Stuttering At Highway Speeds

[sanstoetter]

I have a 94' LS400 w/ 190,000 miless, and since I've owned the car its been flawless. Lately the car seems to stutter between speeds of 50-70mph, or under load around 45mph. The car seems to free rev smoothly, and pulls smooth if I run it WOT, so it seems like a partial throttle issue. With that in mind it seems like either a transmission issue, or maybe the TPS sensor on the fritz. My plan is to change out the trans. fluid and strainer soon, but I wanted to check on here first to see if anyones had this issue before... if so what was the underlying problem?

[Marklouis]

I have a 94' LS400 w/ 190,000 miless, and since I've owned the car its been flawless. Lately the car seems to stutter between speeds of 50-70mph, or under load around 45mph. The car seems to free rev smoothly, and pulls smooth if I run it WOT, so it seems like a partial throttle issue. With that in mind it seems like either a transmission issue, or maybe the TPS sensor on the fritz. My plan is to change out the trans. fluid and strainer soon, but I wanted to check on here first to see if anyones had this issue before... if so what was the underlying problem?

Have you already checked the Transmission mount to see if it needs replacing? that's a main contributer if your stutter seems like a vibration -

[sanstoetter]

I'll probably replace that while I'm working on the car, but I doubt it's a vibration from that. The car shudders noticeably, and it reminds me of a trans. trying to search for a gear. It also feels the same with O/D on and off at 55, and comes and goes kind of randomly. On steeper hills I've noticed it happening every time if I keep the car running a steady 45mph, and it happens every few seconds.

[Marklouis]

I'll probably replace that while I'm working on the car, but I doubt it's a vibration from that. The car shudders noticeably, and it reminds me of a trans. trying to search for a gear. It also feels the same with O/D on and off at 55, and comes and goes kind of randomly.

ok, now I see what you are saying. fluid and filter change wouldnt hurt anyways!

[landar]

I'll probably replace that while I'm working on the car, but I doubt it's a vibration from that. The car shudders noticeably, and it reminds me of a trans. trying to search for a gear. It also feels the same with O/D on and off at 55, and comes and goes kind of randomly. On steeper hills I've noticed it happening every time if I keep the car running a steady 45mph, and it happens every few seconds.

How does it perform on steeper hills at 45mph and locked in 3rd gear?

[SRK]

Part throttle misfire is very likely a bad ignition wire or a spark plug. Easy fix.

[killerFatty]

I had a very similar problem when I first got my car. It seemed to go away after I replaced the plugs and wires. I also used an excessive amount of sea-foam both through the gas and a vaccum line. That all seemed to clear it up. Another thing you might consider if you want your engine to run more smoothly is cleaning your throttle body. Mine idled and accelerated smoother afterwords.

[da_fugative_7]

I had a similar problem with this and I had the trans fluid changed, cleaned the throttle body, and used seafoam and it became a rocket...it would be a good idea to check your trans mounts as well...