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IAC, AC or th fix

B

BrApple

No Life But CEG
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Joined
Dec 23, 2001
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Location
Gales Ferry, CT
so one things leads to another. With my SVT I was getting a high idle even with the th hang fix. After driving on the highway for an hour with the AC on the idle would hang around 1200 rpm. If I let the clutch out at 1500 rpm the rpms would increase to 2k rpm then drop to 1200 rpm. It would also do this for some time after turning the AC off or driving on local roads.

So on a whim I got some maf cleaner and cleaned the maf. after an hour drive on the highway everything was fine. the rpms would drop to the correct idle rpm of 750.

now when I use the AC the idle will drop low. It will idle around 250~500 rpm. I have to hold the rpms at 750 for it to idle right. Also the rpms drop really fast when the AC is on.

I am thinking that the TH copper cap needs a slightly larger hole. But again the rpms drop quick but nicely and it doesn't almost stall out when the AC isn't on. When its on it want to stall and can barely catch itself.

I do believe the hole in the copper cap was openned up once before.

Also isn't the AC suppose to bump up the rpm when its turned on so it will still idle correctly?

So this again is on my 2k SVT, 49k.
 
BrApple said:
...Also isn't the AC suppose to bump up the rpm when its turned on so it will still idle correctly?
...
Click to expand...
Correct.

Have you tried a new Ford IAC valve for the 2k year? Also, when you do that, you may want to remove the cap in the hose first and see what the engine is doing.
 
I'm thinking that you added the cap (and thus the hole size) when you had a dirty MAF.. so, based on a dirty MAF, the hole you drilled was fine. Then as the MAF got dirtier, the revs started hanging.

You clean the MAF, you change the calculations. You need to now re-establish the hole size.
 
I had a similar issue. I was able to postpone IAC replacement by cleaning the IAC's plunger with brake cleaner.......did this a few times for about a year but eventually replaced the IAC.
 
Tony2005 said:
Correct.

Have you tried a new Ford IAC valve for the 2k year? Also, when you do that, you may want to remove the cap in the hose first and see what the engine is doing.
Click to expand...

with 49k on the engine I wouldn't think that the IAC would be a problem. Now when you unplug the IAC with the engine running should it idle down or up? I could of sworn when I did it before the idle went up but this time it went down.

Ray said:
I'm thinking that you added the cap (and thus the hole size) when you had a dirty MAF.. so, based on a dirty MAF, the hole you drilled was fine. Then as the MAF got dirtier, the revs started hanging.

You clean the MAF, you change the calculations. You need to now re-establish the hole size.
Click to expand...

Sounds right to me. I have had the car 9 months now but obviously didn't drive it over the winder. So a month last fall and on and off since April this year. It was fine until we got into the heat of summer here in CT. That is when the idle started hanging.

Also maybe it has something to do with the slight differences between PA and CT climate wise ....
 
My 2000 does the exact same thing that yours is doing (after you cleaned the MAF). i havent started looking into it yet but im deffinitly going to keep an eye on this thread and ill let you know if i do come up with anything.

I may datalog the IAC on the way home tonight. both with and without the AC. see what the difference is.
 
striker2 said:
My 2000 does the exact same thing that yours is doing (after you cleaned the MAF). i havent started looking into it yet but im deffinitly going to keep an eye on this thread and ill let you know if i do come up with anything.

I may datalog the IAC on the way home tonight. both with and without the AC. see what the difference is.
Click to expand...


yeah I have previous IAC data logging that I need to check to see if it idled up or down when I unplugged the IAC. both my cars now idle down when I unplugged them. When the SVT was idling high unplugging the IAC didn't do anything at all to the idle.

other then that I get the classic hessitation/bucking the moment it hits 1/4 tank of gas. I sometimes think I notice it at wot even with a full tank of gas. If I only use part throttle it is fine all the way to the end of the tank. I still need to pull and check the pump and in tank filters out.
 
i would just replace the pump with the updated assembly. ill deffinitly get some datalogs this afternoon then.
 
i just cut the tabs using a razor blade. i just put the blade between the tab and the lock ring and pushed and wiggled until it cut it the tab off. the tabs are fairly soft and cut pretty easily. from there you just pull the lock ring out of the tank and drop the new assembly in.

