Yotarip

Well, I think my "no power/ limp mode" problem is solved with the advice of some of you guys here.

SYMPTOM as they escalated.
1) Faint stumble during acceleration that gradually gets worse.
2) Sudden drop in idle speed ( around 300-400rpm).
3) No power over 2000 rpm.
4) Somtimes the car will barely move forward when in "D". Must start off in first gear and manually shift.
5) Strong exhaust smell while running.
6) CEL is on but will not give a code.
7) the problem showed up and lasted for 3 days, cleared up on it's own , then returned several days later.
8) Finally the car failed to start at all.

I had changed the wires and plug prior to the problem BUT I did not change the cap and rotor. I finally changed the rotor/cap and the problem disappeared. The old rotor was extremely pitted and covered in black carbon. Some guys here suggested the cap/rotor and I shrugged them off. Well, it fixed my problem.

Thanks Guys

nthach

Try jumpering TE1 and E1 to pull codes. Sounds like you've got an issue with the MAF or TPS.

LiCelsior

iTrader: (32)

ignition coils could also be it. www.lexls.com is your friend.

MEANDAFAKA

so the problem was fixed after you changed out the cap and rotor?????

Yotarip

NO!!! 2 days ago the problem reappeared. It's strange because it ran great immediately after I changed the cap and rotor. On top of that, the idle speed jumped up to 1200 rpm.
Yesterday I downloaded the repair manual linked on LEXLS.com. I removed the idle air control motor ( the valve was in the OPEN position when I removed it) and checked the for movement of the valve as the ignition switch was turned on. It didn't move. I then checked for the resistance across the iac motor. I got a constant 45 ohms. The repair manual states anything over 30 ohms means the motor is bad. I also ran 12 volts directly thru the IAC as the repair manual said to check for movement but shuddered as if the motor was locked up.

BTW, IAC costs $650+. I dont mind paying it but I want to be damned sure that this is the problem. Tomorrow I will pull the ECU and check for signs of leaking capacitors on the circuit boards. There is a company that will repair the computers for $100.

I checked the resistance across both ignition coils and they are fine. I have a brand new tps from toyota and it didn't help. My maf is fine because I installed my maf on my buddies 92 ls400 and his ran fine.

LiCelsior

iTrader: (32)

try www.car-parts.com for local junkyards..see if anyone has a IAC. or u can pm ALIGA since he parts out SC400s so u can get a IAC from one of his junker cars.

Yotarip

LiCelsior, I appreciate your help. I tried something today.

UPDATE;
Today I went a a junkyard in northern VA that usually has 3-5 1uzfe powered lexus's at a tiime. I pulled the IAC from a 91 and a 95 LS400.

NOTE: The 90-92 IAC valves are serviceable, meaning they can be taken apart, inspected and cleaned. I measured the resitance across the IAC @ 23 ohms.

The 93+ IAC valve are NOT SERVICEABLE. I measured the resistance to be 45 ohms just like my 93 IAC.

I bought both the 91 and 95 IAC because they were from wrecked cars so I assume they may have been running fine before they found themselves at the JY. They cost me $6 each.

I connected 12volts direclty to each IAC an neither moved. I tore down the 91 IAC and found it was full of carbon. I cleaned it up with throttle body cleaner and made sure the bearing and screwdrive moved freely. I put it back together and ran 12 volts through it and it MOVED!! I installed the 91 iac on my 93 ls400 and found out that the metal nipple for the intake hose on the 91 IAC is SMALLER than the 93 IAC. I had to use a screw type hose clamp to cinch the large hose onto the small nipple.

I started the car, it immediatley stalled and the CEL was on. Several tries later the car would barely idle and the CEL would flash erraticly. The light would flash for a second and the motor would almost die, then the light would go out and it would idle up fine for a second, then the CEL would flash and so on.

Finally after many more starts and rests in between, the motor ran fine and the CEL stayed off. I will keep my fingers crossed and thrash the car around tomorrow to see if the problem emerges again.

