway in top gear. Only way to get it to stop is to let go of the gas pedal and let it coast for a moment before reapplying the gas.

I got a flashing CEL for a Cylinder 5 misfire one day after a cold start while driving at about 40MPH. That gave me a clue to check my Fuel Trim with Live Data using BlueDriver.

I was able to confirm that my Bank 1 fuel trim spikes rapidly when the engine is surging on the highway and then it goes back to normal when I let go of the gas. I saw very high values for a split moment.

Bank 1 Short Term -25%
Bank 1 Long Term 50%

I know this is pointing me towards issue with Bank 1 where Cylinder 5 is located but I don’t know what it actually could mean.

Is there other Live Data that I should monitor to get a complete picture?

I replaced my spark plugs and fuel filter a year ago. I wonder if I messed something up that started to cause all these issues. During the winter I tried spraying some carb cleaning into the IACV and cleaning the throttle body but it didn’t help.

 

What about coils and especially spark plug wires? The wires going to the rear bank tend to fail eventually.

 

I replaced the cables in 2011 when I got the car with 173k miles. My engine has 3 coils on Bank 2 in the front and 3 wires going to the rear Bank 1.

Do you think a loose wire/connection could cause such behavior?

 

Are you sure the wires are good? What brand? Also check each injector connector (pull out and inspect). Could also be a bad ignition coil.

 

Ok I will do that. I also found another DTC in the system

 

yes, like Lexus2000 said, likely a coil. At that mileage, not unexpected. if you have to go in there for that, then change them all back there and new iridium plugs. As an economy measure, I have used low-mile take-off genuine coils with great success over the years, and also Autolite iridium plugs on this engine. And of course, pcv valve back there.

 

So I’ve been driving the car more often and monitoring the Fuel Trim, Engine Coolant Temp, and O2 voltage.

I know very little in this field, but I noticed my Fuel Trim numbers hover around 7-10% in total per bank. Today it was in the high 60s F outside and I noticed my coolant temp was at 165-167F on the highway with the AC off. Then while I was idling after a long drive with outside temperature at 65F, the ECT went up as high as 198F and then leveled off around 190F.

My thermostat is original, radiator was replaced two years ago, coolant is fresh. Haven’t checked if both fans work, I know at least one works when the AC is on. But what is the normal operating temperature? It feels like 167 is too low for highway driving and 198 is too high for idling. I was thinking 170-185 is ideal.

O2 sensor on Bank 2 was replaced in 2014 with a Denso 234-9009. Bank 1 received the same sensor in 2012.

I would expect good Fuel Trim values to be below 5% per bank. I believe 20% is when the computer sets a code. Maybe the O2 sensors are to blame? Especially with that DTC for Bank 1 P1133 (slow response from O2 sensor).

Reason I bring all of this up is because my fuel economy has been very poor as well. I’ve been averaging 20MPG per tank since April and I try to take it out on the highway for about 60-70% of the driving.

Maybe there is unmetered air coming in as well?

I guess I have to start with a good through inspection. Check all spark plugs, the wires, listen for hissing sounds? Check both fans.

I’m also thinking of installing a new thermostat when I do the timing belt/WP.

Last but not least, my AC compressor has been making a racket on cold starts and the pulley is visibly shaking when it’s engaged. Maybe that’s also putting a drag on the engine?

 

You probably need a new thermostat the OEM ones go bad eventually and do exactly what you are noticing, the engine temps drop during high speed driving. This is because the 'stat is designed to fail in the open position to prevent overheating.

 

What’s strange is it doesn’t seem to be stuck open, because the engine comes up to temp rather quickly after a cold start.

We had similar outside temp today at 65-67F.

Cruising on the highway with ECT at 167 or 171F, without or with A/C respectively.

Idling at 192-199F after a 40min drive.

Both cooling fans kick on and off automatically. I noticed they kicked on when it got to 199F. Didn’t matter if the A/C was on or off.

Coolant is at the right level, didn’t see any leaks.

