scblackout

iTrader: (2)

Backstory:
96 sc300 with 200k, was running amazing but did have check engine light on for 2 o2 sensors and lean in bank 1. The o2 sensors were replaced but code remained. So I sent in the ecu to tanin. After receiving the ecu back I instantly had a problem code 340 for the crankshaft sensor and the car would barely run. It sounds like it has a huge cam in it with a fair amt of shaking and there is virtually zero power when driving it.

After about a half dozen restarts the car decided to start up and run perfectly. The 340 code was gone and just the o2 sensors and lean code remained, so it was just like before.

Well on 5 different occasions now I have started the car and it either starts running bad from the very beginning or starts running bad later. For instance I was 100 miles into a highway road trip a few days ago when the car started running horribly again. It stayed that way all the way home (30mph in the freeway is no fun).

So an hour later I start the car to take it to the dealer for a code pull and it is perfect, zero codes, no driving issues.... NOTHING CHANGED to cause this.... So today, I get in and it starts horribly yet again.

Lexus can't even give me an estimate within a 3k range believe it or not, so I am not going that route.

I have been told that if the ecu is bad, it is bad and the car wouldn't have 'good days' running perfectly. The same goes for crankshaft sensor, maf, o2 sensors, plugs wires, etc....

I have changed every single rubber hose in the car to remove any possible air leaks. When I spray engine starter around all the hoses there is no longer any increase in rpm. Changed the pcv valve as well just in case.

I am assuming that it can't be anything internal to the engine as it would never have a 'good day' if something was broken inside. So guessing it is electronic/air related?

So I am totally out of ideas and hoping someone else has had this problem that can lend some advice.

thanks

Ali SC3

iTrader: (10)

sounds like the rotor in your distributor has finally given out, cause it will mess with the crank sensor in there when it decides to misbehave, eventually it may run like that all the time if that is the case.
what happens is the rotor spins around delivering spark to the points on the cap, over time it wears down, and then the spark doesn't get to the cap so it doesnt get to the plug (even worse this now rogue spark can interfere and eventually damage the crank and cam sensors in the distributor). when its starting to get bad it will randomly drop cylinders and sometimes not drop any, which sounds like what you are experiencing. it usually gets worse and leaves you not being able to drive it anymore (has happened to me). next time it happens try giving the distributor cap a love tap with soemthing plastic, don't hercules through it its just plastic. jumping spark is not the best thing to have which is why I always replace the cap and rotor on cars that have them right away. its one of those things that will happen someday if you ignore it and leaves you stranded... there goes that camping trip..

when was the last time you did the cap and rotor on the distributor? if you have no idea check those out now its like 3 philips screws to remove the cap and 2 more to remove the rotor.
you may find the cap screws strip easily and you can also use an 8mm socket on them.
Dont drive it around you can mess up the crank sensor in the distributor and then you will need a new distributor not just the cap and rotor.

scblackout

iTrader: (2)

I had the cap rotor wires and plugs changed on the car and since then I have not had the horrible crank shaft sensor problem but do still have the lean in bank 1 check engine light on. Pretty much the only thing left to consider changing is the injectors.

The shop can hear a very slight exhaust valve clatter, though very hard to hear and minor. A compression and leakdown test is being done today so that might provide a little more info. I've searched pretty hard but have not found a good thread on what acceptable cylinder pressure leakdown rates are so hoping someone here as good numbers to go from. As for the tuneup the closest I could find was to time the car at 10 degrees or slightly lower.

When we find the actual problem then I will post back the results to help others out with the same issue.

scblackout

iTrader: (2)

Almost a month later and the car was delivered back to me yesterday. The car ran great with no check engine light on for about 10-20 miles. Then the 'blub blub blub' sound came back while I was doing about 20mph. It is like there is 5% of the power available. Only this time the check engine light is NOT on. The bulb works when I turn the key, but when plugging a computer into the car, it shows zero problems. Makes no sense. Yet every time I start it now it runs horribly. Yet I know that tomorrow it might run right when I try it....

