Idle Rpm's

[mobilyte]

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[blake918]

I don't have any repair suggestionsl, but I can feel your pain...my '95 has a crazy low idle(in P and D4) when the a/c is off. It goes down under 500rpms, and hangs in the 400 range. The engine is perfectly 100% smooth even at that rediculous idle. However, when I turn the a/c on, the idle goes back to where it's supposed to be ~700rpms. The repair manual says the idle should be 650 +/-50. Here's a pic from a traffic jam the other day-I had the windows down because we actually had a nice day for once--a/c is off...

[92Lex]

I don't have any repair suggestionsl, but I can feel your pain...my '95 has a crazy low idle(in P and D4) when the a/c is off. It goes down under 500rpms, and hangs in the 400 range. The engine is perfectly 100% smooth even at that rediculous idle. However, when I turn the a/c on, the idle goes back to where it's supposed to be ~700rpms. The repair manual says the idle should be 650 +/-50. Here's a pic from a traffic jam the other day-I had the windows down because we actually had a nice day for once--a/c is off...

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Have you tried adjusting the throttle position sensor? The reason your idle goes up to 700 rpm's once you turn the a/c on is because your idle air control valve compensates for the a/c being on to keep it from stalling.

ever since i did my tune-up last spring, i noticed that it takes much longer for the idle rpm's to drop down to the 550-650 range. i had read that a dirty throttle body can cause this, but mine was clean even after 150K miles. anybody have any comments/ideas?

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From a cold start? Could be your O2 sensors not heating up fast enough so your car just takes a little longer to enter closed loop....it's no big deal though.

[Lexls]

Did you take the throttle body completely off? When I did my throttle body cleaning it looked fine....until I took it off...let's just say it was slightly dirty! I had to take a screwdriver to get all the crust off, the cleaner was no use when it's that built up.

Here's the side you can see when the throttle body is still on the engine...

And here's the other side of that...that build up is about 1-2mm thick!

More info on that here: http://www.lexls.com/throttlebody.html

Blake, it's sounds like you need to adjust your TP sensor as 92Lex pointed out. Your idle is really low and it can easily be adjusted back to normal.

[Jacob]

I’m also having a low idle problem (intermittent), and looking at these pictures makes me determined to clean my throttle body.

Jacob

[mobilyte]

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[92Lex]

Maybe just the heating element of the sensor. I wouldn't condem the O2 sensor as being the reason your car takes a little longer to reach a low idle...just a possibility. It's hard to say for sure unless you're actually able to hook up a DVOM to it and check it out for yourself. It would be a good idea to check those though...they'll go bad sooner or later.

[silvermate]

I’m also having a low idle problem (intermittent), and looking at these pictures makes me determined to clean my throttle body.

if its inermittent......or if the idle raises and lowers intermittently, its quite possible that you have a vaccumm leak somewhere..ie......cracked vaccuum hose....or a hose could be not connected tightly or even could be disconnected........just take a look and see ;)

[Jacob]

silvermate,

I have two problems: the check engine light and the low idle speed. Here’s a list of the parts that I’ve replaced so far to solve the problem:

Spark plugs

Spark plug wires

Caps and rotors

Oxygen sensors (Denso OE style)

PCV valve

Air intake hose

I also checked the hoses at the top of the engine and they all looked fine (I’m not sure if there are other places that I should check). Also, when I rev the engine I can hear a suction sound. So, does this combination of check engine light, low idle speed, and suction sound make you think of a possible cause?

Any help is highly appreciated.

Jacob

[silvermate]

silvermate,

I have two problems: the check engine light and the low idle speed. Here’s a list of the parts that I’ve replaced so far to solve the problem:

Spark plugs

Spark plug wires

Caps and rotors

Oxygen sensors (Denso OE style)

PCV valve

Air intake hose

that is an exellent start.......you did it right with all of that, you have yourself pretty much a full tune up......so thats good.....the car should run great after that.

I also checked the hoses at the top of the engine and they all looked fine (I’m not sure if there are other places that I should check). Also, when I rev the engine I can hear a suction sound. So, does this combination of check engine light, low idle speed, and suction sound make you think of a possible cause?

Any help is highly appreciated.

Jacob

check the hoses that are by the "L" emblem on the top of the engine. (i don't remember the actual hose off hand <_< )

check all hoses on your intake tubing all the way up the throttle body.....that sucking sound you are hearing sounds like a leak in the intake somewhere....you said you replaced the tubing........was that from the MAF all the way up to TB?

check for cracks in the tubing and the hoses (they get old and brittle and are really easy to break, as are the nipples they connect to), make sure you have all the clamps that hold the assemble together on tightly and securely, ie......tubing to MAF assemble, tubing to TB........

check your air box make sure it isn't cracked or there aren't any holes in it.....and basically just make sure you have the clamps on tight.....

about the check engine light:

since the check engine light is on and you are having problems with the idle, i would first check and or adjust/replace the throttle position sensor..... that in itself could trigger the check engine light as well as effect the idle

another culprit could be a bad MAF sensor, bad MAF would cause irregular idle (low, high, stumbling, ect.....) as well as trigger the check engine light.

