IAT values jumping. Car running lean.
 

A while ago, out of the blue, the AFRs would oscillate between 14 and 22 at idle. It did this for a few minutes, then it went away. It happened again on several more occasions. It seems to happen in particular if I do a few hard runs to 12-14 psi or so. Applying some throthle improves things (AFR to 16), but then rapidly going up to 20’s. This situation COMES and GOES. When it goes, the car drives just fine.

So I had TS hooked up one time and noticed the manifold intake temps reading at 225F. It appears that there is a connection between the high intake temps and the lean condition.

Now onto the IAT. This morning, the temps in the intake mani were (as reported) 70F. Driving the car, it started leaning out again. I glanced at the screen, and the temp readout was still 70, but then jumping up to 180 or so, then back to 70.

questions:
1. could the lean out be caused by a faulty IAT reading?
2. i have a hard time believing that the 225F temp was real and I was experiencing heat soak. I did those runs in an ambient temp of 28F.
3. what is wrong with the IAT/connections? how do I fix it?

thanks

This sounds like a loose wire or connector at the IAT (or MAF connector). Yes, it definitely could make the ECU pull fuel if it thinks the air density has dropped.

thanks, Matt. It is definitely the IAT readings causing the lean condition, as there is strict correlation between the intake mani temp readings jumping around and the lean condition.

So, what happens, is that the temps are 70 F, then jump to 200-300F, then return to 70, all that within a second. Then, repeat. I recalibrated the IAT, the same.

I have the wires from the IAT connected to the MAF harness just by plugging them in. The problem is that while the car was doing the AFR fluctuations, I unplugged and replugged the wires from IAT to the MAF and the car was still doing it. Is it possible that this new IAT sensor (installed along with the turbo 500 miles ago) is bad?? What else could it be???

its because by their default IAT fuel correction it takes away fuel above 80f and never puts any back which I believe to be retarded. Personally I rather seen that ripped out and setup so it doesn't effect the fueling without putting values into the IAT fuel correction table.

In order to fix this you have to basically use the IAT fuel correction table ( MAT nonlinear correction ) to zero out any chance for IAT to alter fueling.

Watch GAIR in your logs effect GAMMAE

GAIR is the IAT correction aganist fuel
GAMMAE is all the combined corrections aganist fuel

Its to bad it would be nice if they had under and over limits which the sensor couldn't possible report correctly that way it would disable the correction based on the sensor and send out a code on a bad sensor.

this makes perfect sense. I wish I knew before changing out the fuel filter, fuel pump and furl pressure regulator.

however, the question remains if it is a bad sensor or something wrong in the MSII. i don't think it's the connection between the iat sensor and the maf harness as jiggling the wires there makes no difference. how do i diagnose the problem.
thx
florin

I would sugguest using a multimeter with it set to read resistance and see whats going on. Could be sensor is going bad or possible a bad connection at the MS.
Seening its a GM IAT i would suggest have a substitute sensor around.

this issue comes and goes. when it's gone, the car runs well. i also noticed that it tends to come back if i run the car hard. does this sound like the sensor or the MS? in other words, when these sensors go bad, HOW do they go bad? no reading? same reading all the time? working just fine most ofthe time and then giving erratic readings??

Made sure no connections are lose, either at the MAF connector or at the IAT connector. I'm not sure how the GM IAT failures usually happen. Sorry can't help past there. You could take it out and measure it in hot\cold water and see what results you get. Only other thing is a connection and when you get on the car hard its torquing the motor enough to reseat the connection somehow

again, this makes perfect sense. i will check the connections at the iat and the harness to the MS. i hope its a connection or the sensor and not something within the MS

btw which bosch ev14 injectors are you using?

When GM IAT sensors fail, they fail open, i.e. not connected at all. I've never seen one go intermittent - it's a pretty black/white thing.

I thought the GM "fail" temp was -40F? Or is that only for the MS1 cals? When I was dumb and used to leave the IAT unplugged after working on the car, it would always run pig rich. Lean is not a preferred failure mode.

AEM EMS has CLT/IAT/MAP sensor high/low parameters and a user-adjustable failsafe setting.

550

then it must be a connection (either at the iat, or at the harness at MSII, or inside the MS)

thx

did some testing this morning. i jiggled the wires at the maf harness, no change. i did the same with the wires and connector at the iat, no change. the temps shown were pegged at 70F. Then, i disconnected the harness on the MS, reconnected and the temps were now 60 and showing slow change (normal, I think) as I drove the car. Between 55 and 62, slow changes.

then i start driving the car in boost, and after not long (minutes) the temps are again 225-230. disconnecting and connecting the harness at the MS made no change.

what could this be? paging Braineak...

when it jumps to 70°F you lost the connection to the AIT.

Sounds like you still have a bad connection/solder joint.

no more jumping now after I disconnected the MS harness and reconnected. It reads between 210-230F with the engine relatively cold (coolant temp 80F).

i reasoned that the temps CAN NOT be that high, so i went into TS and "calibrated" the IAT, as follows:
48F - 3000
87F - 500
145F - 5

These values are obviously much, much smaller than what is recommended (if the IAT works well). Sure enough, now the mani temp reads between 68-85, no jumping, just slow movements according to temp variation; car driving fine.

I will test the IAT tomorrow with ice cold water and hot water and will see what it outputs. if its outputs are fine, then the only other explanation that i can figure out is something in the MS.

please correct me if I am wrong.

i took the iat out of the car and tested it.

in ice water it reads 8700 ohms
in boiling water it reads 170 ohms

are these normal values?
thanks

I'm having a similar problem on restart with the motor warm. After a couple minutes it goes away. I was attributing it to the LC-1 wideband, but I'm rethinking after reading this. I'll check the connections as Braineack and the others have indicated. Iterested in finding out more about your problem/solution.

have a datalog of a warm restart?

I can tell you what I did. I checked the IAT and that appears to be ok. See above. Then I measured the resistance of the circuit from MAF harness to the MS. I found 3100. You have to do that with the MS powered off. Then I used the 3100 value as the resistor bias in MS. The reported temps appear to be fine now and the car drives great. The recommended valur is 2490, but in my case it was different.

Not sure if what I did is the correct solution. Any input from people who know better is appreciated.