I have replaced the ---- cap, rotor, wires, plugs, every vacuum line -- no leaks confirmed. cleaned the maf, replaced the air filter, sent the ecu to tanin for a rebuild, triple checked the wiring harness wires that I can see, replaced the fuel filter and the fuel line to the tank as it was crimped..

Any ideas what else I should replace or another way to diagnose the problem?

If the regular obd2 reader says it is ok, is there anything that the actual Toyota computer will show that they don't? ... hate to spend dealership money on this if I don't have to.

scblackout

iTrader: (2)

I may have found the problem and hope that if it does solve the issue that this helps someone else in the future.

I had replaced every single vacuum line on the car and did the pcv valve with new grommet at the same time. Well I decided to pull the covers to check the plugs again and noticed that there was some type of fluid around cyl 5 and 6. So I took a vac and rag and cleaned it all up. Started the car and it ran great. This got me really digging around for what could cause the fluid and sure enough it was the pcv grommet. Upon close inspection it was obvious that it was produced wrong and one small side was totally flat so that it could not seat properly into the valve cover.

So I replaced the grommet and the car continues to run great. Hoping this lasts longer than a couple of days which has normally been the case.

*The annoying part is a $3 part that I had just purchased ended up costing me hrs in the shop. The grommet was close enough that it was not apparent there was a leak until the engine heated up and the pressure would slowly unseat the grommet thus leaking oil into my plug channel. So next time you replace the pcv grommet, make sure to check that it was manufactured correctly as it will save a ton of headaches and expenses.

scblackout

iTrader: (2)

Two weeks later and zero issues. It was the stupid pcv grommet. So for anyone else getting codes all over the place where the car will run perfectly and then all of the sudden drop a cylinder and then repeat, check your grommet. In my case just enough oil would splash out of the grommet and would end up fouling out the plug wires.

eknine9

iTrader: (8)

Wow thats one of the worst experiences I've heard dealing with these cars. Glad you fixed it, and hopefully no one else has to go through this nonsense.

yauny

Mine runs like that but I never have good days. Won't go over 2500 rpms and isles like crap and wants to shut off says bank 1 cam sensor. Replaced both cam sensors spark plugs and wires and new ecu still throwing that damn code driving me insane trying to find a fix but I dont think mines gonna b a grommet

Ali SC3

iTrader: (10)

yauny start another thread with all your info and members may be able to help you out.
if yours is a sc400 the cam wire can get chewed up by the accessory belt give it a look.
sc300 then all the cam and crank sensors are in the distributor.

scblackout

iTrader: (2)

Unfortunately this did not solve the problem. After a week of the car driving perfectly I was pulling onto my road and I noticed my fan started blowing high-low-high-low and within seconds the engine started sputtering a little. It became progressively worse as I drove the 2 blocks home to where when I arrived it was as bad as before.

The next morning started just fine and within a few blocks the same problem.

I checked the voltage and I have 12.4 off and 13.6 idle so that is ok.

As the car started acting up when at temp I thought just maybe it had something to do with the cooling. After getting the car to temp (1/2 on gauge normal position) I noticed that the top radiator hose was quite hot and the lower one was completely cool to where I could hold it indefinitely without fear of burns.

The radiator was full and the fluid looks perfect, no oil sludge etc, actually was surprisingly reddish clean color. When I press on either hose the other would expand a bit so the radiator is not blocked. (car has never overheated on me).

So I am changing out the thermostat and hoses (once I find the best ones to purchase).

I can't imagine that this could be the cause of the rough running at times but it is one of the last areas I can think to try as 90% of the time where the car begins to idle and run horribly is when it is at temp, though not always.

Part that is hard to understand is no cell light when the car is running rough. It is so bad you can barely make it a block but the computer says no issues.. confusing.