I had installed the FSVT pump back in december (IIRC) and it only lasted about 6 months before it was doing the same thing again.
 
ok that doesn't sound as bad as I was thinking but I don't know if its something that I want to take on. guess I will have to pull the pump and take a look.
 
I was having similar issues with my 2000. This weekend I cleaned the IAC and TB. I also worked on the TH fix. All which helped. I thought it was fine, but when I turned on the AC the RPMs dropped too quick and I actually stalled out with the clutch pushed in this morning going into the office. Im considering a larger hole in the cap.
 
according to the datalog, the RPMs do indeed stay close to the desired RPM both with and without the AC on. that tells me that even with the TH fix installed, its getting enough air for idle with AC. It also means that the IAC is working properly. although it still doesnt answer why the RPMs drop so fast between shifts.
 
rpms dropping to fast is normally a th fix that is to small. so the rpms crash and the iac can't move enough air to make a stable idle. but once it reaches idle the iac can move enough air to keep an idle.
 
There are some confusing descriptions in this thread. The vehicle should not hold idle when you unplug the IAC....it should stall if you maintain a zero accel pedal postion & disconnect the IAC electrial connector.

Hopefully this helps.......

The IAC reacts to the PCM's commanded plunger position. The PCM calculates the IAC plunger postion via the accel pedal position (it looks for a zero postion) and an engine load value (electrical, AC, etc). When the plunger is opened to the appropriate setting, the IAC introduces an air charge to the intake manifold by bypassing the throttlebody (which has a closed throttle plate at idle).

IAC plungers are susceptible to "gumming" up due to oil blowback around the pistons and due to evaporative fuel/oil emissions. If your vehicle soaked for a long time (as described) in humid weather conditions, your IAC likely experienced these issues.

My suggestion if your vehicle stalls upon disconnecting the IAC electrical connector is to remove the IAC (only 2 fasteners) and clean out the plunger with a Carb cleaner. However, if RPM's spike up upon disconnecting the IAC electrical connector, then there is a different root cause ---- either a leak in the throttle body or an incorrect command to the throttle plate to open.

My guess is that its the IAC. Best of luck.
 
i pulled out the TH fix this morning before leaving for work. turned the AC on, the idle was fine (after it settled from changing the amount of air flow) and the revs didnt drop like a rock between shifts. i guess i need a larger hole in my pipe cap.
 
Brian are you going to cut the floor up to take the pump out? I would recommend getting the new redesigned module and dropping the tank. I just think cutting the floor up is kind of mickey-mouse.
 
turbo_fox said:
Brian are you going to cut the floor up to take the pump out? I would recommend getting the new redesigned module and dropping the tank. I just think cutting the floor up is kind of mickey-mouse.
Click to expand...

can go either way I suppose. I would normally suggest avoiding dropping the tank as the straps are obsolete and are normally very rusty.

but my SVT is very clean and doesn't have any rust so dropping that tank might be easier.

Greg cut the body on my Se was I was inclinded to just do that and not mess with removing the tank. But then again maybe I will see how much Ford would ask to install a new pump and do that instead. normally I wouldn't go this route but I don't really feel like messing with it at this time.
 
update on my car. I pulled the copper cap to see what would happen. nothing changed. Well the rpms dropped alot slower and I got the moose bad when reving it. It found idle fine but the rpms would drop when I turned the AC on.

So what tells the pcm that the AC is on? I suppose it could still be the IAC but with it finding idle fine, maybe alittle slow I would lean to thinking it isn't the issue.
 
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