1995 f-150 high idle/no shift problem

I would start by a good cleaning of the IAC. Remove it and soak the valve end in a good carb or throttle body solvent over night. The solenoid can be removed easily and just drop the valve in the cleaner. Rinse and blow out good before reinstalling.

Next, give the MAF sensor a good cleaning. I believe the '95 was the year it went to MAF. If it has one, it is in the air intake tube between the air cleaner and the engine. You will need a security torx bit to remove it.. They can be gad for $5-10/set at most parts stores. Clean it with a cotton swab and a residue free electronic cleaner. Reset the ECM by disconnecting the battery neg cable for 10-15 minutes. Start the truck without touching a thing and let it idle 5-10 minutes. Move the shift selector among each position allowing it to stabilize before goingto the next so it can re-learn it's idle. It should settle in after drivig a few miles.

This may not fix it but, it very well may at a cheap price. If it does notm your next best step is a good diagnostic scan by a competent tech. A diag scan does a lot more than just read the fault codes as is the case with the free service from Autozone. A good scan should pick up out of range values that do not set a fault code. It will be far cheaper than just throwing parts at it until one sticks.

Lugnut

When the complaint is increased idle it seems logical to first attack the IAC but even tho this can be the culpret, it seldom is. Do it anyway, you prolly need a new gasket. And cleaning the MAF is also to be done as part of the normal tune up. Get the MAF cleaner spray product and allow some to soak on the electrods for a few seconds, not till it eveaporates but it will abyway so start engine ad spray on electrods as engine runs. You have to remove the MAF part of the air duct from the air filter housing to spray the cleaner into the sensor. I don't think you need cotton swabs nor have I ever heard this advice before. Maybe it helps. I've been able to clean the MAF with the spary with no problems. A can lasts for 3 or 4 cleanings. After all this the problem will still be there even tho the engine will now run better.

The problem is the EGR passages under the throttle body. They are clogged with oily, tar like substance than can not be removed without disassembly. You need the gasket for the throttle body to the manifold. They may sell you 2 and that's OK, the second one is really cheap, You'll Prolly remove the IAC to get at it so do this at the same time (by the way, if the problem really is the IAC, you usually need a new one). You can use throttle body cleaner or the rest of that can of MAF cleaner you brought. Wooden or plastic scrappers will also help because the tar substance is very thick and stuborn. Once you have the throttle body off and see inside there it will become much clearer what is going on.

I've had a '95 Crown Vic for about 4 years, it should be very similar. My Ford has 335K on it but the Ford rebuilt engine has on it only

153K. Hope this helps.

disston

Your comments are good for the 4.6L in your '95 CV which is not the same animal as the 5.0L in the OP's '95 F150. The EGR is an entirely different config. There may be a problem with the TPS which may not be picked up by the ECM, but, I would start with the simplest and cheapest things.

Lugnut

Did this, no change in problems. Tried another IAC from a good running truck (kind neighbor), same thing. I now have the truck, and noticed that it will shift out of low if you accelerate fairly hard, and at the shift point, the check engine light goes out, but comes back on again after about one second. Went to Autozone for scan, of course it didn't malfunction on the way there, so no codes showed up.

Will do this tomorrow.

Bypass Air Idle Speed Control? Is this another possible culprit, as I've read this controls the IAC.

Otherwise, I'll take it in and have a proper scan done by the dealer, although I'm guessing it'll cost more than whatever component it may need. Any ideas on the cost of this scan? Dealer will not be open until Monday.

Forgot most important thing. Pulled plug from IAC and no change in idle speed, but can't find any vacuum leaks. New PCV valve.

On Fri, 20 Mar 2009 19:24:53 -0400, Steve Walker wrote:

