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Ronstang

92 Ls400 Rough Idle After Replacing Starter

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This car has been sitting since Feb 09 because of this issue. One morning it would not start when I was leaving for work and it turned out to be the starter. The car has ~130K miles on it. Since I fixed the starter the car does not run properly. It has had a rough idle/misfire since I put it back together. The engine just shakes like 1 or 2 spark plugs are disconnected....even though that is not the problem. The car also stuttered and bucked at constant speed when driving. I will list all the things I have done to try and correct this problem to simplify this post. I really need to get this car running as we are down to one car and cannot afford a replacement at the moment.

The one constant in this scenario is the problem. It has stayed the same no matter what I have done/replaced so it is unlikely that the repairs I did along the way are at issue.

- Many of the wiring plugs on the injectors broke taking the car apart so I had to order new ones and replace them all. They were soldered and I used heat shrink and seal on all wires. I have verified that all are wired correctly and all are firing with full voltage at the proper time so I have ruled out my wiring job as the source of my problem.

- One of the first problems I identified was the injector seals were bad and no longer sealed after the initial tear down. Some were leaking rather badly so I assumed that was my problem. I ordered new seals and got new pintle caps for the injectors. After taking the intake manifold off a second time and installing the seals the problem remained.

- At this stage I moved on to the spark plugs/wires/caps/rotors. I could not verify the original equipment was functioning properly and some of the wires were out of spec with too much resistance. I decided to do the timing belt at the same time replacing the water pump and all the idler pulleys at the same time. I also did the valve cover gaskets since they were leaking and I thought that could be contributing to the rough idle as the plugs and wire ends were in a pool of oil....this issue cause a rough idle on my 93 Taurus SHO. The plugs were changed and all new wires and caps and rotors were changed. I used the good stuff, not the cheap junk. The problem still remained. I triple checked and the timing belt is definitely installed correctly.

- I then determined that I somehow had a vacuum leak. That explained the stuttering and bucking at constant speed so I figured I somehow messed up installing the intake. The perplexing part was how I did it twice. Turned out these cars have junk for intake manifolds and they tend to warp when you take them apart. I found the spec for out of tolerance in one of the books at the Lexus dealer. The intake halves did not sit flat with each other either. Luckily I have access to a machine shop so I used a fly cutter and slightly milled the mating surfaces of both halves of the intake. Upon putting the car back together it still had a rough idle but the stuttering and bucking was now gone. At least one of the problems has been solved.

- I have verified that all the injectors are working correctly. I had them tested on a flow bench and all are the same with a nice pattern.

- I borrowed a new coil from my buddy who has a repair shop and I tried it on both sides and the problem persists so neither coil is bad.

- I blocked off the EGR system since they can create a vacuum leak. The problem persists.

It seems to be an electrical issue but I cannot locate it. I have two ignition modules sitting on my work bench which I got out of a car at the junk yard. I figured I would trade them out to see if that might be the issue but I wonder how that could be the problem after simply replacing the starter.

I am baffled here and could really use some insight. Is there a possibility something is wrong with the cam or crank position sensors? If so is there a testing procedure? Could disturbing the wiring harness that have caused an issue I am missing? Any help would be greatly appreciated as I really need to get this car back on the road.

Thanks,

Ron

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I see you posted the exact same issue over on Club Lexus. Kind of a parallel approach of attacking the problem? (I see that often).

Some things I personally would try:

1) see if you can "pull" any codes from the OBD system. Know how to do that? -> http://www.lexls.com/tutorials/intro/codereading.html

2) take a sharp pick and systematically short(to ground) each plug wire, one at a time, to see if one makes NO difference. Old trick but effective.

3) while idling, spray some starter fluid into the air cleaner and see if there is any noticeable change in the way it runs.

I think you know where I am heading with each one of those "tests". Report back with the results and we can go from there.

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There are no codes. Not now that I fixed the vacuum leak at the intake manifold anyway.

The rest of the tests will have to wait til sometime this week as I ran out of time today and I have a busy few days since this is a short week.

Thanks

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My bet is vacuum leak when you replaced the intake manifold. Did you use a new gasket? Proper torquing instructions? Cleaned mating surfaces before you reinstalled?

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My bet is vacuum leak when you replaced the intake manifold. Did you use a new gasket? Proper torquing instructions? Cleaned mating surfaces before you reinstalled?

I have used new gaskets all the times I have had the intake off. I did have a vacuum leak between the lower and upper intake because they are junk and warp. Lexus even lists a spec for allowed warpage. I fixed the problem by milling both surfaces. The Lexus manual doesn't even list a torque sequence so I just worked my way criss cross from the center out in small increments to the proper torque spec. I just can't see there being a leak at the intake. I have also had the intake off about 4 or 5 times and each time it is replaced the problem is exactly the same. It is not likely that if it is a vacuum leak it is the manifold itself....although I am beginning to think it is a vacuum leak.

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Poor idle is a symptom of vacuum leak. Are you sure you milled it parallel to mating surface? You milled both surfaces? Depending on how much you took off it might not mate properly now (sits too low). Maybe angle of faces has been compromised and while maybe "true" isn't at right angle between the faces anymore.

Here is a simple test. Do this outdoors! Be careful! Get a propane torch and turn on gas to come out slowly, don't light torch. Run tip of torch around the mating surfaces. If engine revs up as you pass a spot there is a leak there because the propane being drawn into leak is making fuel mix more rich. Be careful. Do this outdoors....

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I will test again using propane just to make sure, I already did it once before. I am very confident that I milled the manifold correctly....I did it myself. Both surfaces are very flat and they mate properly now. Once again, the idle problem is EXACTLY the same as it was the first time I put the car back together so if there was no change after I milled the manifold I have to assume I did not add to the issue. I did cure the bucking and stumbling when I milled the intake and it no longer throws codes so I seem to be moving in the right direction. I also am very anal about my gasket mating surfaces. I do not use those scotch brite pads I see so many mechanics use. I prefer razor blades and a little bit of emery cloth on a block if needed.

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