Well the cat is no longer a possible suspect. It has been hallowed out. Today, the car acted up with its stuttering hard under anythign less than full throttle while it was still cold, and a ecu reset didn't help.

Could this still be the fuel pump ECU if it happens when the car is cold?

 

Well it did it today while it was cold. Now after resetting the ECU it still is running like total **** unless I go WOT, and holds a choppy idle around 200 rpm. Lots of unburnt fuel coming out of the exhaust.

Now i unplugged the MAF while it was idleing and it didnt change anything. Unplugging the TPS caused the car to jump back up to around 800rpm and idle much more smoothly.

I thought unplugging the MAF would cause the car to die? Am I wrong in thinking this??

 

yeah, normally unplugging the maf does it.... get a good one and test it out

 

If you get this unburnt fuel, either you are running too rich or not getting the proper amount of air to fuel mixture. When you unplugged tps, everything went smooth. So the car is probably not getting the right amount of air/fuel mixture. This says that it is probably sensor related. Try adjusting the tps using these methods:

https://www.clublexus.com/forums/sho...d.php?t=303991

https://www.clublexus.com/forums/sho...d.php?t=317900

 

This is your first clue.

Which is clue #2 that points to clue #1. It's the MAF. It is not your fuel pump ECU because that only controls slowing down the fuel coming forward, you have TOO MUCH fuel coming forward which means hardwiring the fuel pump to run wide open is only going to make the problem WORSE. What you have is a lack of management which should be restriction of the fuel, which is controlled at the MAF. The fuel ECU is only there to conserve gas. Even the people who have hard wired their ECU open to run the pump at full pressure are still able to control the fuel at the front because the MAF is controlling it.

I have a question for you. Since the time you purchased the car, did you ever unplug the battery or have any work done that unplugged the battery BEFORE the problems were obvious? If the answer is yes, it is your maf.

If the answer is no, it may have been done prior to you buying it and you not know.

The MAF "home" settings (as I like to call them) are a base reading of settings the computer stores and expects to see so it doesn't refer to them it only monitors the small changes overall. Think of it as a "cache" of computer memory, because that is what it is. When you disconnect the battery you reset the computer and it causes the computer to start from scratch on the readings rather than refer to the cache.

I have seen HUNDREDS of people who had bad mafs and did not know it until they unplugged the battery. Once you reset the computer, it becomes painfully obvious the MAF is not doing what it should. Most people that do this are complaining of poor operation and are trying to fix something on the car, not knowing the poor operation is because of the failing MAF.

Unplugging the TPS tells the MAF the TPS is actually idling higher than it truly is so the RPM comes up (removing the TPS makes the computer go to a preset voltage signal to replace the missing TPS. This can be verified by the average user with no issues unplugging the TPS and the RPM will skyrocket). It all goes back to the MAF. It is very unlikely the TPS because if unplugging it causes a change then it IS WORKING, unlike the MAF.

All components work together, each one causes a change in the system. Every one you unplug should do something to change the situation. When you get to one that doesn't change anything, that's your bad component. People use this method to check ignition coils. Such as when you pull a plug wire and the engine will drop RPM or miss. When you get to the wire that doesn't change anything when you pull it, there is the dead coil or fouled plug. This is because you remove a component that helps make the system run. You pulled the MAF and it didn't change anything..... aside of the other obvious points made earlier that point to the maf, the diagnosis is replace the MAF.

 

Thanks alot O.L.T. Your post definately confirmed my suspicions. I'll be getting a MAF asap. Thanks also for such a well thought out and executed post, that's a rarity anymore!

I'll report back....thanks for all the suggestions!

 

I decided to pull the codes on it and it gave me a Code 24. I reset the ecu and tried to start the car and now it just turns over and won't fire up...still showing a Code 24.

This code is for IAT I believe, Is there any relation to the MAF here?

 

Yup code 24 is the Intake Air Tempereature sensor circuit which is built into the air flow meter.

 

Hm that's weird, the manual says its an AFM for a 93 sc300. He has a 92 sc300 so I didn't think there was a difference. Well in this case you can blame the Lexus shop manual.

 

Well I'm about to burn the car. Got my MAF in the mail today and installed it. SAME THING. TURNS OVER BUT WON'T START! Won't start with the maf unplugged or plugged. Check engine light does not go off when you leave key in accessory, and the code is still a Code 24!

I'm trying to let the ECU sit and clear itself for an hour, but I don't think that will help! Please help, Riding my bike in this freezing weather is not cool!

 

to reset an ecu fully you have to let it sit for an hour usually with the battery unplugged.

 

I HAVE THE SAME ISSUE!!!

it happend when i put my Air intake on....

It studders so f***ng bad its like some one is hitting the brakes and gas over and over again... I pulled my mass air flow senser off and now it runs perfectly fine... BUT i get like 5 miles to the gallon lol if anyone else knows this problem PLEASE help me

Website to purchase a new one?

 

Did anyone ever figure anything out here.
2muchpsi, was it your maf in the end or do you still have the same problem?

 

Sounds like he needed to put a fuel pressure tester in line after the pump, and see what the fuel pressure was. Then maybe a spark plug tester to see if the spark from the coil is breaking up. Check all the grounds, Check for loose or broken wiring and connections at the TPS, IAC, MAF and so forth. Its nice to have someone that is very knowledgeable to suggest what it MIGHT be. Not diagnose the problem without touching the car. I hope everything worked out and he was able to fix it.

 

UPDATE:
THe car's symptoms got worse and worse till one day I limped it home and it woudln't start again. I found the valve covers were leaking so I replaced those gaskets, plugs, wires, distributor cap and rotor with all oem. The car starts up now, but runs like total crap.

I replaced the maf with another also, same exact symptoms. I tested both MAF's with the multimeter and both are within spec. Unpluggling maf while the car is chugging along at idle does nothing. Pulling the TPS raises the idle and the car stops misfiring. Still running rich (unburnt fuel in exhaust).

I went to pull codes today and now when i jump the TE1 and E1 pins I get a constant fast flashing CEL, that doesnt seem to go away with resetting the ecu. Because the car is OBD1, most shops in my area don't want to do diagnosis on it.

HELP!

Now i have a few more questions. What is up with the flashing check engine light. It keeps on flashing even when i start the car if i have the jumper wire in.