I think the 34 has to do with the MAP sensor, but when I looked up the 23, it was a 'MAT' fault. What is this? I think it may be something to do with the throttle (????).

Can anyone help with either one??

Thanks

 

i think i responded to this over on fbody.com

 

Yeah, I posted both places.

Thanks

 

Unless you've converted your control scheme, your '89 should have a MAF sensor and not a MAP sensor.

The MAT (Manifold Air Temperature) is located on the underside of the plenum, and the error code you are reading is for an impossibly low intake air temperature reading from the MAT. That means that MAT resistance is beyond 100K ohms. That can be due to a failed or disconnected sensor, or open circuit.

 

Yea, isnt it like -30°F or something like that?

 

I haven't done anything to it.

I assume by plenum you are refering to a TPI car, so I can equate that to my air cleaner on my car, yes? I pulled the air cleaner off about a week ago and I can't remember if I hooked that wire back up to the sensor. So that may be the problem for that one. If not, then I guess it is the sensor. I am at work right now and it's not my daily driver, so I can't look at it.

But the MAP/ MAF thing has me confused, where on a TBI 305 is the MAF (mass air flow??) sensor located? I thought that MAF was only on MPFI/TPI cars. Excuse me if I seem a little ignorant about this, but I am not well read on sensors and such. I know what I think the MAP sensor is. It is a black rectangular piece located on the firewall above the passenger side head near the blower and a/c condenser housing. If this is the case, I know for a fact it is hooked up. So, could it be bad? There is only the one connector on it, right?

Thanks for all the help!

 

A 305 TBI engine does not have a MAF sensor. Those engines and the late-model TPI engines are speed density. Speed density systems use MAP sensors while MAF systems use MAF sensors, of course. You are correct about where your MAP sensors is. The sensor that is connected to the air cleaner is the IAT/MAT sensor. All it does is tell the engine the temperature of the air entering the engine.

 

Ok, good. It isn't as bad as it was seeming a little while ago. I thought I lost my MAF sensor too!! :LOL:

Does loosing the IAT/ MAT hurt the engine any or is it just and input parameter for the ECM? I will change it if it is bad (or connect it if it is unplugged).

I will test the MAP sensor tomorrow. Do you know what the resistance should be? If not, don't sweat it. I don't think my Chiltons tells me.

Thanks for all the help.

 

The MAT/IAT was disconnected from my car for a while (it wasn't my fault) and all that happened was the check engine light came on. I don't think it hurt the engine or made me lose power.

 

Opps! My mistake. I missed the part about the TBI.

Yes, you have a MAP, no plenum, and your MAT should be on the underside of the air cleaner or in the intake ductwork.

An open circuit MAT indicates a temperature below -40°. Disconnecting it will set that error code, as will a faulty sensor.



As for your "34", the MAP is sensig a lower absolute pressure (more vacuum) than is expected at a given throttle opening and engine RPM. You could also have a poor connection, low reference voltage, or poor grounding at the MAP sensor. Of course, the electrical connector needs to be clean and tightly seated.

The MAP sensor can be checked with a vacuum source and a digital voltmeter. The sensor should output a 0-5VDC signal at the 'B' terminal. The output voltage is based on absolute pressure at the hose connection. The sensor should output full voltage (5.0VDC) when there is one BAR (barometer, or atmosphere) of pressure applied. This means there is basically no vacuum (0" Hg) and the Absolute Pressure is at 14.7 PSIA.

When the Absolute Pressure decreases (due to vacuum) the voltage output on the 'B' terminal should decrease as well. Test the sensor down to about 20" Hg of vacuum, or 0.33 BAR (4.9 PSIA), where the output voltage should be around 0.8-1.2 VDC. The voltage should vary in direct proportion to the Absolute Pressure, or amount of vacuum applied. If the MAP output "jumps" or "sticks" at a given point, the sensor bridge circuit or the mechanical diaphragm is failing. Since there is no good way to repair a MAP sensor, replacement would be indicated.

 

Thanks for all the help you guys!

I looked this morning and the MAT was connected, but I did run it for about 15 minutes with the air cleaner off (and I disconnected the MAT). So I guess it stored that code. I will clear it and see if it comes back.

As far as the MAP, all the connections are tight. I will test it the best I can and replace if necessary.

Thanks again!! You all are always so helpful.

 

And it's a good thing that Benm109 is keeping an eye on me. I still would have been thinking "TPI" if not for that reply.

 

I cleared out the codes. I went ahead a bought a new MAP sensor. The MAP code is gone and the MAT code is gone. I have checked it and they haven't returned. But now the Code 32 is coming up again. So, I changed the solenoid with a spare I picked up from the junkyard a year or so ago (don't ask why, I just hoarked it from them). I just did it yesterday and haven't had a chance to get it on the open road. The EGR itself moves freely, so I will wait to change that.

Vader-- you have helped me with this before I think. I don't think I said that I disabled the AIR pump though. It is there and spins, but the guts are removed. It is essentially a pulley. I have read elsewhere that if the AIR pump isn't working properly, a code 32 is triggered. Is this so and could this be the problem? The light only comes on when I am on the highway at a good cruising speed which leads me to believe that it is egr related. I think the AIR system would come on regardless.

Thanks

 

The lack of air injection shouldn't affect the EGR operation nor error codes.

If you still have trouble with your EGR, try this routine:

 

Thanks!

 

The valve wouldn't hold vacuum. Replaced the valve. $51. I had to go to 4 different places to find it. My local Chevy dealer didn't even have one (for $88 I wouldn't have bought it from them anyway). No code.........yet.

Thanks for all the help!