Rough idle

[Zafran]

A few days ago I was driving cane to a stop and all of a sudden my car began to shake slightly at idle. Lost the smooth Lexus feel :(. Nktice a lag in power when I put my foot down. 

Any suggestions on a potential fix.

 

I have a 96 ls400, filter and oil spark plugs cambelt water pump all changed by previous owner. 

[LenT]

1 hour ago, Zafran said:

A few days ago I was driving cane to a stop and all of a sudden my car began to shake slightly at idle. Lost the smooth Lexus feel :(. Nktice a lag in power when I put my foot down. 

Any suggestions on a potential fix.

 

I have a 96 ls400, filter and oil spark plugs cambelt water pump all changed by previous owner. 

I don’t know this model, but it does sound like you have a plug misfiring.  Now that could be the plug itself, or a loose plug lead or an ignition problem on one cylinder.

I would check the plugs and leads first, as being the simplest option - if they’re easily accessible.

[Malc]

10 hours ago, Zafran said:

I have a 96 ls400, filter and oil spark plugs cambelt water pump all changed by previous owner. 

but when ?  and how was your test drive before you bought the car ?

I've never experienced your symptoms in my 95 Ls400

Malc

[Spock66]

9 hours ago, LenT said:

I don’t know this model, but it does sound like you have a plug misfiring.  Now that could be the plug itself, or a loose plug lead or an ignition problem on one cylinder.

Yes does sound like a misfire, could also be a faulty injector.

[Zafran]

9 minutes ago, Spock66 said:

Yes does sound like a misfire, could also be a faulty injector.

I have no lights on the dash, surely if this was an issue. It should pop up on my dash?? 

[Spock66]

1 minute ago, Zafran said:

I have no lights on the dash, surely if this was an issue. It should pop up on my dash?? 

Possibly, but if it's an intermittent issue you may not.  The on board diagnostics of modern cars are pretty good, but as your car is earlier the diagnostics are probably less sophisticated.

Certainly excessive vibrations are a likely indication that one cylinder is not firing, so going back to basics either there is no fuel/air mix, no spark or no compression.

[Malc]

thinking differently here ....  in times past ( on this forum )  some vibrations due to propshaft imbalance at some speeds / idle ...  what's your mileage ?

Malc

[Zafran]

40 minutes ago, Malc said:

thinking differently here ....  in times past ( on this forum )  some vibrations due to propshaft imbalance at some speeds / idle ...  what's your mileage ?

Malc

Mileage is only 95k. Could this be a dirty throttle body? 

[runsgrateasanut]

Check your vacuum lines. I've known the plastic tube that enters the Plastic pre joining the Throttle body to snap off which will affect your fuel mix beyond the MAF sensor.  Can't recall exactly what this did when I discovered this partial break, but ??? Also sticking ICV perhaps?

[Spacewagon52]

2 hours ago, Zafran said:

Mileage is only 95k. Could this be a dirty throttle body? 

I have read on this forum a few issues with the throttle body. Once cleaned the issue seems to be cured. Somewhere on here there is a thread on how to clean the throttle body.

[Malc]

3 hours ago, Zafran said:

Mileage is only 95k

this is a tiny mileage for any Ls400  

Malc

[Zafran]

12 minutes ago, Malc said:

this is a tiny mileage for any Ls400  

Malc

Hahha yep, I'm very lucky 😉 , but here I am with a few issues lol. Thank you all for the help so far!!

[Zafran]

20 minutes ago, Spacewagon52 said:

I have read on this forum a few issues with the throttle body. Once cleaned the issue seems to be cured. Somewhere on here there is a thread on how to clean the throttle body.

Yep I have seen a few on here, going to attempt that first. I've tried injector cleaner also, that didn't really resolve the issue. 

[Zafran]

If you look at the connection above the belt almost seems bent back on itself. I'm curious to know what that is for anyway. 

 

 

 

[steve2006]

I can’t be 100% sure if that is the cam sensor or the suppressor capacitor connector, just have a look in the black sleeving circled to see if there is just one wire in there.

Looks like the ignition leads are still original so chances are so are the distributor caps and rotor arms which could be the cause.

No fault codes will be shown for ignition faults on this model.

You need to determine whether the issue is fuel related  (throttle body, injectors or vacuum leaks) or ignition related as above.

 

 

[Zafran]

Thanks my plan of action is similar to as you described,

 

Fuel Injectors - Using additive cleaner 

Throttle Body - Clean 

Then moving onto the distributor caps and rotor arms.

Thanks all this has been helpful I will keep you all informed on the progress  

[Cotswold Pete]

One other thought, not that I have had this on lexus, but on other cars have had lumpy engine at speed and idle.

The petrol filler cap, which if the seal has gone might be a problem.  It is highly unlikely but worth a check.

My money would be on leads or distributor playing up.

 

[shanra]

I had very similar problem and it was fixed by replacing the temperature control sensor.

 

[runsgrateasanut]

I was trying to figure out where this particular vacuum leak is positioned?  Not my photo .

[steve2006]

They look like the ones that run around the plenum chamber ( the bit which has the Lexus symbol on it).

Picture shows all the vacuum pipes except for the brake servo vacuum line and the two bigger pipes from the air intake pipe work between the MAF and TB.