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Typical New Guy Question


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First, I want to say thanks for all the help you all have provided via a little thing called “search”.

First, a little history on my 1993 LS400. A fellow employee gave me the car 3 weeks ago after it sat in his driveway for two years. He said it suddenly starting running rough like it was only running on 4 cylinders. He said he had replaced the plugs, wires, fuel filter and cleaned the injectors. His mechanic told him it might be the timing belt. After hearing how much it would cost he just bought a new Avalon.

I took the car…did a few internet searches and bought a coil. It now felt like an 8 cylinder, but it still had a miss in the idle and the smell of gas at the tailpipe. I checked the plugs they looked good. Wires appeared new. I replaced the other coil and the ECT sensor (it was a freebie, so I figured, WTH). The car ran lot better but still had the same problems. I finally pulled the rotors and found one was cracked in 2 places. Replaced both caps and rotors…Great power after the off idle stumble but, NO CHANGE in sitting idle quality!

My question is…

So…Where do I go from here?

I probably should have cleaned the IAC and the Throttle Body when I tore it down on one of the previous times. Guess I should have read more…Is there anything I am missing topside.

For an (almost) free LEXUS with 127,430 miles on it I think it is worth a HARD LOOK. The interior and the exterior are in good shape. It has the LS400 dash flicker but you guys have already told me how to fix that. The original timing belt was replaced at 76,000 miles. The air suspension was replaced at 115K. Any help would be appreciated. Thanks again.

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Most common idle problem is IACV dirty/sticking and/or dirty throttle body. It sounds like doing these is well within your grasp. Its a good general maintenance items so you won't be wasting your time even if it isn't the problem. Some guys clean throttle body on the car. I guess I feel you get a better job if you remove it. A bit more work but lets you get it equally clean on both side of the valve plate.

Other than those more likely factors it could be a manifold leak caused by loose or ill fitting ductwork, a detached vacuum line, a cracked vacuum hose somewhere. Lastly it could be a dirty MAF but I'd rule out everything else before messing around with the MAF.

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Propane is probably easiest but of course be careful. Just a trickle out should do it. You don't need to dump full open torch gas flow. Of course do this outside, not in the garage. Propane is heavier than air so it sinks to the ground. This is why propane is more dangerous than natural gas. Natural gas floats away, propane collects in low lying spots.

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I cleaned the TB and the IAC...Man you talk about coaked.

I am surprised that the throttle body worked at all.

IAC was nasty as well. Seems to be running better, but the miss is still there.

The only thing left is to start looking for vacuum leaks I guess.

Someone mentioned fuel filter but I was told that it had already been replaced. Could a fuel filter or an O2 sensor cause this kind of problem?

I am at a loss.

It is hard to believe it is this difficult to track down something as evident as this miss is. When things happen intermittently it makes sense NOT to be able to find a solution. But this miss is like sitting in my face laughing at me. VERY AGGRAVATING! that that meltdown is over I can start looking for vacuum leaks.

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#3 plug wire arcing. New plug wires my a$$. :censored:

Ordered new OEM wires and plugs.

Sometimes in our darkest moments we need to stop and accept our own limitations.

I had someone else look at the car.

Didn't tell him what I had done.

Took all of about 30 minutes for him to locate the problem.

Never been so UPSET and HAPPY at the same time in all my years.

From what I had been told the wires were replaced as part of a tune up

in an attempt to solve what turned out to be the bad coil.

Which turned out to be the reason I was given the car in the first place.

The wires looked perfect until he started scoping them.

Replace that one wire now it runs smooth as silk...Truly Amazing.

curiousB...just wanted to say thanks.

Now its time to try soldering...Look out instrument cluster here I come.

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Thats a good suggestion when you run out of ideas. Don't tell the new guy coming in all your theories so he comes at it with a fresh set of ideas.

Glad to hear you're back and running.

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