Armitage

Hi All,

I have a 1993 Toyota Crown with 1UZ engine and 12,000 miles (very low miles!) which is currently giving me some trouble. I have both TRAC off and TRAC on lights engaged on the dash as well as a warning telling me to check engine, therefore I've jumped the pins to diagnose the TRAC system and received these two error codes - 48 and 51

48 - Sub-throttle position sensor signal is 4.3V or higher, or sub-throttle position sensor signal is 0.2V or lower when idle switch is OFF
51 - Problem in engine control system

Current issues are:

Hunting idle on startup
High Idle
Engine bogs/hesitates when gas pedal is blipped, but gas pedal being steadily depressed is okay
Slow Acceleration, can't even go up car ramps unless I get a running start

Things I've done thus far:

Replace IACV
Replace O2 sensors
Replace fuel filter
Tested ignition coils (resistance tested fine per the manual)
Pulled the ECU and inspected for any leakage or swollen capacitors but none were found

I also bought a used TPS to replace the sub-TPS (TPS furthest away from intake manifold but this didn't seem to fix the issue. However, now that I think about it I may not have lined up the sensor correctly).
I plan on pulling the throttle body to give it a good cleaning.

I'm a bit stumped that I can't solve this problem. Does anyone know of anything else I can test or replace?

LeX2K

There is a sub TPS? I can't find it in any diagram got a part number?

Armitage

It's essentially a second TPS on the 1UZ engines with TRAC. For instance, the # on mine is 89452-50020. From what I can tell it's the same as a regular TPS but the plug is keyed slightly different so if you want to replace it with a regular TPS model you'll have to shave the plastic side off so it'll fit.

Yamae

He would be almost a God who can judge just seeing the capacitor. A skilled guy would judge it measuring the ESR or measuring the actual ripple voltage.
There were many Crowns sent to junkyards due to the QAS capacitors issue,I must add.

RA40

iTrader: (6)

Forgive me if I've missed it... What years were these QAS type capacitors were used?

Yamae

Toyota had been in use of QAS capacitors starting sometime in 1989 or 1990 and ending sometime in 2000 for bigger engine's ECUs. The very early 1UZ-FE engine's ECUs were equipped with capacitors manufactured by Marcon which did not contain QAS liquid but had some problems at colder places like Alaska, Canada, some states up in north and Hokkaido Japan caused by the increased ESR when cold. Then QAS capacitors manufactured by Nichicon were introduced and the results were very good but there started to have different problems after a decade+.

deanshark

Nice low mileage there.
I had the same symptoms with the same codes on my 93 LS400 after about a year of owning it and I went nuts trying to track down the problem. I also looked inside the ECU and saw nothing wrong.....but unknown to me at that time, there was the problem. I eventually switched the ECU and everything came back to normal.
My suggestion would be; seeing how you can't see the caps leaking yet, have your ECU rebuilt with the good caps. Catch it before they leak and ruin the board, like mine eventually did and couldn't be repaired.

Got any pics of the 93 Crown?

YODAONE

If not the ECU capacitors, then check MAF sensor

Armitage

Luckily I did order replacement capacitors so I will pull the ECU again and get those soldered in. After seeing so many of your helpful posts I was hoping you would reply, Yamae

I'll try and take some once I clean her, she's a bit dirty after sitting in the driveway for awhile!

Thanks! I do see some cracking in the rubber seal surrounding the top. I'll put some sealant on it just in case and see if that helps

Yamae

Good for you. It is a smart idea to replace those QAS capacitors before the leakage starts. They do fail as aged and the leaked liquid (very strong alkali) kills the board and parts around. A proverb say, "Strike while the iron is hot" and I say "Replace while not leaked yet". New capacitors will give you some better engine performance result. Many people feel and report so.

Armitage

Well just an update to the thread -

Replaced all the capacitors on the ECU. I'm not sure if I was blind when I initially looked at it but one was leaking quite bad and even caused corrosion on the board. Fortunately, I did what I could to clean much of the leakage up with isopropyl alcohol and replaced the capacitors. Car runs well now, just troubleshooting some unrelated minor miscellaneous things. Thank you everyone for your suggestions!

sdls

great job!

Yamae

Congratulations on your success. Incidentally, does your Crown Majesta have an EMV (Electo Multi Vision) monitor and working OK?

Armitage

Nope! I think it's capacitor problem as well. If I press power on I can see the screen light up for a tiny bit then slowly fade to black.

Yamae

It sounds like the back light is no longer working well. I don't know it's a capacitor issue or not. I imagine that the CCFL is about to die or the high voltage drive circuit is not functioning well enough. I'd simply use LEDs replacing the CCFL.