Anyone ever throw a MAT sensor code? I'm not sure what the sensor looks like. I don't find it in my Chilton's manual either. Is it what reads the coolant temp. on the lower portion of the TB? When I read the code it says it may or may not be the sensor. What should I check before replacing it? Thanks, BTW what other sub forum should I post this? The car seems to run fine, but after it comes up to normal operating temps it throws the code. If I get on the freeway before it warms up, it wont come on until I get into town and am @ idle for a while at a red light. I didn't throw this until after the TB/runner swap. I'm wondering if the IAC in the older coolant cover assembly is bad as it was from another TPI set up I had for my '54. Any help is appreciated. Thanks, Daniel U

Daniel,
The MAT sensor is located on the bottom/rear of the plenum. Manifold air temperature. Are you getting code 23 or 25? Maybe it's not plugged in. You damn near have to remove the plenum to get to it. The MAT sensor measures air temperature, the ECM adjusts the fuel volume depending on the incoming air temperature.
I've never had a MAT related code thrown on any of my TPI cars. I do monitor the MAT reading sometimes to see the difference my IROC cowl hood makes in air temperature compared to my other 2 TPI cars. It's usually about 20 degrees cooler because of the hood scoop.

Thanks, I think I know what I did. I have 1 tube with a 90deg boot on it that I had no idea where it went. Maybe I'll try to find it without removing the plenum. "Code 23" Thanks, Daniel U Maybe my cowl hood has helped the delay in the code when I'm on the freeway?

Thanks, I got it plugged back in. I took off the small plastic dist. cover and saw the plug and sensor I had previously overlooked. I appreciate the help man! I still have 1 vacuum line with a 90 deg boot I need to find a home for, but it doesn't seem to be affecting the ECM or drivability.

On a side note, I was off work today. I had time to remove the rear seats(as they are never used), rear seat belts, and clean/vacuum the entire interior. I'll keep them in the rafters for safe keeping as they are in great shape. I'd like to find some nice lightwieght seats(15lbs or less)that are still comfortable and ready for 5 pt. harness. Then yank the current seats/belts, install new headliner and dash with a nice cage. ..........Did I mention I still need to finish my truck?

That sounds like the one for the interior vacuum controls. The one that works the duct when you switch the temp control from cold to hot and vice versa. It should plug onto the vacuum line on the rear passenger side of the plenum by the fuel pressure vacuum line.

There are 2 lines that go from the rear pass. side towards the front. Where do they plug into from there? I'll try to get some pics up later today. Thanks, Daniel U

Daniel,
The 2 vacume sources on the plenum that Kevin mentioned feed the fuel regulator and the other one feeds what Kevin said. The fuel regulator vacume line on my car has a 90 degree boot.
The 2 vacume lines from the EGR controller which is what your asking about goes under the plenum and 1 hooks up to the EGR valve and the other goes foreward to a vacume source on the bottom of the throttle body which has a tee connector.

Here's the ones I'm talking about:
This is wher they come from



An here's the end with the 90 deg. boot

Sorry, she's filthy under the hood. She's my DD and leaks/burns oil.

that last one go's to the bottom of the throttle body, right about where it is in that pic. Its one of the ones your pointing at in the other pic, the other go's to the egr valve under the plenum.

There's a niple on the stock TB, but nothing on the Summit 58mm one. What do you guys suggest I do? Plug it? What did that line go on the TB for?

You're supposed to transfer the nipple from the stock TB to the aftermarket TB. That line gives vacuum to the EGR solenoid to make the EGR valve work.

????The nipple is cast into the stock TB. How would I do that?

So this new TB is obviously not a CARB or CA. Smog legal part, right?

Are you sure its cast in? On mine it will pull out with a little force from a pair of vise grips.

The vise grips didn't work. The nipple looks cast to me. I might fab up my own. I just need to remember if there was a hole there on the new one or if I'll have to port one myself. Will this fail on the emmissions? Will there be a code? It doesn't seem to bother my ECM. Just curious.

Yes, the EGR valve gets its vacuum to open and close from that port. The SES light shouldnt turn on during the test at that MPH, but it will cause the emissions numbers to be higher. If the tech sees the line not connected, he could fail you, too.

Thanks for the info.