Tried the IAC clean, and it didn't get rid of the p0505 code. Then did a complete tune-up (spark plugs, wires, rotor, cap) and oil change (filter &airfilter), still got the code. Then, I finally bit the bullet and installed a new IAC. Still getting the code. The only thing that has changed is that the light only comes on sometimes now. I can't figure out what is causing it, because it happens when it is cold or warm. When it does come on, I notice a marked sluggishness in the engine and rough idling. Does anyone have suggestions?

Take Care, Sharon[/align]

 

You might have a vacuum leak somewhere, including a possible intake gasket leak.

 

Forgot to mention, it occassionally backfires (once) on startup. And it isn't the only code I get. I get a p0505 and a _ _ _ _ _ and then a 'Done'.

Thanks and take care, Sharon

 

That kind of backs up my vacuum leak theory. Vacuum leaks cause lean conditions, which in turn cause backfiring. Incorrect ignition or valve timing can also cause backfiring, but tend to be more consistent in causing a problem. The vacuum leak problem can be intermittent if the leak is on the secondary side of any type of vacuum controlling switch. As the switch turns on or off, the problem can come and go because of the change in vacuum demand.

 

Sharon,

If you do a smoke check on the vaccum lines, you'll save a bunch of time hunting for the bad tube/hose.

If finding NO vaccum leaks, a simple and quick fix to prevent the engine from running very lean at idle is to adjust thebutterfly valvescrew on the TB. This screw sets how much the butterfly valves on the TB stay open or shut. Adjusting it slight will bring the rpm's up just a little. If the screw is frozen tight to the TB, some metal shim stock could help.

To test out this method, get some aluminum foil tape. Put it over the screw tip that the throttle bracket hits that is spring loaded to the butterfly valve. See the image below. The bracket has that spring wound on the right side in the picture. Just pull that bracket back and you'll see the bottom end of the screw.

 

There are very few vacuum hoses on this B1500 van, from what I can see. I checked them all and there is no break or crack or disconnect. I did find two valve seal bolts that were loose, with oil coming out of them. That is new since my recent oil change (where they overfilled). I tightened them down and all is fine now.I don't see any other air leaks.

I changed the crankcase breather and pcv, just in case. This made the backfire situation go away, for some reason.

Yesterday I drove it stopping and startingfor about 10 minutes - light on.Then I drove it for a half hour with the same stopping and restarting - no light. Then the light came back on. This is driving me bonkers.

I hate to mess with the manual adjustment, because it is not running rough at idle. It only seems to have no get up and go on acceleration, although that seemed to improve after the pcv and breather.Once it is up to speed, it goes down the road fine, at high speeds. Gas mileage is down to 10-12 mpg. Pretty bad. So, something is definitely wrong.

Alloro, you mentioned vacuum controllingswitches when you were discussing vacuum leaks.Could it be a male-functioning switch? If so, can you tell me which switches control vacuum?

Keep in mind, when you are thinking about this, that the vehicle had 50,000 miles on it before the spark plugs were changed (don't chastise me, it was the previous owner); so most likely, anything that would have been changed during a routine maintenance was most likely never changed. If I am missing something that should have been done, please let me know.

Things done:
oil change with filter & lube
new spark plugs
new wires
distributer cap
rotor
air filter
pcv
crankcase breather

Thanks for your help and take care, Sharon

 

Classic bad O2 sensor symptom.
A bad O2 sensor would also effect the air/fuel mixture.

 

Whoa, that is an expensive little part. Is there any way of testing to make sure that this is bad before I go out and spend more needless money?

Thanks and Take Care, Sharon

 

Check out the bottom of this page for both in vehicle and out of vehicle O2 sensor testing.
http://www.mr2.com/TEXT/O2_Sensor.html

 

Don't have the equipment to do that. And I thought that other codes would be set if the O2 sensor was not functioning properly. I have no other codes than the P0505

Thanks and take care, Sharon