Most shops and dealers are in the $80-$100 range for a proper scan. A professional level scanner/tester will run the engine and trans through it's paces several repititions looking for an out od spec signal. There are several things that can give your symptoms. The trans in your truck is electronically controlled by the ECM. Unless the engine is operating correctly, it is not possible for the trans to work right. Usually, the O/D light on the shift selector will flash if the problem is the trans. One item that can give idle problems without setting a fault code is the TPS. If it is really getting bad, it can sometimes be found with an analog meter with a needle. The voltage output should range from about 0.5 VDC to about 4.75-5.0vdc. You can read the impedance the same way. Open the throttle very slowly while watching the the needle. Any sudden change or glitch in the reading indicates a bad spot. It is nothing more than an old fashion potentiometer. Another frequent failure on them is the ECT (engine coolant temp sensor) located in the water pipe from the intake to the throttle body. There charts around the net that have impedance readings at various temperatures. IIRC, it should have about .4-.6 ohm at 190 deg engine temp - 30-32 at room temp IIRC. Sorry, I don't have these charts handy. They should still be somewhere on the net. It is quite normal to see them off by one step and the vehicle run decently - not optimal. These are the kinds of things the Ford STAR tester routinely checks. Again, this is a relatively cheap sensor and easily checked with a DVOM.

Another point to chack on the 5.0L is for vacuum leakage between the upper and lower intake manifolds. They sometimes suck in the gasket. You should be able to find that by spraying a bit of WD40 or carb cleaner around the gasket. Do not use ether or starting fluid. It is much too flammable and can flash back before you know it. It is also rough on the engine if there is a laek and it sucks it in.

Lugnut

Got some codes the old fashioned way. Jumper wire & count flashes. Did Key On Engine Off test after warmup. 1st code 121. Then continuous codes of 124 and 327. Checked TPS and it's bad. Removed throttle body, soaked screws for 3 hours with PB blaster, and promptly broke one off. Damn. Gonna have to take it to work & machine it out, and maybe the other one too. Haven't tried that one. Throttle body is really gummed/carboned up, and upper intake where EGR goes in is pretty badly caked. Sticker on throttle body says not to clean. If I remove the TPS and IAC valve, I should be able to dunk it, shouldn't I? Or is the shaft bushed or sealed with something the carb cleaner will eat up? I'll clean out the EGR passage as best I can without removing the upper plenum.

The throttle body has a yellow coating of some sort that retards varnish buildup. Many solvents will damage it. Some people use a scraper to clean it which is not good. A good throttle body or carb cleaner with the help of an old toothbrush or similar device will usually get it clean. It needs cleaning in ant case. If you damage the coating, it will just need cleaning more often. If you have access to it, the foaming stuff that Ford sells is pretty good. If your TB is too badly corroded, it may be cost effective to just replace it especially if the shaft bores are worn.

If there is enough corrosion to prevent removal of the screws, the condition of the TPS is not surprising. It will do strange things with a bad TPS and the ECM may not record a fault. It does a system check with closed throttle as the engine is started. If the idle position is OK, all other positions are just linear relavant readings. The TPS should be about .5 volts base and increase linearly up to about 75% throttle. From there on up to full open, the reading should be 4.75-5.0vdc. I don't recall seeing one go all the way to

5.0vdc for some reason. From there it really doesn't matter because the system is back into open loop program tables for full power anyway.

Lugnut

Drilled out & repaired broken screw. Bushings are good. Cleaned with TB cleaner & stiff toothbrush. Cleaned out EGR passage in upper plenum. Cleaned MAF . (Just sprayed, as the wires looked pretty fragile.) Had bettery disconnected all day, and it started right up, rough idle for about a minute or two, then smoothed right out. Driveability is excellent after about a half hour of around town driving, and a 10 minute stint on the highway. Truck seems to be all cured, (good shifting, no excessive high idle) except idle is about 750. No vacuum leaks that I can find. I'll let him drive it a while and see how it acts. The IAC I put on it was not exactly the same, it came from a Salvage yard 90 something Crown Vic with a 5.0. I'll talk him into a new correct one when he can afford it. Thank you VERY much for all your help.

You are quite welcome to any help you found in my meandering thoughts. I wish I could say I have all the answers as much as I have worked with them. Unfortunately, I only have the OTJ experience and whatever I could learn by reading over the years. I am glad your were able to get it going and greatly appreciate your feedback. BTW, your idle is about as close as you will get to specs at 750. There is a range but, I believe 750 is the spec. In any case, the ECM controls the idle speed. You cannot adjust the idle except for the base idle which requires you follow the correct procedure. Adjusting the idle speed screw also changes the base voltage signal from the TPS. This can easily screw up trans shifting especially if you are at 1.0 VDC or higher at idle. That is where the spark and fuel curve get started. It sounds like you are at the leave it point unless there is a good reason to continue. If you adjust the base idle screw, the ECM will simply start looking for a way to get the speed it wants. That is not good.

Lugnut