LS400Mike

This is the second time I have done a starter on a 1990 lexus ls 400. Last time I did it the only problem I had after I put the intake back together was a small leak where the throttle body meets the upper intake manifold. This time after i finished I had a small fuel leak, a small coolant leak at the rear bridge (sucks), and the biggest problem is the idle. I fixed the coolant leak and the fuel leak, but the problem persists. It starts and runs fine, but the idle kicks back and forth between 600 and 1400 rpms. Like clockwork every two seconds it idles up and drops back down. My first thought is I have a leak in one of the gaskets in the upper or lower manifold. I can't really hear it to well, but I think I do hear a air leak noise(kinda like a soft whistle). I am not going to go into what a pain in the butt changing the starter is in this vehicle, but I thought this would be a good "brain-storming" post on some of the possible issues that can arise when changing the starter. Aside from the coolant and fuel leak I started with, I am getting pretty good at taking this engine apart lol. Remember, this problem only occurred after I replaced the starter and went through taking out all the vacuum hoses, air intake manifold, and all that comes with that mess

akitomk3

iTrader: (2)

How bout checking to see if everything is properly connected, i know you probably did it, but going over it slowly one more time isn't going to hurt. Is your TB sensor connected

LS400Mike

Sorry to post to my own thread, but I remebered that I cleaned the throttle body and intake manifold in a solvent tank this time. Didn't do that the first time I did this job. Is it possible I damaged the throttle body sensor with solvent. Just a thought. Not a professional mechanic, just a professional in general.

LS400Mike

I do have some vacuum issues. Always had them though, even before I had this issue. There is a small pea green vacuum device that sits over the return heater hose going from the block to the radiator. The ends broke off this years ago, and I have never been able to reconnect the vacuum hoses to it. One hose goes from the canister to this device and one from this device to the top of the throttle body. Every other vacuum hose is correctly connected (I went over the diagram on the hood thoroughly). I have tried plugging these hoses, but it doesn't seen to change the idle problem.

LS400Mike

Yes there are actually two sensors on the right side of the throttle body, and both have been plugged back in. I assume one is the TB position sensor, not sure what the other is.

LS400Mike

Problem solved!!!!

I started ripping the upper and lower manifold out and immediately found the problem. I had pinched a wiring harness between the upper and lower intake manifold. It was the small harness that came to the underside of the upper intake manifold. Now I am surprised it ran at all.

I am new to this website, but I am trying to answer to as many posts as I can give a good answer on. I know I am not the only one that put a starter in thier ls 400 and had some kind of issue when they put it back together. I didn't see a lot of other threads on the problems that might occur when you take on this project. I was kind of hoping this would help someone else. The best advice I can give to someone doing this project is to be very precise when saving the parts, and very careful and mindful when you remove and replace each part, nut, or bolt. Its not something you would enjoy doing twice. I have done this twice before, and still managed to make a silly mistake.