Idle Only Issue

[Sully]

A while back, Jonheld wrote the following in response to Gordopescado's idling issue:
"Please answer my question. Is this an IDLE ONLY issue? Does the truck run fine off idle? Can you accelerate normally?
If the answer to the above questions is YES, then it points conclusively to unmetered air entering the system; assuming the parts replaced in the first post were installed correctly, calibrated properly, and are OEM. Off idle the intake vacuum is greater and the system is less effected by the leak (economy will suffer).
Air can enter from: crack/leak in the intake plenum (most common), oil filler cap (gasket can pop out), PCV (gasket/hose gets old and brittle), oil dipstick (gasket), side cover gasket (oil leak when running), valve cover gasket (oil leak when running), and a dozen other places.
Faulty EGR system is usually associated with the "turbo boost" feeling around 2200 RPM while accelerating, but given the age of your truck the majority of rubber parts will need replacing."

The issues described by Gordopescado sound exactly like my truck. While idling, and only while idling, the RPMs are dropping down into the 400s and sometimes lower. Occasionally, it will stall out- usually while I'm in a crowded parking lot. It runs fine when I give it gas.

My questions here are these-
1. How does one track down where unmetered air is or would be entering?
2. Would cold weather and/or a cold engine have any effect on this? (My problem is more pronounced when the engine/weather are cold.)
3. Could someone please explain to the slow kid why this problem would affect fuel economy?

Thanks.
-the slow kid

 

[trscott]

I recently had a similar problem right after an oil and lube on a very cold day. I stopped in at Texaco quick change shop. The truck was running perfect when I pulled in and wouldn't idle reliably when I left. I looked and looked and could not see anything wrong until someone mentioned the pleats in the intake tube that connects to the fuel injection intake. I still couldn't see anything wrong with it until I opened up my air cleaner and lifted the air box lid. Then I could easily see that the bottom half of the pleated hose was cracked almost 2/3 of the way through. When the air box lid was closed, the crack closed up enough that I couldn't see anything from above, with the crack being in the root of one of the pleats. Taking the old one off, I found that it had become very brittle with age, and new one was very flexible.

Of course the new one is clearly made of some rare and exotic elastomer which must require cross-breeding silk worms with rubber plants or something exotic like that - it cost $90 at the Toyota parts counter!!!

 

[80t0ylc]

Is this an ongoing problem? Reason I ask is that I notice you have a '94 as do I. '93 & '94 ECUs are particularly sensitive to having the 12 volts removed. Like, when you disco the battery. They actually have to "re-learn" to give proper idle speed and can take as many as 10 starts of the engine to get idle speed back to normal. You might have another problem if it continually does not idle, but if you have disco'd the battery recently, it should correct itself. And then the next time the ECU is "starved" of 12 volts, you start the process all over again!

 

[jonheld]

Of course the new one is clearly made of some rare and exotic elastomer which must require cross-breeding silk worms with rubber plants or something exotic like that - it cost $90 at the Toyota parts counter!!!

It costs $90 and lasts 16 years. Do the math. You get what you pay for.

 

[jonheld]

My questions here are these-
1. How does one track down where unmetered air is or would be entering?
2. Would cold weather and/or a cold engine have any effect on this? (My problem is more pronounced when the engine/weather are cold.)
3. Could someone please explain to the slow kid why this problem would affect fuel economy?

1. I would start with my eyeballs. Look at the parts mentioned.
2. Not sure. Typically on a cold engine startup the idle is up around 1000 or so, the ECU isn't looking at the O2 sensors yet, and I believe it's in a closed loop until water temp starts to come up.
However, if you have a gaping hole in your intake I'm not certain what it will do. It still has to base fuel delivery on the AFM, TPS, and RPM of the motor.
3. You're allowing unmetered air into the system. The ECU doesn't see it. It bases its fuel and spark delivery on sensor input. Now you have a situation where one sensor (the AFM) is essentially giving faulty info.