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Brand new to me Jaguar XJ6 with a TPI. I've replaced vacuum hoses and replaced the IAC. Still idles very high at 1500. My scan tool says the ECM is hoping for 700rpm. I pulled the IAC to see if it was even moving. Oh it's moving....I put the ECM into diagnostic mode and everything I read says that should move the IAC fully out except mine does the exact opposite, it pulls in and shudders as though it would like to go in further. Is it possible the A high/low and B high/low wires are switched? I tested continuity on the wires from the ECM to the plug; all good. Tried the old IAC and it does the same crazy dance. Ignition on, diagnostic mode = dancing IAC. Ignition on, NO diagnostic mode and the IAC does absolutely nothing. Weird? Thanks in advance for any advice you can provide.
Re: Why is my IAC valve vibrating like this? (VIDEO)
Need to swap two like colored wires to the IAC. They are usually paired as two light greens then two light blues (with different color stripes). Swap either the two greens or the two blues, not both.
Note that if you do the diag test with the IAC in the open after the wires are swapped, the pintle will exit the IAC body. To re-install the pintle need to swap the wires back as they are now. Then swap them back once done.
Re: Why is my IAC valve vibrating like this? (VIDEO)
I took a picture of the current connections (nice black tape) and then traced each to the ECM (also tested for continuity, all good). Are you saying that I'll need to take both blue wires and switch them with the green wires? (
Last edited by pricebill; Apr 4, 2015 at 04:23 PM.
Re: Why is my IAC valve vibrating like this? (VIDEO)
Either swap the two greens with each other, or the two blues with each other. One pair or the other, not both, and not between blue & green. The IAC is a bi-polar stepper motor.
Re: Why is my IAC valve vibrating like this? (VIDEO)
Thanks RBob. Green wires switched and diagnostic mode now has the IAC heading out instead of in. I reversed the wires to get it to go back in and then resoldered the green wires switched. Sadly my idle now starts at 2000 and calms down to 1500. I put it into diagnostic mode and the idle screams at 2500. If I remove the IAC, extend the pintle manually to full out position and install without connecting it I get a nice 650-700rpm idle so I think I can effectively eliminate vacuum leaks as the cause.
Out of diagnostic mode and with the scanner plugged in the IAC doesn't move at all. Scanner says IAC position is 160 for start. Perhaps my ECM is broken? Shouldn't the IAC move a little at ignition or shut down?
Re: Why is my IAC valve vibrating like this? (VIDEO)
So from what I'm reading on this page http://www.gmtuners.com/tech/TPS_IAC.htm Generally, anything you see over 160 counts should be considered to be a near- or fully-open idle air passage.
So on fresh ignition, about to engage the starter, no diagnostic mode, I should be able to watch the IAC retract? Because mine doesn't (sigh). Neither does the old one.
OR do I need to take the advice from the above page and know that the ECM will only move the IAC into a correct position when...
The ECM “resets” the IAC valve when the car is operated at normal road speeds (35mph or more). During this time, the IAC valve is typically extended out all the way (IAC counts = 0), thus closing off the idle air passage. This helps the ECM “learn” the position of the IAC valve. Any time the IAC valve is replaced, this “learn” procedure should be performed.
Last edited by pricebill; Apr 6, 2015 at 07:12 PM.
Re: Why is my IAC valve vibrating like this? (VIDEO)
The IAC reset at a certain vehicle speed is done on some but not all vehicles/ECMs/Masks. Others reset the IAC at key-off.
Does your scan tool show the ECM stepping the IAC closed while idling? If not then the ECM doesn't think that the engine is in idle mode. This may be caused by a maladjusted TPS.
Re: Why is my IAC valve vibrating like this? (VIDEO)
Scan tool does show the IAC stepping from 160 back to 0 after a cold start (or even a hot one). TPS has been adjusted to .54v several times. My ECM appears to be a 1227730.
Re: Why is my IAC valve vibrating like this? (VIDEO)
With the $8D mask the TPS setting isn't critical (such as on MAF cars).
Definitely something strange going on. Can try this: Short A&B on the ALDL connector, do key-on, engine-off. After about 20 seconds unplug the IAC connector from the IAC and then key-off.
At this time the IAC should be fully closed. So remove the A&B jumper and start the engine. The idle speed should be low.
