Intermittent Idle Problem

[ChrisLS40094]

I have a 1994 LS400, w/ roughly about 130,000 miles. It seems about 60-70% of the time the car seems to run fine without a hitch. Then there are times, especially on rainy and humid days, that the car just doesnt seem to act normal. For example, when idling, the tach needle fluctuates from about 600 RPM's to around 1500 RPM's. This sometimes happens up to about five minutes. While this fluctuation occurs, black smoke is visible from the exhaust.

So the next thing I do is check for any error codes, and to my surprise no error codes are stored, hmmm, go figure. (This was two weeks ago)

Then today, while driving home for lunch, I noticed the check engine light came on for only a few seconds. Good. Now I can detect an error code and find out what the problem is... To my surprise I am getting error code 22 (engine coolant signal/sensor). This is not a code I was expect considering the car is not low on coolant and doesn't seem to be running hot.

I was initially thinking maybe the MAF sensor was the problem, since that seems to be a popular problem on this forum with similar symptoms to mine, but now I am at lost. Anyone who has any advice where to go from here or has had this problem before would be much appreciated. :)

[93ls400walt]

Welcome!

If this is happinging on " damp " days. I would look for a shorting out wire. In the dark you may be able to see arching. Or at least hear it. When the car is acting up.

Lexus and other places sell BG44K. A fuel and intake cleaner. Look for part # 208 for the in tank cleaner. Around twenty dollars. Also BG has a spray throttle body/plate and Idle air control valve cleaner. The kit from Lexus today was $40.00 for both. These may help with your overall preformance amd idle.

Look at Bg's web site www.bgprod.com for more info.

Idle probs seam to be a common prob. Please let us know your results

Walt

[SKperformance]

Is it the tach flucuating or the engine rpm's flucutating.

Difference is one is the engine and one is the dash.

It helps if you reread your posts .

[ChrisLS40094]

It is definately the engine and not the dash. The engine starts normally, then after a few seconds it begins to race, seconds later it will rev down to about 600 RPM's, another few seconds later, back up to 1500 RPM's. This seems to happen more often with the AC on and on rainy days, although it has happened on dry sunny days too, just not as often.

[SKperformance]

clean your throttle body

[Ross W.]

It is definately the engine and not the dash. The engine starts normally, then after a few seconds it begins to race, seconds later it will rev down to about 600 RPM's, another few seconds later, back up to 1500 RPM's. This seems to happen more often with the AC on and on rainy days, although it has happened on dry sunny days too, just not as often.

If you've got a code 22, check the sensor itself and the wiring leading to it, as well as the connector. The computer is putting the engine into "stagger back to the dealer mode"; basically it runs the engine full rich to make sure the engine does not stall, as well as keep the engine a little cooler if there's a catastrophic failure of the cooling system. Also consider the throttle position switch. These cars are known for those failing. Mine did and it had an up-and-down idle after it failed, much as you've described. Definitely clean the intake system after you've resolved the situation, and check the spark plugs to make sure they're not fouled.

[ChrisLS40094]

clean your throttle body

The throttle body was thoroughly cleaned about 1,000 miles ago.

I checked the error codes again last night after seeing the check engine light come on again. This time I got codes 14 and 22.

[ChrisLS40094]

I just noticed today that there seems to be a hissing sound around the intake and some of the vacuum hoses. Could a vacuum leak possibly cause the symptoms i described earlier?

[Threadcutter]

I just noticed today that there seems to be a hissing sound around the intake and some of the vacuum hoses. Could a vacuum leak possibly cause the symptoms i described earlier?

Chris:

Temporarily remove the vacuum hose going into the front of your air chamber/intake manifold.............That'll answer yer question "right quick"!..............

I'm referring to the black hose in the upper right hand corner of the picture. Pull it straight off of the nipple it's a ttached to & see how long the car runs for..............

[scotty2hottyoki]

I just noticed today that there seems to be a hissing sound around the intake and some of the vacuum hoses. Could a vacuum leak possibly cause the symptoms i described earlier?

Chris:

Temporarily remove the vacuum hose going into the front of your air chamber/intake manifold.............That'll answer yer question "right quick"!..............

I'm referring to the black hose in the upper right hand corner of the picture. Pull it straight off of the nipple it's a ttached to & see how long the car runs for..............

The skinny hose from coming from the lexus sign, and the other skinny hose that is coming from the air intake which come together (in the upper right)...it has a hard plastic nipple connecting the two at the end...where does that "nipple" connect to? because mine is loose and my mechanic said it was part of the power steering...is that true? could those hoses mess up the drive performance of my car?