lex1220

Okay so I have a 92 sc300 and I can not solve this problem for the life of me. The car will not start unless I give it gas. and continue to give it gas until it warms up enough that it holds idle on its own. I tried cleaning the IACV and did a few service manual tests on it to see if it works and it did. I checked my TPS, same thing. I noticed though that when the car is running if I unplugged the TPS or IACV nothing happened. It ran the same. This leads me to think my ECU has an issue.. a big one. Does anyone know of how I can find out if my ECU is going bad? or of a place besides lexus I can take it and have them find out? I mean the car runs and drives perfectly it seems once it warms up after a minute but i'd still like to figure this out. Any help would be great! thanks.

Ali SC3

iTrader: (10)

best bet is to check the ecu, remove it and open it up and check for any burnt areas or anything leaking (capacitors). there are companies that do ecu repair for you if you cannot tackle the above yourself, i think driftmotion does it. only other thing i can think of besides a bad iacv/tps/ecu is an intake leak.

lex1220

I doubt an intake leak would cause the computer not to respond to unplugged sensors. Would the computer throw a code for an unplugged TPS? I know it does for the ECT sensor. I know it is supposed to throw a code for bad TPS but what about unplugged? I would think so. I love this car but at the same time I hate it lol..

lex92sc300

iTrader: (3)

Does it throw any codes at alli know a o2 senor can cause what you describe reset computer remove battery cable and try and see if it does same and throws a code run it a while till computer reprograms self if it cant will fail to open loop and o2 could cause what you describe

lex1220

Ive done all that. I know if I unplug my ECT sensor it will throw a code but Im pretty sure it should still respond to an unplugged TPS. Ive been working on this for months. I can get my ecu rebuilt/reflashed for $250 but if its not that then id rather spend the money on the right component to fix the issue.

Ali SC3

iTrader: (10)

If you unplug the IACV, the plunger remains in the last position it was in, which means you would not notice any change in idle. If you unplug the tps while you are idling im not sure if you would notice much change or if it will throw a code, if its normal for it not to throw a code then its not that the computer isnt responding necessarily, it just knows how to idle still with a few failed sensors, maybe see if it revs the same with it plugged and unplugged. I would go unplug and let you know but I dont have a stock ecu anymore or a working cel so thats of no real help.

If you had an intake leak it would have the most affect on the engine when it is cold as thats when its pulling the least vac so there is a major difference between what the maf is reading and whats really entering the engine. when you crack the throttle blade you are increasing the volume of air entering the engine, which means the leak has less of an impact and goes unnoticed. when the engine warms up it can compensate for the unmetered air once it enters closed loop.

I was just trying to list out the possibilities its a really small chance its an air leak but it could be. In all honesty it sounds like your IACV is not working properly or the ecu is bad. it takes maybe an hour to pull the ecu and check, that should be your next stop if you have tested the IACV. good luck.

lex92sc300

iTrader: (3)

If tried all that above wouldbe my next step

lex1220

How do I tell if the ECU is bad? I mean yeah I can look for friend spots or bad capacitors but is there anymore things I should look for? I wouldn't put it past the IACV to be going bad or working sometimes, failing. This problem happened after I took the IACV off to clean it.

lex92sc300

iTrader: (3)

If you have some one close u can borrow there computer gor a test change it out see if any changes
..go get a iavc from algi on jere or junk yard put it on. Just got to start eliminating things in some cases.

spoolxexo

iTrader: (4)

If you open the case and smell burnt fish, then the board is fried pretty good.

Usually you can tell right away from the Acid damage caused by leaking capacitors.

I have to pedal my car a lil to start too, but then it runs like a champ. I live with it.

lex1220

Ill check it out. Yeah the problem doesnt bother me too much since the car drives like a dream after it warms up but id like to know what the issue is cause a bad computer doesnt mix well with boost and I want to boost it.

TechGreek

iTrader: (4)

Check your coolant temperature sensor. I'm willing to bet money on that being the issue, if you replace - use the OEM. Check the resistance and plug voltage with a volt meter don't just throw parts at the situation.

Idle Air Control Valve usually only adjusts if a major change happens (A/C engaged, cold start, etc).

TPS won't do anything but use a limp home model value when unplugged.

lex1220

I have a new ECT sensor. That was what was originally bad. Also I just noticed; When I turn my A/C on only SOMETIMES does the idle adjust itself, sometimes it stays low.

TechGreek

iTrader: (4)

Is it OEM?

Please check grounds on LIM by oil stick. The IAC operates off of these big time.

lex1220

No the ECT sensor is not OEM, it's from Advanced. Why? Is there a huge issue with ECT sensors for these cars not being OEM? I checked my grounds, I found one undone but it wasn't LIM ground. I fixed it and it didn't solve anything.