LS4forME

Okay this problem has been on going on my LS for...well i lost count because its been that long.

Problem -

Car can't idle. When you come to a stop or under 10mph and not giving the car ANY gas, even a slight step on the pedal, the RPMs will just drop and the car will die. ON gas, the car drives normal and can make it home if there is not stop and go...basically can't come to a stop and idle.

What I noticed -

This problem ONLY happens 10-15% of the time I drive the car..so its random and unexpecting

Also, I noticed it happened more when it was raining rather than dry weather conditions.

only has this problem at operating temperature, never when cold or warm.

when car DOESNT have this problem and comes to a stop, it has a low idle, maybe 400-450rpms and the needle on the tach is very shaky.. hard to explain. The needle vibrates as it has a slight rough idle like its having a hard time to idle till gas applied.

when driving with no problems and coming to a stop..i notice the RPM needle dip down to 400rpms before a complete stop and something adjusts and brings the idle back up to around 1000rpms then back to 400-500rpms when the car eventually reaches a complete stop and just sits there.

when the car dies, i can start it right back up with NO issues and it just dies again if not applying gas


What i know about the car -

1990 ls400
240+ miles
cracked intake pipe, fixed with silicone but i doubt its 100% sealed.
EGR tube is cracked

help help help..im stumped...car drives fine and wish it could be reliable as the old days. Car runs perfectly when these issues aren't happening..

I know its a handfull to read but let me know what you guys think

Thanks

omarg

my car did the same thing, exactly. I was going to replace the tps (throttle position sensor) but just took it off, blew the dust off of it, reinstalled.

has not happened again in over 20k miles.

try it!

LS4forME

I knew it was a simple fix!! ill try it today and let you guys know the outcome

steve2006

If you remove the TPS ensure you mark the original position so it goes back in exactly the same place or it will need setting back up again.

Look below for details

http://www.lexls.com/tutorials/EFI/tps.html

There are 2 other possibles for the idle fault one is the throttle body itself gummed up which needs cleaning.

Look at link below for details

http://www.lexls.com/tutorials/EFI/throttlebody.html

The other possibility is the ICV ( idle control valve)

LS4forME

Im going to do these in order to see if it fixes the problem

1) Clean and Adjust TPS
2) Replace TPS
3) Clean Throttle Body
4) Check/clean/replace ICV

Amskeptic

Add "carefully inspect the breather hose from valve cover to throttle body with a bright light and a mirror."
Colin

LS4forME

how is this done?

thadword

I went through that too w/ my '92 ls4. What I did was focus just on Shell premium gas. That helped alot. Watch the gas you're putting in there. It would help to repair the cracked intake pipe properly, and the EGR tube. Also, have your fuel system, fuel injectors, and mass air flow sensor checked. Did you have a major tune-up? Make sure you have a trusted, well-qualified mechanic. Follow through with the other good advice on here and you'll be fine. Treat this car right and it will treat you right.

Garage7RP

iTrader: (1)

Check all of the intake hoses for leaks or cracks and repair or replace as needed. Is the check engine light on?

LS4forME

no check engine light but sometimes the trac light and check engine light come on at the same time and turn off at the same time. This happens like 50% of the time when i drive the car but nothing happens to the car. It drives normal when it happens so i never really bothered.

Garage7RP

iTrader: (1)

Ok, some connections are loose by the way you described it. Before you installed your custom engine ground wires, were you already experiencing these problems?

PureDrifter

iTrader: (10)

check the trunk hinge.
http://www.lexls.com/tutorials/lighting/bulbout.html

LS4forME

yes I was. and i am sure the ground kit has nothing to do with these problems.

LS4forME

ive cleaned the TPS and no problems since..idle does dip down low sometimes(200-300rpms) but has not died on me since. I think my TPS is on its way out.