[92Lex]

If there's a check engine light then can't you just hook up a scan tool to retrieve the code(s)?

[Jacob]

92Lex,

I’ve got the codes retrieved (two), and they indicated a catalytic converter efficiency problem. And I was quoted $2700 to have the catalytic converters and oxygen sensors replaced. I didn’t let them do the job because I didn’t have the money, besides the car passed the emission test which makes me skeptic about the cats’ efficiency.

I’ll try to solve the vacuum problem first, and see what happens to the check engine light.

Thank you all

Jacob

[92Lex]

Did you happen to know the exact code or did you let them tell you it had something to do with the cats?

[blake918]

He's probably looking at PO420 or 430. I remember a while back when you(Jacob) were discussing this, and I told you there was a procedure to check the O2 sensors. I finally found it in the book. I can post it up tomorrow since I don't have the books with me. I had a PO430 a little while ago. I was hoping that a piece of trash was on one of the O2 sensors, and sure enough after I blew the car out 75mph in 2nd gear, the light went out shortly thereafter. And hearing the V8 scream was a joy!! B)

Let's hope the MAF is not broken since that's a $800+ part. :o

92 and Lex, thanks for the help with my low idle. It's still 80deg weather over here and the A/C is always cranked down 99% of the time, but I suppose I will need to take care of it soon. It does get kind of aggrovating when I park because the p/s pump groans like hell because it's trying to work off of 500-rpms. I like your method of adjusting the tps!! It seems about 100x easier than Lexus's! Thanks!! :D

[Jacob]

That’s true, I was told it was PO420 and 430 (both banks). As for the oxygen sensors, I have already replaced them with Denso first time fit (about $119 for two sensors). Replacing the sensors didn’t solve the problem but it increased the mileage from 15 to 17-18 mpg (mostly city driving).

Jacob

[92Lex]

That’s true, I was told it was PO420 and 430 (both banks). As for the oxygen sensors, I have already replaced them with Denso first time fit (about $119 for two sensors). Replacing the sensors didn’t solve the problem but it increased the mileage from 15 to 17-18 mpg (mostly city driving).

Jacob

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I was gonna say there's no code for inefficient catalytic converter...the only way to know is if you're able to hook up a gas analyzer to it. So you replaced both O2S and you're still getting the same trouble code? What year is your car?

[Jacob]

1996 LS400 with 117K.

And, yes I'm still getting exactly the same codes.

Do you think a vacuum leak would cause such codes to be triggered?

Your help is highly appreciated

Jacob

[92Lex]

Did you change the O2 sensors before or after the catalytic converters? Yes, a vacuum leak can lead to those codes...maybe a vacuum valve assembly malfunction. The code is an indication that your cats just aren't working as well as they should at breaking down certain gasses. So let's say you have too much air somewhere before the O2 sensors...your catalytic converter wouldn't be as effective in breaking down the NOx..so it's not like your catalytic converters are bad so don't jump the gun and replace those. Like the others said, it may be your MAF sensor...but it can also be anything else from an EGR valve to excessive carbon build up in the combustion chamber causing higher combustion chamber temperature ----->> elevated NOx.

[Jacob]

I replaced the oxygen sensors before the catalytic converters. From what you wrote, I understand that diagnosing this problem is not easy, but I’ll keep trying :)

Thanks

Jacob

[92Lex]

I replaced the oxygen sensors before the catalytic converters. From what you wrote, I understand that diagnosing this problem is not easy, but I’ll keep trying  :)

Thanks

Jacob

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PO420 would be catalyst system efficiency below threshold (bank 1)...the thing that would be likely to send this code would be your downstream O2 sensors (after the catalytic converter). The O2 sensors you replaced before the cats wouldn't really be able to tell you that the catalyst system efficiency is below threshold, simply because it's measuring oxygen content before the catalytic converters. The O2 sensors before the cats would be measuring oxygen content entering the cats but not anything coming out of it, the O2 sensors after the catalytic converters are the one's that actually "see" what comes out. Have the O2 sensors after the catalytic converters checked out. Hope this helps.

[josh99blackls400]

I don't have any repair suggestionsl, but I can feel your pain...my '95 has a crazy low idle(in P and D4) when the a/c is off. It goes down under 500rpms, and hangs in the 400 range. The engine is perfectly 100% smooth even at that rediculous idle. However, when I turn the a/c on, the idle goes back to where it's supposed to be ~700rpms. The repair manual says the idle should be 650 +/-50. Here's a pic from a traffic jam the other day-I had the windows down because we actually had a nice day for once--a/c is off...

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<_<

my 99 ls400 idle @ 400 and sometimes lower when the a/c is on any recomandations