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MAT sensor?...low idle problems?

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You know, that's funny. I was actually going to PM you and asked you if you ever got this fixed. Mine idles really low too and I've replaced every sensor with a brand new part. Did you try blowing out all the ccv lines yet to make sure no air flow was restricted? Mine are all brand new but I still get a bit of oil in my oil filter because I never pulled the VC off and cleaned up the inside. When you pull the line that comes off the back of the VC at the intake mani does the idle go up?

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Maybe you mean MAP sensor ? Manifold Absolute Pressure.


It is located on the firewall, center of engine. Wires on one side and vac hose to TB on other. Its basically a elevation control for the computer.






nope, MAT sensor located on the intake manifold. i'm told that I have one...it measures incoming air temp and a faulty one can affect air/fuel mixture, which could explain the issues.


as for idle screw...nope. i've swapped the throttle body 3 times with three different ones and that doesn't fix the low idle issue. most, if not all vacuum leaks are fixed, MAP is replaced, CPS replaced, ICM replaced, dizzy replaced and new plugs and wires.


as for the PCV system...well, i removed it entirely. it wasn't plugged, but the ends on the valve cover were plugged. it now has a small filter where the large hose went, and the small hose still goes to the manifold.


and no, i don't have to pass smog or emissions here :brows:


oh! i've been pulling as high as 17.74mpg out of it....so it can't be running THAT bad though it is a few mpg short for highway mileage...

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Well then how bout your TPS. Is it new and did you try adjusting it?


not new, but the sensors on the throttle body (TPS and IAC) have been swapped various times...that's what I accomplished by swapping throttle bodies (off perfect running vehicles mind you)

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Be careful if you swap the MAT sensor......I snapped my old one off flush with the manifold when I changed mine. What should have been a 10 minute job turned into a 2 hour nightmare (getting the remnants of the old sensor out). The factory used copious amounts of threadlocker on it when they put it in.



I wasn't having any performance issues, I just swapped it as a refresh of all the stock sensors. Didn't notice any difference with the new one, so I would assume my old one was still working.....



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Could also be affected by the CTS. MAT and CTS work in parallel.


The coolant temperature sensor is installed in the engine

water jacket on the left side of the engine. It provides

input voltage to the ECU. As coolant temperatures vary, the Coolant

Temperature Sensor resistance changes, resulting in a different input

voltage to the ECU. The ECU calculates this information and adjusts

the following:

* Adjust fuel injector pulse width. Colder coolanttemperatures will result in longer injector pulse width

and richer air-fuel mixtures.

* Compensate for fuel condensation in the intake manifold.

* Control engine warm-up idle speed.

* Increase ignition advance when the coolant is cold.

* Energize the EGR valve solenoid, thus preventing the flow of vaccum to the EGR valve.



The Manifold Air Temperature (MAT) sensor is installed in the

intake manifold with the sensor element extending into the air-fuel stream. The MAT sensor provides an input voltage to the

ECU. As the temperature of the air-fuel stream in the manifold varies,

resistance changes, resulting in a different input voltage to the ECU.




Manifold Air Temperature (MAT) Sensor

1) Disconnect the electrical connector from the sensor. Using

a high impedance, digital volt/ohmmeter, measure the resistance of the

sensor. If measured resistance is not as specified, replace sensor.


2) Test electrical harness resistance of both sensors by

testing between ECU harness connector "D-3" and sensor connector. Also

test between sensor connector and ECU harness connector "C-10" ("C-8"

on MAT sensor). Repair wire if open circuit is detected. Repair MAT

sensor wiring harness if resistance is greater than one ohm.



F © Ohms

212 (100) .................................. 185

160 (71) ................................... 450

100 (38) .................................. 1600

70 (21) ................................... 3400

40 (4) .................................... 7500

20 (-7) ................................. 13,500

0 (-18) ................................. 25,000

-40 (-40) .............................. 100,700


Just in case ya wanna know:


The MAP sensor reacts to absolute pressure in the intake

manifold and provides an input signal to the ECU. As the engine load

changes, manifold pressure varies, which causes the MAP sensor

resistance to change, resulting in a different input voltage to the

ECU. The input voltage level supplies the ECU with information

relating to ambient barometric pressure during engine start-up or

regarding engine load while the engine is running. The ECU calculates

this information and adjusts the air-fuel mixture accordingly.

The MAP sensor is mounted under the hood on the firewall and

is connected to the throttle body with a vacuum hose.

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thanks a ton!


I'll be looking into that.


is the temp sensor you're discussing the small single pin one on the upper rear driver's side of the block? or is there another one?


I believe the one you are mentioning is the guage sensor. I have seen the Coolant Temperature Sensor in 2 locations; the location on the left side of the block is direectly under the intake/exhaust manifold, the other location is in the Thermostat housing. If you have a standard Thermostat housing then it's in the water jacket on the left side under the intake. This one is often affected by exhaust heat embrittlement, the wire insulation melts allowing it to short or build up corrosion throwing the resistance out of whack.

A simple Test.

This time of the year on a cold engine you should read 7,000 ohms with the CTS unplugged. Plug it back in and start the engine and bring it up to normal operating temperature. Unplug it again and it should read 1,000 ohms with the engine warm. A little variation is OK but not more than 5% or the ECU reading will be out of adjustment. Replace the CTS if the resistance is not in the above range.

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... I still get a bit of oil in my oil filter...


Gosh I hope so Chico! :D





I see my mistake :oops: I meant oil in my air filter.

I'm :popcorn: because I had my CTS changed and it didn't make a differnce in my idle. Although the moron who did it wrapped that white tape around the threads. (I just noticed it when I had my front end off).

Maybe that's messing up the signal. I'll have to check the resistance now.

Thanks for the info brig.

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