91 Ls Engine Sputtering, No Power Problem

[488civ10]

LOC guys/gals,

i have a weird engine sputtering/ stalling problem that is intermittent (as in almost a year apart). it happened once last summer while my wife was driving it, then it went away. happened to me once in february 2010, but i put it into neutral, gave it some gas and the rpms roared and the problem was gone. my dad borrowed it last month, it sputtered again, with the rpms going from idling speed to almost stalling a few times, before it died completely. this problem was repeatable, and after he restarted the car, it did the same thing three times. so i had it flatbedded to my mechanic, and of course... he was not able to replicate the problem.

yesterday, it was a pretty hot day, and with the a/c blowing and on my last stop of the day, getting ready to head home it finally happened again. when i step on the gas pedal, it doesn't do anything while it's doing the sputtering, stalling thing. i fully floored the pedal several times and still no response. i then popped open the hood to take a look at the engine as it was doing this (and tried slapping the IAC valve just in case), and saw the entire engine shaking and shuddering a lot. any idea what it might be? i searched the forums and read up on a ton of stuff, but nothing definitive, and no one usually posted follow-ups if/when the problem was solved.

MAF, IAC, fuel pumps, coils, distributors? i had the distributor, cap, plugs and wires all changed in january (and took a problem-free road trip to san francisco, averaging 26mpg with the a/c on the whole time, going 80mph). being that i'm not very mechanically inclined past oil, trans/diff fluid changes, i'm worthless in the DIY department. i used to go to a former lexus tech who went independent, but his quality of work, service and honesty has gone to total crap. he said he couldn't figure my problem and couldn't get the problem to reappear. i don't believe he tried much, if at all given the mileage from the time of the flatbed tow to when i got the car back was exactly the same. speaking of which, i should check the MAF. i have a K&N, and i'm careful during the recharge/oil process. my former mechanic recharged it for me, and given his recent track record, perhaps he doused it with oil. anyway, any help/suggestions would be welcome. just want to have an educated stance before i call two local mechanics that have come highly recommended by two of my friends.

cheers,

488civ10

[97CE LS400]

Poss. coils

[curiousB]

Poss. coils

A stuck IACV would only be a problem at idle (erratic idle). Since you see problem at many throttle positions it must be elsewhere.

It can only be fuel or spark.

Obvious fuel issues are a bad tank of gas, intermittent fuel pump or pressure regulator, or clogged injectors.

Spark issues are shorting wires to chassis, bad wires, bad coil, ecu issues....

Hard to prescribe anything very specific until you replicate the problem and diagnose it more.

Could also be bad coolant temperture sensor which may be sending ECU wrong signal.

[488civ10]

I appreciate the suggestions and help.

As far as the IACV goes, as I understand your comment, it should be that once I give it gas, the problem should go away, correct?

Poss. coils

A stuck IACV would only be a problem at idle (erratic idle). Since you see problem at many throttle positions it must be elsewhere.

It can only be fuel or spark.

Obvious fuel issues are a bad tank of gas, intermittent fuel pump or pressure regulator, or clogged injectors.

Spark issues are shorting wires to chassis, bad wires, bad coil, ecu issues....

Hard to prescribe anything very specific until you replicate the problem and diagnose it more.

Could also be bad coolant temperture sensor which may be sending ECU wrong signal.

[curiousB]

yes, IACV is just to maintain a constant idle speed when throttle plate is closed. Once you press gas peddle air leakage by throttle plate swamps the leakage through the IACV so it becomes irrelevant. If you only had erratic idle it might be worth focusing on IACV but that doesn't seem to be your symptoms.

[charlesranderson]

I periodically had this problem for about 2 years on my 91 LS400. Started when it got hot--rush hour traffic on the freeway with a/c running for extended periods. It was fine after it cooled down. Then reappeared a few months later. Tried a number of things--finally, certified Lexus Mechanic replaced the fuel pump--no problems since then.

[VBdenny]

Simple things first. Go to your favorite auto parts store and buy 2 containers of Complete Fuel System Cleaner. I have used both Slick 50 and Valvoline which both worked great. In some stores it is difficult to find but look for one that is at least $10. Dump both in and fill up the tank with top-tier premium. Before you go start changing expensive stuff, try this.

My friend had a Cadillac that did the same thing. The dealer changed plugs, wires, distributor caps and even the computer. Nothing worked and the problem continued. So one day I am riding with him (I sold real estate at the time) and he asked me what I thought he should do. I told him I thought we should drive right over to an auto parts store where I double dosed the Caddy. Within a few days it was running better. He was amazed, the dealer was probably *BLEEP*ed.

Simple (and cheap)things first.

[VBdenny]

lol

[fiveofakind]

I have had this same problem ongoing for the last 3 or 4 years. I guess I need to bite the bullet & replaced the fuel pump to see if that will fix the problem...internal fuel...ouch.....