jserman

So I picked up a 91 LS400 about 2 weeks ago... car runs great has some small issues but nothing that can't be fixed....

car has a little over 175K miles on it..

so the other day I pulled up to a light and while sitting there the car started ti stumble/shudder.... not bad just small noticeable... you can see the RPM gauge fluctuating from 600rpm then drops for a sec then back up....

if I put the car in N it idles back up and doesn't do it..... but if the idle drops down around 800 it does it sometimes....but seems more prevalent under a load..

It does with with the AC on and OFF... and sometimes doesn't do it at all...

I have changed the oil and trans fluid since I got the car but nothing else.. also I am not getting any CEL's

any ideas on what to look for... I am confused on which way to go... sometimes I think it could be the trany then other times I think its the motor...

I am lost

onelove316

first trying cleaning out the throttle and the idle air control valve those do just what you are talking about if they are dirty get some throttle body cleaner first and clean it out really good then put it back together and take it for a run and see what happens if it still does it come back and take the idle air control valve off and clean that should take care of it , if it was the transmission you would know it because it would do it all the time when you are driving not just sitting there idling let me know how it goes.

jserman

^^^ my thoughts exactly but just wanted to make sure... I think the Idle air control valve was replaced by previous owner but of course I can't find the paper work... I plan on doing an upper engine clean on it this week... then go from there...the guy I bought it from was an older gentleman so I am sure he never got on it so might just need to romping on to clean the motor out.....

I just wanted to make sure I wasn't missing anything...

jserman

I haven't had a chance to mess with this... I did notice the coilant was low so I topped that off... and I pulled and cleaned the maf... seemed to make a little diff nothing major...

last night I did an ECU reset by puling the EFI fuse... went for a spin today seems to be running better.....I still plan on doing an upper engine clean here ASAP and i think that should cure all...

hobojoe

look at my post i have going 91ls dying at lights i think we are having almost the same problem....

EXE.UCF10

iTrader: (3)

When was the last time your spark plug wires, caps and rotors were replaced?

damon

I have the sympotms along with a CEL (code 25,26) & am trying to alleviate with new coils & 2 new O2 sensors. 94 LS

jserman

yea i read yours.... doesn't seem to be the same... cause yours happens when its hot or something right??? mine did it all the time

I don't know... I just bought the car... have been thinking about that stuff but wanted to go cheapest stuff first

I wish I was getting a CEL that would make things easier....

damon

New coils & O2 sensors did the trick for me.
O2 sensors alone took care of my 25,26 CEL.

python

iTrader: (4)

NEW COILS! nice one damon... ill bet if u put some octane boost or injector cleaner in it smooths out...ohm them out and ill bet u find the secondary part of the coil(s) to be bad

jserman

well I did an upper engine clean on the car.....not much seemed to come out the back so we will see... problem doesn't seem as bad as it first was...next step is to clean the TB I just need to order the gasket first.....

python

iTrader: (4)

did u ohm the coils out?

jserman

what coils??? explain....

python

iTrader: (4)

uhhh ignition coils.....

jserman

doesn't the car have a cap and rotor??? i have only seen 1 coil....