Rough Idle Sc300

[jbarhorst2]

Group,

a couple of days ago my '97 SC300 ran rough when I got back into the car after running an errand. The RPM was around 1200 or so and the rough idle lasted about 10 seconds. Then everything smoothed out and the idle dropped down to normal.

Here I am a few days later and I am still getting the problem on initial startup when the engine is warm. I have not noticed it the first start of the day. Sometimes it lasts longer than others.

I do smell raw fuel at the tailpipe when it is running like this.

I did a search, but did not find a situation that was exactly the same.

My MIL is not lighting up (it works, but no trouble codes).

Could a spark plug be going bad? I have not had one fail this way before, but there is always a first time.

Current plugs and wires are 55,000 miles old.

Thanks in advance for any ideas.

Tom

[jzz30]

if your getting in to the higher miles maybe a tuneup is needed. ignition components coil, wires, plug, cap, and rotor could be the culprit as you will not get a MIL in most cases just from some rough idle unless you get a misfire or knock or something of that matter.

[jbarhorst2]

Thanks for the reply.

Here's a little more info.

I am at nearly 214,000 miles.

The rotor, cap, plugs, wires, timing belt (and all associated stuff including water pump) were replaced about 59,000 miles ago.

This started just a few days ago (and rather suddenly I might add).

I am getting a nice plume of white "smoke" out of the tailpipes during this rough idling. Then the idle smoothes and about 30 seconds later (or less) the smoke clears. Sometimes the idle is rough for 5 seconds and sometimes it can be about 30 seconds.

The smoke, in my opinion, is not coolant. It does not have that sweet smell that I am used to. It also does not leave the greasy residue on your hands. I think it is raw fuel being vaporized and spit out the back. Is this possible/probable? What might be a likely cause for this? Could a fuel injector have gone bad to start causing this? Can it be leaking fuel into the cylinder after I turn the engine off?

I do not get the rough idle in the morning for the first start of the day.

Could something else be causing this condition?

I do get the trouble code 0401 periodically (EGR flow insufficient), but I have been getting that on and off for about 18 months. I have changed the EGR temp sensor and cleaned out the EGR valve with no results. The EGR valve is functioning.

I have not seen this before and am stumped. Thanks for any ideas.

Tom

[jzz30]

coil? if not might be injectors. but if it were injectors it would be constant.

[jbarhorst2]

If it is the coil could it be acting up only for a short time after I start the car?

I'm not real familiar with coils.

Thanks

Tom

[jzz30]

its possible... but i would try check the resistance first before jumping to conclusion. if possible borrow one from a friend if you know anyone with another 300

[jbarhorst2]

Uh oh.

My coolant reservoir looks lower tonight.

I'm going to mark it and check it every day.

The white cloud coming out of the tailpipe did not smell like normal "green" coolant.

Does Toyota coolant have a different smell when burned, or should it still smell "sweet"?

Interestingly enough I did not experience the rough idle today.

The saga continues...

[jbarhorst2]

Definitely burning coolant.

I had to add 1/2 gallon to get me back to my mark.

What is the most common failure that would cause this?

Is the head gasket the most likely cause?

Tom

[jzz30]

start checking your oil frequently! if it seems wierd like kinda watery then its probabaly head gasket. overheating will cause the gasket to go bad, but under normal use its unlikely unless you havent changed or added coolant since the car was new in wich case the head gasket may have erroded or coolant level got low and overheated a bit...

[jbarhorst2]

Well, it goes in the shop tomorrow morning.

I'm very curious.

I am a fanatic about fluid changes and it has never overheated to my knowledge.

I'll let you know what happens.

Thanks

Tom

[jbarhorst2]

It was the head gasket.

I also had 2 exhaust valves not seating, so I was losing compression on those cylinders.

I am having a valve job done and then they will put it all back together.

Tom

[UCF3]

Exhaust valves? Do you mean exhaust gasket?

[jbarhorst2]

No, actually the exhaust valves were not seating properly on the cylinder head. This allowed part of the charge to escape during the compression cycle before ignition in those cylinders.

That's apparently why I was smelling some raw fuel at the tailpipe.

They sent the head out to a machine shop and they reground all the valves and milled the mating surface.

It's being put back together now.

Tom

[WadeLovell]

No, actually the exhaust valves were not seating properly on the cylinder head. This allowed part of the charge to escape during the compression cycle before ignition in those cylinders.

That's apparently why I was smelling some raw fuel at the tailpipe.

They sent the head out to a machine shop and they reground all the valves and milled the mating surface.

It's being put back together now.

Tom

:cries:

I am having a similar problem on my 1993 SC300. I suspect the head gasket since mine overheated.

