I have a 1993 SC300 Auto. It has two issues and I am hoping they are related.

Issue 1. Cold start. When you start it cold, it fires right up but then idles awful, it revs up and down between about 1200 and 500RPM, it will normally die but if I rev it to about 1500RPM for about 2 to 3 minutes then it will idle fine under 1000RPM. It is only like this for the first few minutes.
Issue 2. Hesitates. This is driving me bonkers. When driving and let off the gas and then give it a little gas it will hesitate for a second and then go fine. Same as when at a stop light, a little gas and it hesitates and almost dies and then goes fine. If I give it half gas or floor it and it is fine.

Steps done, previous over has replaced said he replaced the distributor but I am thinking he meant the cap, but the wires are new and so are the plugs. I have checked the air cleaner and cleaned the MAF (thing in the air intake) but still have the same issue.

I have run fuel injector cleaner through it and only run super unleaded.

Any ideas?

 

1) If you ran any kind of cleaning agent over the SENSOR part of your MAF unit (actually a Karman-Vortex sensor in 1992-1995 SC300's) then you have probably damaged it. This happens a lot because not everyone knows you absolutely *cannot* clean that sensor. Ever. At all. Never. I am sorry to inform you that it is possible that you may need to get a replacement off RockAuto or ebay now for a good tested working used example. You will only need the sensor itself, not the entire aluminum housing. Very easy to replace.


2) Your symptoms before cleaning the KV MAF sensor sound a bit like an Idle Air Control Valve that may be malfunctioning. Check into that after addressing #1 and #3.


3) Have you or had the previous owner ever sent your main ECU in for new OEM-brand and OEM-spec capacitor replacement service repair? If not that could potentially be part of or the root of the issue since all SC300's, SC400's and other 90's Lexus and Toyota models tend to have issues eventually with old capacitors failing or worse leaking electrolytic fluid.

We recommend Tanin Auto Electronix for ECU service and repair. This is now a special request through them via phone or email but they can still do it on a case by case basis even though they no longer advertise the service directly on their website.

It is a good long term maintenance rule of thumb these days to get SC ECU's serviced for this but especially so if there are running issues. Here's the main thread that explains this common issue in detail:
https://www.clublexus.com/forums/ls-...capacitor.html


3) A recent poster not only replaced the distributor cap and rotor (stick to OEM Toyota/Denso parts in this case-- they are just made FAR better than any aftermarket alternative) and ignition wires but also the distributor unit itself. Usually the shaft O-ring may need replacement after many years but if there is an internal leak or issue with the cam position sensor housed within the distributor unit then it would need replacing. If you don't have the latter two issues then you don't have a problem with the actual distributor unit.

The distributor cap, rotor, plug wires and spark plugs are due for replacement every 60k miles in the 92-97 SC300's.


4) These cars require premium fuel only (91 octane or higher) so your fuel choice is good. Injector cleaner may help if needed but a new OEM fuel filter to replace a REALLY old one is usually all the fuel system needs. The OEM fuel pressure regulator lasts a long time in these cars but eventually those can sometimes need a new OEM replacement as well.

If there are issues with clogged injectors it's better to remove them and send them off to Driftmotion (Montclair CA) for a sonic cleaning service or to Five-O Motorsports for the same fuel injector cleaning service or to exchange them for a fully cleaned and re-balanced OEM exchange set. When getting a new OEM set from them you'd need to reference the Denso/Toyota part number located ON your injectors rather than the Toyota part number you'd find in the official Toyota parts catalog.

I would not get into injector replacement or sonic cleaning right now. The main suspects are your potentially damaged KV MAF sensor, the ECU and possibly your Idle Air Control Valve but only after ruling out the first two.

 

check your plugs/valve cover gaskets- i had a light misfire due to some oil in the spark valley

 

Did you fix the problem? Check your Idle Control Valve
and only use genuine Lexus brand as the non-manufacturer brand also throw a rough idle.