sulliman

Hi as anyone any advice, my 98 ls400 idle r.p.m. has dropped to approximatly 400r.p.m. when stationary in drive.any help will be appreciated

SpencerT

welcome to the club!

400 is not that low though and is within the normal range.
If you really want to get into it, your throttle body would be the first place to check.
Clean the butterfly valve and go from there

Yamae

I had the same problem before with my Celsior. Cleaning the throttle body fixed it as well as the behavior of the car was quite improved. I mean the car accelerates smoothly after turning tight corners. I first thought it was a transmission problem before but it turned out be the clogged throttle body.

Before the cleaning I always had an unusual acceleration right after turning the tight corner. It seemed to be that there was no engagement of a gear and I used push the gas pedal more and then what happened was the suddenly acceleration. The problem has completely gone after the cleaning.

sulliman

Many thanks to SpencerT and Yamae I cleaned out the throttle body and butterfly valve with a recognised aerosol cleaner, although it has not altered the idle speed the engine appears to pick up more cleanly and is more responsive,I was advised at the shop to clean the E.G.R. valve,unfortunatly i am unable find this valve, but i am happy with the results from the clean throttle body. Many thanks

PureDrifter

iTrader: (10)

'98-00 don't have EGRs.

I hope you actually took the TB off and scrubbed the inside down with a toothbrush or something to remove the carbon, just spraying cleaner on it doesn't do a whole lot. Specifically there's a small plate on the top of it that comes off with 2 screws and contains a couple small passages that you'll be wanting to clean out.

xtremex626

iTrader: (3)

could be spark plugs.

SynicalVip

iTrader: (2)

Mine doing the same thing it idles at the 200-400 range when am in drive. I have clean the maf sensor and throttle body but still the same. It may be the spark plugs that I recently change not so long ago, although it was pre-gap but guess its not good still. At what gap should the spark plugs be?

Lavrishevo

iTrader: (1)

When you are looking down at the needle it can appear to be lower then it is. Try looking at the needle from a lower angle. Anything below 4 -5 hundred is not good on the car. There was a revision in the ECU that did increase idle in gear I believe.

PureDrifter

iTrader: (10)

oem spec is 650rpm +/-100rpm iirc, may have been 600.

LScowboyLS

I have had a low idle problem twice, the first time it was bad bearings in my Idle Air Control Valve (IACV)

the second time it was accompanied by a myriad of other issues and turned out to be bad ECU capacitors

if you used the correct NipponDenso or NGK plugs, then they are pre-gapped to the correct gap, which, as I recall, is 1.1mm on all LS400 year models.

PureDrifter

iTrader: (10)

'98-00 don't have IAC valves, and bad ecu caps are very unlikely (at least at this point in time) in '98-00 cars.

Spark plug gap SHOULDN'T be an issue on just a low-idle, but if the plugs are really old it's possible I guess.

OP, are you measuring with the engine warmed up and in NEUTRAL or in Drive?

cobalt91

Is it throttle by wire?

sulliman

Thanks to all for responding .hear is an heads up,the throttle body removed and cleaned also the small plate removed and the several small holes cleaned out , of which two where blocked.the spark plugs are new iridium tip N G K The air filter is K&N NEW ENGINE OIL 10/40 semi synthetic new transmission filter and the correct ASIAN oil. complete stainless cat back exaust with single resonater which also acts as a balance pipe,the duel system continues to a single power flow box on side. The car runs very well and sounds great, the milage 237800 as of today. I am wondering now if i have caused this idle issue with the changes from standard . Thanks again

PureDrifter

iTrader: (10)

my car's more modified than yours and still has a perfect idle. I ask again, are you measuring in drive or neutral, with AC on or off?

'98-00 are all Drive by Wire, but have a fail-safe throttle cable that only opens the throttle a small amount when the pedal is pushed all the way down.

timmy0tool

iTrader: (7)

i idle pretty low (according to the tach ~400rpm) as well but that's usually in drive. to my understanding this is normal and i have never stalled out.

never knew that! good to know.