1996 explorer 4.0 ohv: is the IAT sensor threaded or push on?

[lobo411]

Hello! Haven't posted here in years since my x has been running like a top. I developed codes 171 and 174 (lean) recently after replacing the plugs. I found that I had broken one of the hard vac lines while replacing the plugs so I fixed that, but I still have the codes. My next target is the egr valve gasket, since I removed that to do the plugs on the driver's side and it's only a $3 item.

Meanwhile, I ran the scanner and noticed that my intake air temp sensor is reading 100 F (after a drive, so heat soak might affect the temp but I don't think this much) when it's only 50 outside. I have a cold air intake too, so I was thinking this might have something to do with it. The truck has 200k and the sensor is original, so I don't mind replacing it. I'd like to do it tomorrow or the next day, but I can't order the part without knowing if it screws into the plastic air tube, or if it's the push on type. And I'm at work so I can't check until tomorrow. I'd like to get it ordered, so... Anyone know? Thanks!

 

[lobo411]

Well, I checked the live data on first start this morning and the IAT is reading correctly. It was reading high before because it was sucking air from the engine compartment.

Anyway, I tried cleaning the MAF and that didn't help. However, on two previous occasions since the lean codes started, the engine stalled at stopped/idle. This engine has never stalled in 200,000 miles/26 years, so that made me suspect it was more than a simple vac leak or a minor upper intake manifold gasket issue.

You have to disconnect the EGR and move the EGR pipe in order to do the plugs on the 4.0, so I suspected that the EGR was involved in the stalling/lean condition. Today I decided to clean the EGR valve, and when I was taking it apart, I *think* I found the cause. I removed both EGR mounting bolts partway, and I noticed that the EGR valve gasket was not attached on one side. The bolts go thru the gasket, so unless I somehow confused myself (by removing and then reinserting the bolt), that means that the EGR gasket was only partially in place...which would make it impossible to get it to seal. So I cleaned everything and reassembled with a new gasket.

Now, these kinds of codes are notorious for "I fixed it! Oh wait...no...it's back..." So I'm not declaring victory yet, but I did notice that the short term idle fuel trim looked very good on first startup. Previously, it had been horrendous: +25 to +35%. Now it's more like -5% to 5%. So there's hope!

 

[Pete Deering]

Well, I checked the live data on first start this morning and the IAT is reading correctly. It was reading high before because it was sucking air from the engine compartment.

Anyway, I tried cleaning the MAF and that didn't help. However, on two previous occasions since the lean codes started, the engine stalled at stopped/idle. This engine has never stalled in 200,000 miles/26 years, so that made me suspect it was more than a simple vac leak or a minor upper intake manifold gasket issue.

You have to disconnect the EGR and move the EGR pipe in order to do the plugs on the 4.0, so I suspected that the EGR was involved in the stalling/lean condition. Today I decided to clean the EGR valve, and when I was taking it apart, I *think* I found the cause. I removed both EGR mounting bolts partway, and I noticed that the EGR valve gasket was not attached on one side. The bolts go thru the gasket, so unless I somehow confused myself (by removing and then reinserting the bolt), that means that the EGR gasket was only partially in place...which would make it impossible to get it to seal. So I cleaned everything and reassembled with a new gasket.

Now, these kinds of codes are notorious for "I fixed it! Oh wait...no...it's back..." So I'm not declaring victory yet, but I did notice that the short term idle fuel trim looked very good on first startup. Previously, it had been horrendous: +25 to +35%. Now it's more like -5% to 5%. So there's hope!

After reading your statement about stalling and live data. Did you check the coolant temperature sensor temperature? When a CTS fail it cause running and idling problem. The PCM does not know how to set the correct fuel mixture. The use open loop values vs closed loop dats.

 

[lobo411]

After reading your statement about stalling and live data. Did you check the coolant temperature sensor temperature? When a CTS fail it cause running and idling problem. The PCM does not know how to set the correct fuel mixture. The use open loop values vs closed loop dats.

Thanks for the reply! The CTS seems to be reading correctly based on scanner data, but tbh I'm planning to replace it anyway the next time I retorque the lower intake manifold gasket bolts. That should be in December '23 or January '24 (I always do it a few months before smog check, so things are as tight as can be). It's unfortunate, though...I used to be able to count on parts stores always having Explorer parts in stock. Now...Everything has to be ordered.

Anyway, the code didn't come back today, so hopefully the EGR gasket was the problem! There's still work to be done because I think it's still running lean, but the main thing is to get rid of that CEL...automatic smog check fail!

 

[lobo411]

Well I think this is fixed...Hasn't set a code since I redid the EGR gasket. Fuel trims seem OK based on this doc:

https://www.aa1car.com/library/ford_tsb_04-17-4.pdf

And I spent 30 mins idling at a city run hazmat collection event today without setting a code, so hopefully it's gone!