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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

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Old 11-03-2009, 11:52 AM
muddydawg muddydawg is offline
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351W cold idle / fast idle

Hello all,
Well I have spent some time going over many threads on this site and it is very informing but I have yet to find the answer.
As it seems to be a problem many are having I feel mine is a little different.
Just picked up this truck and it's in great shape, even the motor is new since PO changed it out with a crate motor which now has 5000 miles on it.
Now my problem is the truck runs like a champ once warm but will not idle on it's own when cold.
I removed the IAC and verified it's movement. The solenoid will not move full stroke even when I jumper it directly to the battery. Removing the connector during hot idle does not change RPM as mentioned in other threads.
Pulled the codes and only got 552 KOEO and 412 KOER. Looked around for vacuum hose problems and none found.
I tried a new IAC and the engine revs high maybe even very high and never settles down even once the engine is at temp. I have no Tach so I can't say what RPM.
Re-installed the old IAC and everything runs normal except for no cold idle condition.
Now my question, since I found nowhere a mention that I should reset the EEC after replacing the IAC I was wondering if that would have been the missing step in this procedure.
Every little bit of anti-pollution and canisters all check out since they were either replaced or reconditioned during the engine change.
TPS sensor ohms out within spec stated on Ford Fuel Injection.
I have not verified ACT or ECT as of yet. I think the ECT sensor is in front mounted on or near the thermostat but have yet to find the ACT anywhere.
I do not suspect those parts for the time being due to the fact that fast idle occurs upon changing the IAC though fast idle conditions don't go away and with the old one it runs great.
Any ideas?
Thanks!
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Old 11-03-2009, 01:41 PM
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andym andym is offline
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Sounds like you have a vacuum leak. Do you have a vacuum gauge?
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Old 11-03-2009, 11:23 PM
muddydawg muddydawg is offline
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No it's one of the things missing in the tool box.

I agree that it sounds like a vacuum leak but how do you explain the high RPM with the new IAC and not the old one?

Do you have to reset the EEC anytime you change a sensor or actuator?

Thanks for your advice, I will get one since it seems we need one quite often.
Not used to this fancy FI.
By the look of things I will be doing a lot of reading here.

My other vehicles are easier to work on.
The trail machine is a CJ7 360 swap w/ T18A Dana 20 and the daily is a Legacy GT. The F-250 is now the toy hauler.

Thanks again.
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Old 11-04-2009, 10:30 AM
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The plastic vacuum lines are well known to be brittle and leak. In most cases a vacuum gauge alone will not show the true story. I used a hand held vacuum pump/gauge to test each vacuum circuit independently on my '92 F350. Most of the plastic lines we toast. I replaced each of them as well as all the rubber lines. My "coffee can" reservoir behind the driver's side headlight was rusted through. I also found the PO had attempted to repair the vacuum reservoir on the blow motor/evaporator case, but failed miserably. Once I fixed all those leaks my truck idled much better, but still a little on the high side. I ended up also replacing the gasket between the upper and lower intake manifold. Now all is good. I did test my idle vacuum before and after replacing all these pieces. With all the leaks it was ~15" warm, after all the leaks repaired ~16.5". Both are in range, but now the idle RPM is correct.

You stated your TPS measured the correct ohms, but did you measure the voltage at idle? I always remove the power to the EEC after changing any sensor. That will erase any long-term fuel trim adjustments the PCM may have stored.
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Old 11-04-2009, 04:12 PM
muddydawg muddydawg is offline
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Thanks RLA

I'll triple check the vacuum lines, as for the gasket I mentioned in my previous post that this is a new crate motor that was installed just 5000 miles ago and all the gaskets are new including new exhaust manifolds.
The PO used the original intake and such since he striped the old block to install the new one.

You mentioned to reset the ECC when a sensor was changed, is it the same for actuators?
Remember the motor runs great with the old IAC except for no fast idle on cold mornings and with a new IAC it runs fast and never comes down to a regular idle.

I will look at the voltages from the TPS sensor as soon as possible, I need to finish overhauling the cab for my payloader before our 1st snowfall which should be coming soon.
I just have a hard time believing the TPS could be out of whack when it idles perfect once warm and pulls great even under heavy load.

I don't know much of these 1st generation FI systems since the Jeep is carbed and for the Subaru I have a ECUTEK programmer which gives me the problem and solution.
Thanks for your feedback.
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Old 11-04-2009, 04:19 PM
muddydawg muddydawg is offline
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Sorry about the repost.
As for the coffee can behind the drivers headlight, I do not have one, I do though have a plastic one like a coffee can (passenger side) and an other one right next to it which has the red and white hoses going to it.

Hope that helps.
Thanks,
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Old 11-04-2009, 04:27 PM
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check all your vaccuum lines and replace both the "coffee cans" that should help your problem
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Old 11-04-2009, 05:01 PM
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Use a vacuum pump/gauge to determine the integrity of the reservoirs before replacing them. Of course a thorough visual check is needed too. No sense replacing something for no good reason.
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Old 11-04-2009, 05:01 PM
 
 
 
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