What is this sensor?
1988 2.5 liter 4 cylinder with 19k original miles.

I have replaced the temperature sensors over on the left side of the engine; on top of the cylinder head, and in the thermostat housing.

What is this sensor in the photos below?
Is it the intake Manifold Temperature Sensor?
It’s located on the right side, next to the “dog bone” mount.

Since this is a 1988 2.5 liter, things aren’t exactly the same as in the 84-87 model 4 cylinder engines.

It looks just like the same sensor that goes into the thermostat housing.

The reason I’m asking is because I finally got this Fiero all set and ready to drive it daily, and now it’s all of a sudden hesitating on acceleration; it’s popping.

Only does it under load

I had this running last night driving it all around and all WAS good.
Today, I drive it to the gas station to top off the gas tank; literally put 4.5 gallons of 91 octane premium in it.
Was jumping on the accelerator on my way there…. All WAS good.

I put the 4.5 gallons , pay for an automatic Ultra car wash, and as soon as I leave the gas station, it starts to “pop pop” and hesitates.

If I ease on the gas pedal, it does ok.

I have already replaced the following:
EGR Valve
Temp sensor in the T-stat housing
Temp gauge sensor in the cylinder head
New PCV valve
New air filter
New little breather element
New AC Delco plugs gap to .060
New plug wires
New valve cover gasket
ALL NEW coolant hoses… even heater hoses… all of them
New 180 degree thermostat
New heater core
All new antifreeze - burped out all air used Ogre’s fill procedure

All my vacuum lines are connected and nothing broken or cracked or visually worn on the vacuum lines.

I ran this Fiero all around last night
Totally fine
Today was totally fine all the way to gas station

Was thinking maybe got 4.5 gallons of bad gas from gas station???
Car wash got water In somewhere???

I checked the engine, nothing that stands out as obviously wet or anything.

The only thing I haven’t changed yet is the Fuel Filter.
But my Fiero ran perfect last night and today on my way to the gas station.

I’m stumped.

Was going to start throwing new parts on but would rather not.
I’m pricing the MAP sensor that’s on the air cleaner housing.
Throttle position sensor pricing too.
For AC Delco parts they are just under $50 each.

Then I see this sensor in the intake manifold (next to the “dog bone”)

SIGH and sadness
I don’t trust to drive to work tomorrow that’s 40 miles away … one way.

Any help and suggestions much appreciated.

quote Originally posted by enicho1: Since this is a 1988 2.5 liter, things aren’t exactly the same as in the 84-87 model 4 cylinder engines.

'88 duke is very similar to the '87. '84-'86 dukes are different.

quote Originally posted by enicho1: Today, I drive it to the gas station to top off the gas tank; literally put 4.5 gallons of 91 octane premium in it.

Why are you wasting your money on 91 octane Premium gas? The engine is designed to run best on 87 octane Regular.

quote Originally posted by enicho1: I put the 4.5 gallons , pay for an automatic Ultra car wash, and as soon as I leave the gas station, it starts to “pop pop” and hesitates.

I suspect that water was forced into electronics somewhere in the engine bay.


I went to The Ogres Cave (which for a lot of people is now next to impossible to access) and copied the following...

quote MAT sensor. 87+ 4 cylinders gain an additional sensor. The MAT (Manifold Air Temperature) sensor is located in the intake manifold to the right of the TBI unit. DO NOT over tighten the MAT sensor or you may split the intake manifold.

[This message has been edited by Patrick (edited 03-05-2023).]

Have you replaced the distributor cap and rotor?


I don't know if this chart is correct for the 1988 4cyl MAT so somebody might need to correct me on this. But this resistance chart applies to the temperature sensors that I've dealt with:

All 3 of the temp sensors should show similar resistance when the car is cold, unless the 4cyl MAT uses a different scale.


This shows the voltage coming off the signal wire for given amount of manifold air pressure:

I don't think MAP sensors fail very often.

There isn’t a cap and rotor on the 1988 2.5l

quote Originally posted by enicho1: There isn’t a cap and rotor on the 1988 2.5l

Whoops, forgot that.