89, 240, 173,000, Non-Turbo, Non-EGR


I am experiencing the following symptoms on a 240:

About a minute after the engine is started, the idle starts to drop, sometimes it stalls out, but sometimes it doesn't. The it starts to surge a bit as it starts to get warm. I found that if I keep the throttle open and the rpm at 1000 or more, it will stay running - I know that is a classic IACV problem - but after the engine is warm it becomes shaky and the idle is rough. There are no Trouble Codes being stored by either ECU. Both the IACV and the AMM passed the OHMS tests; but I do not put much credence in those ohms tests, since I have had bad IACV's with good ohms readings. The AMM also passed the voltage signal, heated wire, and burn off tests.

Are there symptoms that would be present with the AMM that might not be present with the IACV, or vice versa?

Parenthetically, the vehicle was running without problems. But it has been sitting still since Dec 1, 2006. I did not get it inspected and was not able to use it much during 2007. I did make short trips to a local convenience store in the evenings sometimes. At any rate, I am now disassembling and cleaning many of the engine parts, connectors, etc - the usual maintenance items. I discovered a leak in the accordion tubing where the one IACV hose connects to the tubing. And the Manifold brass tube that the small flame trap hose attaches to was clogged. However, correcting those problems does not the rough unstable idling after it is warmed up.

Btw, for those who would suggest a bad O2 sensor, the sensor is producing a 0.001 to 0.007, and sometimes a 0.008, at idle [but I did not road test it for voltage readings]. Adding some propane to the intake did cause the O2 sensor to respond with 0.008's. Perhaps a bit lazy but not the cause of this problem.

My experience with the IACV's is that if the valve part gets carboned up, but the electronic part is sound, the symptoms are rather mild like a small amount of fluctuating, and then cleaning moving valve seems to help. But I found that if the idling starts surging and hunting to the extreme, the IACV is beyond repair, and cleaning does nothing. I used to be afraid to let any solvent get into the back portion of the IACV, because I assumed there were actual small electronic transistors on a board in it. But I learned that they have just simple solenoid in them.

So what happens if the solvent [an alcohol based electronic cleaner] does get in there ?

Can't one just turn it over and let it drip back out and then dry it out an/or air blast it dry? I'm sayin that Solenoids are pretty beefy tough parts.

And, if the reason is that it causes a lubricant loss, then what about adding some electronic lubricant to the inside, or WD-40? (unless the lube was dry graphite?).

I have often wondered whether it was the cleaning or the lubing of the IACV's that makes the difference in how it performs after either procedure, or if it was just a matter of the ECU resetting itself that was the fix? If I knew that answer I wouldn't be asking.


thanks diyer