Ken2012

Hi everybody, I just joined Club Lexus to find out more about my 1994 Lexus SC400 and a recent problem. I've been restoring the car for the last year. Since the tune up last month, NGK Laser Platinum spark plugs and NGK ignition wire set, the left muffler (area) "pops" every 8-12 seconds at idle and the car shakes at 40-50 mph, not during acceleration though. The shop had ordered air flow sensor O-rings from Lexus which weren't available; you have to buy an entire $800 unit to get the new O-rings. So the shop modified the O-ring mounting to increase contact with the air flow box. This really had little effect. At first, the thought was bad gas or the car had set idle for a long time; filling up with 87 octane was another possiblity since my other cars take 87; not likely I did. I fill up with 93. The car has improved some; however, not as much as before all these improvements. I may need to take to Lexus to check the codes; the special Lexus connector isn't available at the auto parts stores; any ideas or experiences with this problem would be appreciated. Thanks, Ken

1JZPWRD

iTrader: (59)

how long does this symptom actually last when it does happen? Have you checked the timing just be sure? I am thinking out of time, bad coils, all four 02 sensors need to be replaced, or cats are clogged. More of the cats and coils. Normally the driver side coil goes first.

Ken2012

Thanks for the following advice on my "popping" and "shaking" 1994 SC400:

"I am thinking out of time, bad coils, all four 02 sensors need to be replaced, or cats are clogged. Normally the driver side coil goes first."

Also, cranks over in a second or two on the first start of the day; then the subsequent starts are quick, no delay, following the first start.

The SC starts out with no popping or shaking until after warm-up; would pass a test drive. The problems begin in 15-20 minutes after driving the car.

I'll keep you posted on any results in the next few weeks.

Ken2012

My experience with the SC400 this last year is complicated by the technology, and terminoloy, i.e., the following recommendations:

Check all of these....

Check then recheck..

MAF
IACV
TPS
all four 02 sensors
plugs
wires
caps
rotors
coils
then check the timing
bad ecu

the first thing I would do is the fuel ecu mod, its cheap, fast, and could immediately fix your issues....

The problems were not completely diagnosed since the scan tool wasn't communicating with the ECM; the EGR system was not operating and was completely replaced; the motor mounts were also collapsed.

I haven't replaced the ECM or the motor mounts yet; the ECM was quoted between $1,500-$3,000, so the motor mounts may be the next project for next year.

Thanks for all the information; the results of the next maintenance will be reported; hope this helps.

92sc400dd

I too am having a similar issue. My car is a 1992 SC400 and it idles rough and all over the place. Will not take throttle past 25% or so. And now backfires will driving after my most recent fill up. Very annoying happening and I hope someone can help me before I pull out the last strand of hair I have.

No check engine light at all. Jumpered the pins and light flashes at me as if calling me stupid.

Ali SC3

iTrader: (10)

I got flamed for this one a while back there is no timing adjustment on the 400.
only engine you can adjust the timing via the distributor is the 2jz-ge.

I think you have a bad coilpack.

you can get a used ecu for a few hundred from our vendors. a new ecu would be a waste really just get a known working one.
Were they using the right scanner, if it is odb1, you have to use the special toyota scanner even then it can be "iffy". the true test is if your cel works and lets you pull codes or just blinks constantly (what it does if there are no codes). If it does not light up at all or is erratic, then bad ecu may be a possibility.

On an SC4 we get these threads all the time, statistically speaking if it is not the fuel pump ecu it is usually an ignition problem

well that means the light is working, there are just no codes. I would check the 2 coils, the rotors on each distributor, and then maybe the TPS especially if it has been changed recently.

go through the steps in the general SC4 problem thread.
I would disconnect one of the coils (safely) and see if anything changes. if it doesn't change thats good because you will have found your issue.

Bankswood

You do set the timing on the 400. It's done by setting the timing marks on the cams to 10 o'clock and two o'clock.

Ali SC3

iTrader: (10)

I said there is no timing adjustment, as in you cannot just simply turn the distributors like on a 2jzge.
I think the OP would know if the removed the timing belt recently and if thats the case then the timing could be off but sounds like he just changed the plugs and wires.

maybe check all the plug wires are going to the right spots it can be tricky they cross over and stuff.