DRFT86

Now first let me just say that I have done some research on this for the past two days and tried different things but have come up empty. So I am resulting to this post, hope someone can spreak some knowledge.


I am having a random issue with my 92 lexus sc300. I drove it daily and had no problems with the car. I didnt drive the car for two days and go back to drive it and it runs like complete ***. Barely idles and barely runs. I know that is is running lean b/c I pulled a plug out and it is white. Also the Check engine light came on, read the codes and I pulled 24 and 31 which are air intake temp and mass air flow meter.

I went to my job(performance shop) and got a new maf for it and installed it and nothing changed. The IAT went off for a while and eventually came back on. With the car running if you unplug the connector on the maf it doesnt change anything. I am kinda stumped on what this is. I have heard something about the fuel pump ecu going on and cancelling it out.

With the things I have listed is that around the ball park of the fuel pump ecu going bad?

DRFT86

16 views and no idea?

No idea

soarer13oy

iTrader: (13)

try the 12v fuel mod see if its the ecu is bad

DRFT86

Did that and still nothing. Still throws a iat code. Im going to switch out the ecu and see if that works I guess.

WadeLovell

iTrader: (5)

When you say it is, to paraphrase, "barely idling" do you mean it has a hunting idle (say 1100 rpm then dropping to 700 or 800 then stumbling and almost or actually dying, then revving back up)?

WadeLovell

iTrader: (5)

When you say it "barely runs" do you mean it has limited power? Shakes? Stumbles? Cuts out completely at 3100 rpm?

WadeLovell

iTrader: (5)

I have had a series of problems and been through a lot of parts. My expectation is the IAT is related to a bad sensor. They tend to degrade over time, the connectors fail and the insulation degrades. The last one I took off separated into two parts while I was trying to loosen the harness connector.

WadeLovell

iTrader: (5)

The new MAF would have been first on my list if I weren't paying retail. However, I think it is a red herring.

You are not getting enough fuel for the amount of air. You are running a naturally aspirated car so there is only so much extra air the system can add under any condition. The fact that disconnecting the MAF (going into limp home mode) does not affect it, suggests to me you should be checking the fuel pressure at the rail at idle and, if you have the capability to test it, under running conditions. You have already done the mod so the Fuel ECU is out of the picture.

MooJohn

Don't shotgun the repair. The ECU is telling you something is wrong with the IAT input. If it isn't the MAF, and we know it isn't since you tried a new one, something is wrong with the ECU.

Pull it and behold your leaky capacitors.

Reesetrict

iTrader: (1)

Worth a shot. You have to look REAL mufuggin close sometimes. When my ECU fried I looked at every little solder on both boards. About to give up almost at the end of the 2nd I noticed a slight discoloration on the foot of a cap. Voila. I tried to replace it but I solder like a kid with palsy. I didnt realize at the time that my across the street neighbor is an electrical engineer that was working for NASA(now works at toshiba). He has a bad *** setup in his garage. He could have hooked me up with the skill of a brain surgeon.

HOWEVER, when my ECU crapped out (ran like hammered *****, it ticked, and went into limp mode only allowing like 2500 rpms) it wouldnt throw code. CEL was lit, but no code.

IAT sensor mb? Its gotta be one of the two.

2jznosht

Ecu, pump Ecu, or the fuel pump

DRFT86

i replaced the ecu with a known good one and it still throws the iat/maf code. So in total I have tried a different maf, ecu, and fuel pump ecu.

The symtoms are:
When I first start it, it starts fine and idles fine. Then after 30 seconds it bogs down and has a very bad idle, engine shakes. When revved it sputters bad like in stages. That is why I thought it would be the maf but with the maf plugged or unplugged it runs the same. it will rev up as high as i want but has no smoothness to it. Also it is running lean, not rich. Which I thought usually on obd1 cars if a maf is bad it would run rich. What is the sensor to the left of the tps closest to the throttle body(looking from the front)?

Ive been told that its a possible o2 sensor as well but its not throwing that code.

This is very annoying, and for it to happen all of a sudden is very strange to me.

MooJohn

Since you've tried so many parts, the only thing in common with every combination is the wiring harness. You've got to have a wire or plug issue somewhere. It's the only part that hasn't been ruled out.

I have to assume the sensor you're asking about is the traction control. I have a 400, and I don't happen to have TC, but Toyota has used the same form of TC for quite a while on all their cars.

619Rider

A while back I had an issue on my sc300... and it will run fine for alil while and then it will die.. and wont start for several minutes.... and run like crap.... so i did the 12V mod and it worked flawlessly.. it ran for 4 months before my engine bearings took a lil dump on me.....

DRFT86

I guess I will take a video of the symptoms and point out the sensor that Im talking about. Man, I can usually get this stuff knocked out pretty quick but this one is a little weird for my taste.