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92 Sc400 Hesitation


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Hi, my 92 SC400 has a light amount of hesitation - and here are the conditions when it occurs:

1. Around 50 - 100 mph and medium acceleration.

2. More noticeable in overdrive gear and not noticed when revving harder in 3rd gear.

3. Moreso when the car is warm and less when cold.

4. Fuel economy is not affected... not yet at least.

Here is what I've done:

1. Plugs are less than 2 yrs old - so I pulled each and checked for carbon build up etc..

2. Wires are less than 2 yrs old - so I've checked them to be ok.

3. Changed both rotors and caps, thought this was going to solve it but - nope.

4. I've been putting premium fuel (and an injector cleaner bottle).

** Here's an interesting thing I did notice. When removing the driver side cap, I looked closely inside the middle contact on the side where the wire is plugged in. This is the wire from the coil...- well it look dis-integrated from tiny arcing or something. This is what led me to replace the caps but the hesitation still persisted. Now the cap on the other side wasn't like this one and I was wondering if I need to work backward on the driver side electrical system - ie. the coil. Is it possible for the coil to have hiccups randomly and cause arcing at the wire or when coils die - do they just die completely. With the new cap in I've been checking every so often to see if the same phenomenon takes place but it's been a month now and now signs - so I'm just living with this annoying hesitation.

thanks for any ideas!

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Hi, I had the same problem as you do and as many others on the forum have had, I did everything to try and cure it that people on here have done, ie....plugs, wires, distributor caps and rotors, clean throttle body, clean mass air flow (even had a code showing mass air flow was bad so changed it out...no change), and more.....but still had the same idle problem, hesitation and sounded like I had a race cam installed. I finally found out what the problem was......check your idle air control valve...it is what controls the vacuum for your engine....it is on the front of your V8 right under the plastic housing for your plug wires, it is round and has vacuum lines running to it as well as lines for coolant. I think it is an $800 part from Lexus, the Mass Air Flow Meter is $1600. It's easier to pull the whole assembly off the motor and then disassemble it once you have it out as the screws holding it together are easy to strip out...once off the engine you will notice a rod that should move in and out as it spins which adjusts the amount of vacuum your engine needs....it will probably be stuck in the full open position as mine was due to carbon build up...take the three screws out holding the assembly together and then with carburetor cleaner clean it until the rod moves freely....it has spring tension so that it can spin in and out, once cleaned and moving freely then check where it was mounted to the engine and make sure the inlet is cleaned and not clogged with carbon...then reassemble unit, remount on engine and it's also a good idea to pull your negative cable on the battery to reset your computer. Once that is done then start your new smooth running Lexus V8 up......Mine was hard to start and keep running after the cleaning, don't know if someone had adjusted the idle on it in the past or what but I had to adjust the idle screw a bit and once that was done it idles at about 600rpm when warm. Just like everyone else on here I pulled most of my hair out trying to figure this one out..... hope this helps. I bought my 92 Lexus SC400 about 2 months ago and love it now that the idle problem is solved.

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Well I've check the driver side coil resistances,

connector pin spec is 0.4 to 0.5 ohm, and I checked numerous times only to get 0.7 ohm - OUT OF SPEC

+ve connector to plug wire spec is 10Kohm to 14Kohm, and I got 13.3Kohm - HIGH END OF SPEC

Could this be the cause of my slight hesitation ? Car starts very good and only has intermittent hesitation at highway speeds ...

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