I just got the X back from an engine swap, the IAT is missing and the hole is plugged.

It idles beautifully but anything over idle and it runs extremely badly unless it's at full throttle.

I will be getting a new IAT sensor but should the engine run that badly without it or should i be looking for something else as well?

 

If the IAT connector is open circuit, then this sensor missing could explain the truck running poorly. I wonder if the previous owner believed the sales pitch for the $0.02 resistor "performance chip" that folks sell on auction sites for $50 or more and decided to remove the IAT instead of just bypassing it.

I'm not sure which side of the MAF the IAT is on your truck, but if it's after the MAF and the hole is not completely plugged, that will contribute to the poor running as well.

-Rod

 

Definitely no resistor shenanigans, the truck was running great until someone who will remain nameless put 4 litres of trans fluid in the engine.

The hole was plugged, by a rubber tubeless valve stem - with the valve in it.

There were 2 complete engines, I don't know how I ended up with with no IAT sensor.

I saw the spare IAC sitting on the floor, but that wasn't it - there was one fitted.
The rubber hose going into the IAC doesn't look like a good fit though.

This is why I paid somebody else to do the engine swap.

 

Have you contacted the shop that installed the engine and explained the confusion (engine had the IAT before it was installed, engine runs poorly under load)?

-Rod

 

Yep, they know about it.
I worked out why I had no IAT sensor.

The donor vehicle was sitting around for a long time and I raided it for the sensor to see if that was what was wrong with a Mondeo (Contour) at the time. So that sensor is still around...somewhere.

The one that was supposed to go in with replacement engine was sold along with the inlet trunk while the LTD was in the shop.

I had totally forgotten/ didn't realise that I only had 1 sensor and that I didn't know where it was.

That's not the problem though, I'm buying another sensor tomorrow but I'm not convinced it's the whole of the reason why it's running so bad.

The shop has no idea so there's no point trying to get them to do anything.

I suppose what I can do is replace the sensor and clear the code and see if it throws any more codes.

 

Makes sense that it would run badly without that sensor. The computer measures how much air goes into the engine based on the MAF sensor, but it has to do a correction for air density by knowing the temperature of the air as it enters the engine. If it doesn't have a way of knowing, it does not do this correction, and the assumed values can be way different from the required values. If the computer does not know the density of the air, it will use an incorrect amount of fuel. Too rich or too lean, and viola, the engine runs poorly.

The shop sounds lousy. When doing an engine swap, you see whats different about the two engines, and surely there was a sensor on the old motor, so it should have been swapped to the new. You mean IAT, not IAC. If you run with no IAC, it is doubtful the motor would even idle.

 

I mean IAT sensor, definitely. The one in the intake trunk.

In the post before yours I explain that the shop didn't have the sensor.

It's my understanding that the IAT sensor just trims the fuel mixture for the best running in the climactic conditions and that the engine should run mostly ok, but not optimally, without it.

It idles dead smooth.

I'll find out tomorrow when the new sensor goes in.

 

So I replaced the IAT sensor and as I feared it wasn't the only thing wrong.
It runs better now but far from good.

I don't have to give it as much throttle to make it go now but coming off idle slowly it stumbles very badly and blows black smoke.

Does the switch on the throttle body activate something just off idle or is it there to activate something using more pedal movement?

I have an ELM 32 to read the codes but I haven't figured out how to use it. The PC doesn't seem to pick up the signal, I'll try the phone.

 

What switch off the throttle body are you referring to? There should be a Throttle Position Sensor (TPS) connected to the butterfly valve, but it's not just a switch, it's a potentiometer that provides a variable voltage back to the PCM to report throttle position.

You could have a simple vacuum leak somewhere, but the black exhaust would suggest a rich condition rather than a lean condition from a vacuum leak. You might want to pull a few spark plugs to see if they support a rich condition. Be sure to inspect the fuel system to make sure the fuel pressure regulator has a good vacuum source and that the line back to the tank is not kinked somewhere.

-Rod

 

I was looking at the way the TPS attaches to the throttle body, it looks like the throttle blade can move a fair bit before it engages the potentiometer.

If that's not right that could be my problem.

 

I'm not sure how you define "fair bit" but that doesn't seem right. Using a scan tool with datastream or the ELM327 route you should be able to see a very linear response from the TPS with any throttle input. You can also use a multimeter but that requires some creative mounting of the DMM or two people.

-Rod

 

Have a look at the 2 pics, by comparing the mounting holes you can see how the TPS screws on to the throttle body and how the throttle blade can move a fair way before the potentiometer is engaged.

 

Actually, in the pics it looks like there's no gap due to the angle of the potentiometers receivers.

 

I have an ELM327 but I'm having trouble getting readings.

 

I bought a used TPS to see if that made any difference.
I was hopeful because as you can see by the pics they are lined up differently.
But it made no difference.