During the last 1,000 miles I have done the following maintenance on the Lexus SC300:

At about 146,500 we began experiencing an overheating problem. There were three incidents.

1. The first was the plastic top of the radiator cracked.

• Replaced the radiator with a new all metal radiator.

2. The second was the upper radiator hose burst.

• Replaced upper radiator hose and radiator cap.

3. The heater hose that connects at the back of the block burst.

• Replaced the lower radiator hose, thermostat, and heater hose.

There have not been any more overheating incidents.

After the third overheating related repair, the engine idled roughly when warm and threw EGR code #71.

• Replaced EGR vacuum lines.

• Cleaned and tested EGR valve. Seemed good but I replaced it anyway.

• Replaced the oxygen sensors.

• Replaced the coolant temperature sensor – the one the ECU uses.

Continued idling roughly and began throwing #25 Lean and #26 Rich error codes.

• Replaced distributor cap and rotor, spark plugs, and ignition wires.

• Ran a tank with injector cleaner.

• Added Slick 50 engine treatment for high mileage vehicles to crankcase.

Threw a #71 EGR code. The only remaining components there are the wiring and the EGR Gas Temperature Sensor. I accidentally disconnected the hose to the vacuum diaphram for the EGR when changing the PCV today. The #71 EGR code was a red herring (unless of course it reappears later).

What’s next?

• Run a compression test on all six cylinders. (140 to 160. I wish it were better.)

• May want to replace the fuel filter to rule it out. Do I have a fuel line pressure tester?

• Want to test the EGR Gas Temperature Sensor or replace it.

• Want to test the injectors and inspect the injector wiring.

Symptoms:

• Rough idle.

• Low power.

Suspect:

• Damage related to overheating once too often or for a little too long.

• Burned valve(s) from one of the overheating episodes.

• Bad head gasket from one of the overheating episodes (I have not noticed any white smoke or seen any loss of coolant.)

What did your head gasket and valve job cost?

Does anyone have any other ideas?

Thanks,

Wade

[jbarhorst2]

I have not gotten the final bill from the dealership yet because it is still in the shop.

Of course, I like putting the 2000 miles on their loaner for the past 2 weeks.

I think it will be in the neighborhood of $3000.

Odd that you have not noticed any coolant loss.

Have you checked your oil for coolant contamination?

Open your oil fill cap and see if there is a white sludge substance on the underside of the cap.

If there is, then you have coolant in your oil.

The dealership and I inspected my engine pretty closely while it was apart.

My cylinder walls still have the marks from the original honing process. They are in good shape. Compression is also good.

It really made me a believer out of the oil I use.

I only use Mobil 1 synthetic.

214,000 miles and no apparent engine wear.

I'll let you know the final bill once I get it.

Tom

[WadeLovell]

I'll let you know the final bill once I get it.

Tom

Thanks, Tom, I am a Mobil 1 synthetic man myself. There is not any evidence of a white film under the oil fill cap. As I mentioned, I recently added Slick 50's high mileage formulation to the crankcase. As soon as I have 500 miles on that I will replace the oil and send a sample to Blackstone Labs for evaluation.

Wade

[jbarhorst2]

Well, I got the call today.

My bill will be about $3,600.

That includes the tow bill ($220), the cylinder head rework at the machine shop, a new timing belt and tensioner, and some minor other small parts while it was apart.

My dealership warrantys everything for a year (unlimited mileage), so I don't feel too bad.

My next car is going to be an LS and to get what I want I will be paying about $700 per month, so as long as my car runs for 5 months, I am ahead of the curve. ha ha

Tom

[WadeLovell]

Well, I got the call today.

My bill will be about $3,600.

My next car is going to be an LS and to get what I want I will be paying about $700 per month, so as long as my car runs for 5 months, I am ahead of the curve. ha ha

Tom

OUCH! I got VERY Lucky. I finally pulled the throttle body to change out the #3 and #4 plugs and wires. Both cylinders had great compression. I thought one of them was certainly going to have low compression. When I put it all back together with new Bosch wires and platinum plugs it ran like it was NEW! It did finally throw a #71 EGR code after two hours on the freeway. Then the check engine light went dark again shortly thereafter. I will check the wiring one more time on the EGR temp sensor while my new sensor is in transit. If I don't cure the problem before the new sensor arrives, I will be forced to add it to the list of recently replaced parts. Still, the overall damage including the new timing belt (professionally installed) was just this side of $1,000. Now, if I can just get to 215,000 like you have without blowing the head gasket.

Wade

[jbarhorst2]

After my repair, my check engine light has not come on.

I was getting the light frequently for the EGR valve.

Since the head was sent out for repair all the gunk was cleaned out of it too.

I assume either that or my leaking exhaust valves were throwing the code for the EGR valve low flow.

Tom