P0446; rough idle

[nicole_fl]

Hi All,

I have a 97 Camry with 2.2l 4 cyl; auto trans, 145K. Engine light on.
Problem is idle- smooth at 650 rpm, but when in gear, it periodically dips down to a near stall for just a moment, then returns to a smooth 650. In P or N it does this much less often, though sometimes I get a dip here too. The motor pulls smooth on acceleration. Does the idle dip hot or cold.

Diagnostic code P0446. This is for the fuel vapor recovery. Inspected cap, looks fine, made sureit was tight. Inspected hoses going into charcoal cannister, they seem supple and still attached.

To get started, would a problem in the P0446 system cause my observed idle problem? (If it can not account for the problem, I can find other ways to get my hands dirty and break nails.)

PS: I did find a small crack in the molded plastic part that runs between the airfilter housing and the intake manifold. I patched that up with high temp silicon sealant, but this did not solve the problem.

Car has a new timing belt, airfilter.
Thanks folks

[Mike Gerber]

Try cleaning the throttle body and the idle air control valve. They are the most common causes of the idle dip you are describing. Pay particular attention to spraying the cleaner liberally down in to the square or diamond shaped port in the base of the throttle body. That port leads to the idle air control valve, where the problem probably exists. Spray down in to the port first, and then go on to clean the rest of the throttle body while the cleaner soaks. Here is a thread with some great pictures on how to do it:

How to: Cleaning Throttle Body -4 Cylinder Engines- With Pictures

I don't believe this is related to your P0446 code. That is usually a separate issue with the evap control system. You might just want to try resetting the code and see if it returns. If it returns, in addition to what you have already checked, do a search for "VSV" or "Vacuum Switching Valve". They can go out as these cars rack up a lot of mileage and cause that code. It's usually accompanied by a P0440 code.

Mike

[nicole_fl]

Mike, fantastic. I will give it a try this weekend. Looking forward to doing this. Thanks for your tips, I will post after cleaning the throttle body. If that does not work I will try and track down this VSV you mentioned.
Nicole

[nicole_fl]

Well, after thoroughly cleaning the throttle body and IAC off the car, I still have the trouble with idle. The IAC solenoid resistances were in spec, and when voltage was applied to the solenoid the valve opened and closed as required. I bvelieve there is nothing obviously wrong with the IAC. So one question would be if voltages are being applied to the IAC to close it, at the wrong time. I am going to get a friend to check the harness that runs to the IAC and see if close voltages are being output at the wrong time (in other words, when the car is idling in gear.

Also, I inspected and replaced a few vacuum lines.(but they really did not look bad, just superstition.

I also just put in a can of seafoam into the gas tank to see if that helps at all.

Again, I note that only when in gear, does the idle randomly drop from spec to 450 rpm, and then recover. This "blip" is short, a fraction of a second long. When in park or neutral, it is extremely rare to see the idle drop. It appears to have gotten worse over the last month, so I am wondering if soon I will be facing stalling.

Anybody out there have a sense of anything else that should be checked? I am wondering if this could be a problem with the computer, sending the wrong voltages to the IAC?

Thanks million,
Nicole

[nicole_fl]

Problem solved! After finding this link:
http://www.fixya.com/cars/t1288853-i...e_in_gear_stop

I removed and cleaned the contacts on the spark plug wires. Idle as smooth as to be expected for a car with 155K mileage.

So, here is the real question:

Why didn't a bad contact on the spark wires cause this problem at idle in park or neutral??

If the argument is made that this needs to be under load to show up, why didn't this happen when I was driving or accelerating?

Having fun,

Nicole