Hi all:
I've just joined the forum and hope that someone can give some insight onto the problem I'm having. I have a 91 LS400, 180K
When the throttle is just feathered, the car stumbles (speeds above 40 are most noticeable). When I take it out of overdrive, the same symptoms occur at higher RPMs, but the same feathered throttle, so it doesn't seem to be RPM related, but more due to the throttle. When the throttle is pressed harder, normal acceleration (disclaimer: not having driven another LS400, I can't be sure that the acceleration is as it should be - how to check?). Items replaced or changed so far:
Timing belt - partially corrected the problem (old belt had jumped a tooth or two), needed anyway since it appears that it had the original timing belt with 170K miles on it!!
New plugs, plug wires, distributor caps & rotors, air filter
New Throttle Position Sensor - no change
Hacked fuel pump relay to deliver constant 12 V to fuel pump (partially corrected the issue)
New fuel filter
Other:
No Check Engine Light codes.
15-17 MPG mix of freeway and city.
Just barely passed smog last inspection.
I've been considering replacing the fuel pump next, but am at somewhat of a loss as to what the symptoms indicate. Any suggestions?
Jim
91 LS400