IACV transfer and beats

Supercharged Previas like mine have an extra 25 hp out of the factory compared to the naturally aspirated variants (135 vs 160), but along with that power boost came a bunch of extra complexity beyond the nearly inaccessible supercharger itself. There’s a different radiator with extra holes, and those extra holes go to extra plumbing elsewhere. All this extra plumbing means more hoses to breakdown over 20 years, which means the coolant in these vans often ends up, as Chris Plummer pointed out, “looking like assbarf.” I decided to put a Mr. Gasket clearview fuel filter in the coolant line leading to the IACV to see if TRO had the same problem. Photo Mar 28, 17 56 44

Indeed it did.

A side effect of the filthy coolant is a tendency for these vans to end up with a high idle. Basically, the IACV (idle air control valve) judges whether the engine is cold by the coolant temperature, and if it’s cold, it raises the idle until the optimal operating temperature is reached. A narrow opening leading to the sensor can get gunked up pretty easily with the black flakes of hose that made their way there in the filthy coolant, and as a result, the IACV never actually senses the temperature of the coolant and never thinks the engine is up to operating temperature, resulting in a wacky high idle. Photo Mar 28, 16 18 28

I had already cleaned out black flakes (which were really more hamburger colored in this case)  and rebuilt the IACV on TGO and didn’t actually get around to posting about it, but it gets a second chance since it’s going in TRO. While TRO already had some black flakes in the crucial T-junction, TGO hadn’t so I knew the dysfunction must have lived deeper down. I ordered a new gasket for it and got some carb cleaner, which you know is the good stuff since it’s banned in California, and got to work. While I can’t explain the chemical reaction that made this goop happen, it had definitely happened long enough ago that it wasn’t easy to get it out.

Photo Apr 13, 19 03 57 Photo Apr 13, 19 04 10

After some elbow grease and probably a lot of inhaled carb cleaner, I got the valve clean, and put it back together, which seemed to help, if not resolve the idle issues.

Photo Apr 15, 10 21 52 Photo Apr 15, 10 21 37

Elsewhere in the van, a new issue developed, namely that the front right brake was refusing to release its grip on the rotor. While there was a burning smell at times, I just figured it was the valve cover gasket, which is not an uncommon issue on Previas. On a particularly humid day, it became clear in an acrid cloud of smoke that the burning smell was coming from that sticking caliper. Because this issue opened something of a Pandora’s box, and as of yet is technically unresolved, I will devote an entire post to that later on. In this idle time between brakes that were always on and brakes that were never on, I decided to turn some attention to the inside of the van. When I bought TRO, it came with a bunch of extra parts, as well as an aftermarket head unit, a Jenson with a touchscreen that, while not technically period correct to the van, is from an era when an in-dash touchscreen was a novel idea (remember that?). Photo Apr 26, 9 26 36

This head unit also has a number of input options for both audio and video, which made me think that not only should I install the head unit, I should connect a Sega Genesis to it in order to properly and period correctly pimp my ride.

Photo Apr 29, 18 41 17

The dashboard dis-assembly itself was straightforward, especially with detailed instructions from Crutchfield, which they helpfully sent along with the wiring harness for it… Then I found out about the “Premium sound option” that my van was equipped with. In 1995, this meant a CD player (Premium), an external amp (Premium!), and a subwoofer in the back (!!). This also means that when the original head unit is pulled out, the connector looks nothing like the one that comes on most Toyotas, or the wiring harness that I had ordered, and in fact is the one used in Lexuses (like I said, Premium!). It took a long time to figure this out, since there are extra connectors back there too, that seemed to be connected to nothing (?).

Photo Apr 29, 20 04 23

I found a a Lexus wiring harness at a small audio shop in Hadley, and respliced everything, now including the pre-amp outs on the headunit. While everything connected together at this point, there was still a problem. The premium audio connection behind the head unit connects to a Fujitsu Ten (Eclipse) amp under the glovebox, which is slick, but proprietary, and gain can’t be adjusted, resulting an an awful hiss. More research revealed that the proper way to connect aftermarket headunits to Toyota Premium Audio equipped vans is to bypass the whole thing and connect to the speakers after the amp. When I took apart the glovebox and got under the right side of the dash, I found the amp and unbolted it from its bracket and it was indeed the standard Toyota connector on the back of the amp. Sorry I doubted you, Crutchfield.


I pulled the head unit out of the dash and put it on the passenger side footwell to see what happened when I connected directly. It plugged right in and worked great, with no hiss, which solved one problem, but introduced another. I couldn’t leave the head unit just hanging out on the passenger side floor, but it had to connect to something about 2 feet away with about 6 inches of wire. While I could have just spliced in a whole bunch of wire, I was concerned about the number of wires and the likelihood of getting at least one of the connections wrong, so I decided to try something different.

Photo May 14, 11 27 05

Since the connection I was working with at this point was the standard fit on most Toyotas, I went to the junkyard down the street, and ripped wiring harnesses out of a couple of crashed Corollas. I mapped the wire colors (they’re different behind the dash) and connected the male end of one harness with the female end of another to effectively make an audio extension cord. I snaked it in behind the dash, connected one end to the speakers and the other to the head unit, taking the opportunity to put in some TGO interior parts that were in better shape, crossed my fingers, and powered on.


Sort of. While the stereo was now working with no hiss, it was not responding well to video input. But all was not lost, thanks to my factory service manual. More on that next post, as well as adventures in polymers.

In a van unrelated note, devoted PD reader and owner of the most famous balls in NECX Ryan Kelly’s family is going through some tough times and I encourage you to contribute to the GoFundMe that was set up to help them with medical bills, if you haven’t already.


About previadiaries

Ride bike. Drive Van.
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