Today I had the same misfire feeling on the highway. Observed the Bank 1 Fuel Trim reach 19.5% Short Term and 52.3% Long Term at its higher point, while going about 75MPH uphill. Once I slowed down and let it coast, it went back to normal again.

Here is a screenshot of that moment.





This article explains High Fuel Trim numbers

https://www.autoserviceprofessional....t-work-for-you

Possible causes:

• Unmeasured air is reaching the combustion chambers.
• Less than the commanded amount of fuel is reaching the combustion chambers.
• One or more sensors is reporting incorrectly.

and it recommends to check fuel trim for “at least 30 seconds at three different engine speeds: idle, 1,500 rpm and 2,500 rpm.”

My issues seems to happen at low idle speeds and under load around 2500-3000RPM.


“Low fuel delivery will cause an increase in LTFT as the PCM tries to compensate for extra oxygen in the exhaust stream. Remember, the PCM doesn’t measure fuel flow; it only knows injector pulse width and assumes fuel delivery is correct as commanded. Is equivalence ratio changing, too? If you add propane and see LTFT and equivalence ratio numbers come down, there probably is a fuel delivery problem. If there’s no change, an oxygen sensor may be faulty or shorted to ground. Don’t forget to check this at different speeds and loads, because fuel flow problems often don’t show up at idle.”

Maybe I have an injector issue? I’m thinking if it was a fuel pressure or fuel flow problem with the pump it would show on both cylinder banks and not just Bank 1.

Another possibility is a bad O2 sensor for Bank 1 or an exhaust leak at the Bank 1 exhaust manifold letting in oxygen before the sensor.

 

High speed driving means way more cooling, if the 'stat is lazy it will cause your temperature issue. Maybe your thermostat isn't bad but it sounds exactly like what I've seen many times.

 

That makes sense, I will definitely replace it in the near future. What’s crazy is the temp gauge is in the middle even when ECT is at 199F. It has such a wide range for “normal”.

 

I think Lexus2000 is right; I've seen that a few times, too.

The lower-dollar stant, etc. thermostats are extremely flimsy compared to the OE one. Try to get a better one if you can.

 

So I went through all the spark plugs today and inspected their wires & ignition coils. Didn't see any obvious issues.










I followed the factory service manual for Ignition and used a multimeter set on Ohms.

Measured the wires for resistance and they're all within spec.

High Tension Cord Resistance
Factory values: max 25 kOhm
My measurements:

Cylinders 1-4: 7.21 kOhm

Cylinders 3-6: 9.24 kOhm

Cylinders 5-2: 8.25 kOhm

Measured the ignition coils for primary resistance while cold (outside temp 70F).

Primary Coil Resistance
Factory values:
Cold 0.70-0.94 kOhm
Hot 0.85-1.10 kOhm

My measurements:

#2: 1.1 kOhm

#4: 1.1 kOhm

#6: 1.1 kOhm

Just as a troubleshooting step, I swapped Ignition Coil #2 and #4 with each other, as #2 is connected with Cylinder 5 which has been setting a misfiring code.

I noticed a wet spot under the Fuel Pulsation Damper on the Bank 1 Air Assist Hose connection. I ran the engine while keeping an eye on that connection but didn't see an active leak, so I sprayed it off with some cleaner and will monitor for the next few drives.









Found this video for replacing the damper and it looks very straight forward.



Not sure if this is the culprit or if I have a bad fuel injector. It looks the plastic cover on the damper can be removed for a closer look.
I'm gonna check the intake hoses for leaks and clean the MAF, IACV, and Throttle Body.
There is also a resistance check for injectors, that I might do if the issue is unresolved.

 

That damper is known to fail and leak as a result.

edit - 23207-20011 (replaces 23270-62010) is $80 for new OEM I see them used on Ebay for $25.

 

I'm thinking this would make sense why my Fuel Trim goes really high on Bank 1. The damper is on Bank 1, even though there is a crossover pipe to Bank 2.
Also it's closest to Cylinder 5, so maybe when it leaks that cylinder loses the most fuel pressure?
Maybe it's leaking intermittently and that's what's causing the rough idle, surging under heavy load, and maybe even the no-start when it was cold outside?