gtsfire

iTrader: (4)

Good evening everyone. A friend of mine has a 92 SC300 5-speed that currently has 66k miles on it. It has recently begun to have some idling issues. Sometimes when you let off the pedal it'll just die and then sometimes it will run like new.
Back story here: A few months ago upon start up he noticed it would shoot a puff of blue smoke and smell very rich but would then be ok. He took it into his independent Lexus mechanic and they did a complete tune up, plugs, wires, cap and rotor. Not long after that is when the idling problems started. It is not throwing any codes and the CEL is not on. He did admit to using low quality fuel so I suggested that the IACV may be the culprit and and that he should start using a Top Tier fuel and throw a can of Seafoam in the tank. He did have the IACV replaced and it worked fine for a few days and now it has resumed dying when you let off the pedal. It also has started to run rough when you floor it but says it smooths out when you back off the pedal. When I looked at it all the vacuum lines appeared to be in good order. I've been searching but cannot find a thread with similar issues. He is not on the forum so I told him I'd ask about it. Any help/advice would be greatly appreciated.

KahnBB6

iTrader: (5)

gtsfire, has your friend ever had the car's ECU sent in for capacitor repair? That is one thing I would suggest he rule out even with a 66k mile car since it is 1992 vintage. We recommend Tanin Auto Electronix for this service. And since he has a 5-speed model and the ECU is a bit more difficult to replace in an emergency I would highly recommend insuring the package both ways for at least $200 with a NON-overnight shipper (Fedex is best... just DO NOT use their "Overnight" service) and require Adult Signature Upon Delivery. He should do this for both sending and the return shipment (Tanin can arrange those shipping options for the return if you ask them to).

That is one of the more common quirks of these cars that should be ruled out as they have aged so much. It's due to a certain choice of capacitor Toyota used in many of their engine computers from the late 80's until early 2000's.

Having replaced the IACV is good (was this with another used one that was cleaned up or a new OEM? Or an aftermarket IACV?)

The standard tuneup is good.

I'd recommend only using premium gas but there has been a recent discussion thread on that topic very recently which is worth reading.

How recently were the O2 sensors replaced?

Is the blue smoke on startup a consistent thing? Is this noticeable after the car is warmed up or when at wide open throttle under load?

gtsfire

iTrader: (4)

He said the IACV is new Toyota part. Doesn't matter if engine is hot or cold. The O2 sensors have not been replaced. Since replacing IACV it intermittently runs very rough at WOT but smooths out when he lets off the pedal. Still dies at stop lights and such if he lets off the gas. I know the ECU has not been touched.

Coleroad

+1 on the ecu repair. Especially when it has been in the hot Texas climate. Even if it hadn't been in the hot climate. Like was said very common problem with this car. Another thing and not saying it is, but just for reference don't rule out new parts. Sometimes new parts do get shipped that are defective. I would send in that ecu

eknine9

iTrader: (8)

I recently had a very similar problem with my 92 5speed as well.

Have him start with the ECU, the capacitors had an incorrect salt used within them so they slowly corrode their casing over time. Tanin does a very good job and I used them for my ECU, however even though my ECU had a leak replacing it did not fix the problem for me. My problem was caused by a faulty coolant temp sensor.

I unfortunately replaced a myriad number of other things chasing this down. However it's very important to do the ECU now anyways, if that doesn't work have him try the coolant temp sensor. When it goes bad the car no longer knows how warm the engine is, and it determines how much fuel to put in the engine based on the engine temp.

This is the thread, I'm a bit embarassed by it to be honest. I consider myself a car guy, yet I spent over a year replacing parts, and having the same problem pop up again and again and again on me.

https://www.clublexus.com/forums/per...d-igniter.html

Mine would do the same thing where anytime you let off the pedal once the car was warm it would die if it was acting up. Other times I would go out for an hour long drive and it wouldn't give a problem. There was smoke at startup and a rich fuel smell from the exhaust. It wouldn't idle properly. Sometimes when it died it would not start backup because too much fuel had been dumped into the cylinders, at which point i had to remove the throttle body and spark plugs to clear the cylinders before it would start again.

Start with the ECU. If the problem persists, then move on to the engine coolant temp sensor.

Here's a thread with the coolant temp sensor location, it's much easier to reach if you remove the power steering pump.
https://www.clublexus.com/forums/per...999-sc300.html

Here's another thread
https://www.clublexus.com/forums/per...-i6-sc300.html

Make sure not to lose the gasket when you do this, it's necessary to use the old gasket on the new one, or to buy a new gasket for the new one to prevent leaks.

KahnBB6

iTrader: (5)

^^ eknine9, I went through a similar months-long confusing repair process recently myself so don't feel embarrassed. If we haven't gone through these issues before ourselves we're going to just start with the most likely culprits first and more on down the line until the engine issue is finally resolved.

I completely blanked on the ECU coolant temperature sensor. Yes, OP, I'd recommend this as well if ECU repair does not resolve the issue. The OEM Toyota sensor and a new Toyota gasket is what I recommend. It's a cheap metal gasket to replace so there is no reason not to do it at the same time. Have another gallon or two of extra coolant handy if you choose to replace it without draining the engine coolant first (and put a big catch pan under the engine before you to this).

The second thread link above explains how to do it yourself and has the part numbers for both the sensor and gasket as well as the torque setting required for that sensor. Also note that there are TWO coolant temperature sensors on the 2JZ-GE engine: one is for the analog temperature gauge in the instrument cluster and the other (the one we are talking about and the one that helps govern startup idle and full temperature idle) is for the ECU to know the engine temperature.

This one, as eknine9 posted:

https://www.clublexus.com/forums/per...-i6-sc300.html

Focus on getting your ECU serviced first however. That should be #1 and something to have done anyway for the long term health of the car.

Mephobia

I had that problem 2 years ago, I replaced the ECU with a used one and all was well. until last weekend the second ecu went bad. Now I have the fuel smell and smoke back. I intended to send both of the bad ecu's to tanin tomorrow so I called them and explained the situation, they said they can't fix it and gave me the option of buying a refurbished one for 300 plus shipping. I'm thinking about trying Aaron at drift motion.

TaninAuto

1999 ECU's are completely different from 1992-1996. We also are not repairing ECU's that we cannot plug into our test vehicles to ensure they start and run.

gtsfire

iTrader: (4)

His is a 92 factory five speed. I'll tell him about your website and have him contact y'all.

Mephobia

I'm thinking there must have been some miscommunication the ECU's I'm speaking of are both from a 92 five speed 300's

RXRodger

iTrader: (2)

Didnt you say the car ran fine until the tune up? When you replace plugs in these cars you have to remove the Y pipe of the intake manifold. I would start there. Depending on how the mechanic removed and replaced this intake manifold there is the possibility he messed up a gasket and the car is leaking air there. Just a thought.

TaninAuto

In that case send them in and we will see what can be done

gtsfire

iTrader: (4)

He got the ECU back and installed it yesterday and he has said that so far the car is now running great!