06taco3UZ

I'm almost certain your Engine ECU is on it's way out. The dead giveaway (excuse the pun!) is that it won't flash error codes when Tc is grounded. Assuming that the ECU has power, ground and the Tc wire is good a properly functioning ECU will ALWAYS flash codes. If it doesn't then the ECU is faulty, end of story. The other symptoms of a dead ECU (corresponding to your list above):

1) See #3 and #5 below.
2) IAC motor random jumps or stuck in last commanded position.
3) Fixed ignition timing with no spark advance.
4) Transmission solenoids disabled, transmission reverts to hardware limp mode with current gear selected by lever position (D=4th, 2=3rd, L=2nd) no automatic shifts, no lockup.
5) fixed injector pulsewidth based only on rpm which is VERY rich.
6) microprocessor is dead so it is unable to enter diagnosis mode
7) as the hardware fails problems may be intermittent, worsen based on ambient temp and get worse over time until total failure.
8) hard starting due to rich mixture (flooding) and closed IAC

FYI, inside most OEM engine ECUs there are actually two separate systems that can control the engine: the primary system that is microprocessor-based (the "computer" part) and a "backup system" that is basically "hardwired" and takes over in the even the microprocessor stops running. Generally the "hardwired" functions ignore ALL sensor inputs (temp, airflow, etc) and command fixed fuel/spark, no idle control, no trans control, MIL on. This is different from what happens when a sensor fails and the computer ignores or substitutes it's value. Both are forms of "limp home" functions, one hardwired and the other implemented in computer software.

06taco3UZ

The reason the MIL light flashes erratically and the engine stops running properly at the same time is that "hardware" limp-mode I mention. The moment the microprocessor stops ("freezes") the hardware limp takes over and the 1st thing it does is turn the MIL on. If at any time the microprocessor restarts itself it will automatically take over and the MIL will go back off. What's happening is the microprocessor is repeatedly freezing and restarting itself, causing the erratic MIL flashes. The probable culprit is bad power supply caps resulting in noise and power instability within the ECU, very similar to what happens to the instrument clusters.

Yotarip

Thanks 06taco3uz.

That's exactly what I have been thinking the entire time. If the gauge cluster will work intermitently, the same can happen with the ecu. I hoped to find a 93-94 ecu in the junkyard to send out for repair so I wouldn't have to park my car. No luck with that because every LS in the J/Y has been raped of it's ECU. I decided to try the early model IAC as a final effort before I send the ECU out for diagnosis and repair. So far (36 hours later) the car is still running fine with the early IAC.

Yotarip

UPDATE!!,

The problem is BACK! CEL is on with high idle and no power. Today I am going to remove the ECU and overnite FEDEX it to http://www.foreignecurepair.com/rnrlexustoyota.htm for repair.

I'll keep you guys posted.......

RAINBOW

Yotarip, sorry to hear yours is kinda-not-fixed. I cleaned my MAF and installed a new airfilter (really dirty) last week and it started, smoothed out and has been running great. Drove it all day Sun. and no problems. Got in this morning to go out of town and it went about 2 blocks and "The EXACT SAME DAMN THING" drove back home and sat in the driveway for a couple minutes running. Idles good, good clean exhaust note from both pipes, romped on the gas 5 or 6 times and it sounded great with a clean exhaust. Turned it off to go get my piece of jump wire to check codes, and now it won't start at all, and my CEL would not light up even after several tries. Anyway it's dead and I'm going to let it sit...................I'll drive the Miata, it always starts and runs. Goodluck "Rainbow" A.K.A. J@#Junk

Yotarip

Well Rainbow, this problem may be solved.

Yesterday, I overnited my ecu to the repair company linked above. A technician called me this afternoon and informed me that there were a few leaking capacitors on the board. The fluid leaked onto other circuits causing more problems. I braced myself for the total cost of repair and it was still $250. He said he will have it fixed in a couple of hours. Cool, I also paid an extra $30 to have the ecu shipped to me overnite.

I'll keep you guys posted.

Yotarip

OK,

I received my repaired ecu yesterday and installed it today. They attached a seal on the ecu that if removed, voids the warranty.




She runs great. Even the very, very, slight stumble it always had during acceleration from a stop is gone. So far so good..

Once again, thanks to 06taco3uz. Your explanation of the problem really helped.

RAINBOW

I hope that this is the end of the story. You ought to write a BOOK. Maybe it would pay for some of the parts you've installed recently ! I came home today from a trip (in my rent-a-car) put the key in mine, turned it on CHECK ENGINE LIGHT WAS BACK. Started right up, ran for 30 secs. CEL came back on and it died. Sound familiar ??????????