KJG92

Strangest thing going on with the 92 LS400. A few weeks back we got in the car and took it up to caffeine and octane north of Atlanta. Car did great as usual. We browsed around for 3 hours and got back in the car and it ran/idled like crap. Shut it off and started it back up and it just sputtered. We pulled out and within a half mile it smoothed out. But I noticed that when you let off the gas it jerked and when you would feather back into the gas it would jerk. The next morning it was fine. My son drove it to school and back and it was fine. A couple weeks later he drove to school, then to the store then crunk it back up and it ran like crap all the way home. It seems that if you start it then stop it then start it back up within a 6 hour period the car runs like garbage. I played with the TPS and couldn't get any change out of it so we replaced it and adjusted it per the second part of lexls website. Now it runs even better than before (on first start) and no jerky throttle. But now on the second start it shakes at 40mph around 1600 rpm then smooths out after that. And also has a semi rough idle. What is up with the 6 hours between starts that smooths it out and if you start it before that period that makes it run like crap? Lscowboy rebuilt the computer last year and we replaced all the vacuum lines on the top of the motor as well. CEL came on once but went back off after it sat and has yet to come back on. Even after this last stint with the new TPS. Kind of weird, seems like maybe the crank sensor and it resets after that long period of time and goes bad when it heats up maybe? I don't know. I do know that I don't want to throw parts at this car cause all these sensors are costly. Thanks for your time.

AandSC

When is the last time you replaced the fuel filter? If it were me I would start there. Could also be a gas cap issue, which is an inexpensive possible fix. I had to replace my gas cap about a year ago.....

KJG92

Went out and checked and the CEL was on. Got a code 25. A while ago we changed out the front O2 sensors, used Denso. New fuel filter went in around the same time as the O2's. The car is running rough right now. But in the morning it will be fine until you stop and turn it off and then start it again. It's just strange, cause it will sit for 6-8 hrs in the school parking lot and then be fine for the trip home.

I just went out and checked the gas cap. Wow at the pressure. And usually you'll get a little puff but this felt like it was going to blow the cap off in my hand and it went on and on. I started the car and could feel the pressure while it was running but the car still ran like crap so I put the cap back on. Seems like excessive pressure, none of my other cars do that.

deanshark

My 93 did that and my 94 does that. Both only when very close to empty. Thought I broke my wrist one time it blew off so hard. Ya need a new gasket for the gas cap. That shouldn't cause the car to not start though.

Banshee365

Wouldn't the fact that the system is holding so much pressure indicate the gas cap seal is holding pretty darn good?

deanshark

http://www.lexls.com/tutorials/maint...capgasket.html
Pretty sure it's supposed to release a little pressure. When my gas cap failed part of the Emissions test I finally changed the seal and it passed. Also never had the major pressure build up anymore.

Banshee365

Interesting. I don't know if that's a UCF10/11 thing or something but I haven't ran across that one yet. That's sure a far cry from the way cars are today.

KJG92

That is very interesting. I wonder if the excessive pressure messes with the fuel pump. I'm going to change that out and see what happens. Anyone have the ohms specs for the coolant temp sensor? I found the ones for the O2's.