claudebarnhart

"Fast Idle" has been the topic of other threads, but having read them all, I've started anew.

My "fast idle" problem: 1992 F150 5.0; AOD transmission, A/C, 2WD, 159,000 miles, clean truck, bought last week with new battery, new alternator, rebuilt trans, new muffler & tailpipe. It idles at about 1500-2000rpm (no tach), but too fast. Fast idle is all the time, whether in gear, Park, or Neutral; warms up fast, idle kicks down some but stays at fast idle, and somewhat rough idle, not smooth.

I bought the Equus 3145 code reader from AutoZone and checked for error codes - none - checked three different times - none.

I have replaced the idle air control valve, the MAP sensor, and the throttle body gasket (after checking for vacuum leaks with a spray can of starter fluid) and nothing has helped.

I also replaced the spark plugs, wires, distributor cap and rotor - to no avail.

I've added two cans of Lucas fuel injector clear as well, in case the injectors were dirty, but no effect so far.

This looks like a classic vacuum leak, but I can't find one; even after searching with a 3' section of hose, and with the starting fluid.

Any suggestions will be greatly appreciated.

Thanks,
Barney in Memphis

claudebarnhart

Memphis has an auto inspection that refuses to inspect a vehicle if it's idling "too fast." My F150 was idling at about 1500-2000 rpm, noticeably too fast.

When I replaced the throttle body gasket, I thought the throttle body looked newer than other parts -light comes on in thinker- so I looked in the glove box at a collection of old receipts and found that the throttle body had been replaced in connection with a "water leak" at the front of the engine in 2004, at a reputable Ford dealer.

After having read a thread at: http://www.supermotors.net/registry/media/624983 concerning the throttle plate orifice plug, I pulled off the air tubes from the air cleaner to the throttle body in order to view the throttle plate for the "orifices" referenced in the "How to adjust idle speed (official Ford procedure) at the above link. Sure enough the orifices were wide open, no plug(s) installed; and all indications were/are that this condition allowed excessive air into the intake & Bro' electronic fuel control interpreted "add fuel to this amount of air" which it did and the engine idled way too fast. How was Bro' electronic fuel control to know any better?

Somewhere I found that the "kit" containing the orifice plugs and instructions on how to set idle speed (after installation of a new throttle body) was $202.00! Bro' change purse balked and insisted on further research. Said research found a suggestion of taping over the orifices on the throttle plate and slightly cracking the throttle plate open with the idle adjustment screw might check to see if the fast idle was dependent on the overly large orifice openings.

First problem was how to tape over the orifices which are 6-7" back into the throttle body tubes. Problem solved: I used a pair of long hemostats to hold a 3/4" square piece of "duct tape" so that I could extend the piece of tape back into the tube to the orifice. I used a nice new pencil (eraser end) to tamp the duct tape securely over the orifices.

With the orifices blocked, I used the idle adjustment screw to let the throttle plate close completely; and started the engine. Start was instant and after an initial start-up fast idle, the idle backed way down - no tach to tell exactly, but what seemed like 700-800 rpm.

I then removed the negative terminal from the battery for ten (10) minutes to clear the computer's memory. After the ten minutes, I hooked the battery back up, drove the truck for ten miles to let the computer collect its thoughts about idle mixture and whatever else it wanted to sense, and then drove directly to the city inspection where under normal idle the truck passed with flying colors - no CO2 emissions, and negligible other pollutants.

My next project will be to find a way to better plug the orifices, than with the present duct tape. I've thought of using either a small brass or plastic screw to just screw into the orifices and let that be the repair. Any other ideas?

It seemed obvious to me that Bro' reputable Ford dealer had installed the new throttle body, but had failed to adjust the idle according to official Ford procedure; and that the truck had been idling fast since 2004. In the interim, the previous owner became disenchanted with the truck as he seemed to be having trouble with the transmission (fast idle, shift points, Bro' transmission confused between engine speed and road speed and shifted too often and at seemingly wrong times); and he had the transmission rebuilt ($900). Most probably the previous owner would still be driving this F150 if Bro' Ford dealer's service department had just set the idle properly after replacing the throttle body; he would not be out the $900 for a transmission rebuild; and he would still be driving a reliable vehicle. Bro' transmission rebuilder can also not be forgiven in this debacle as most would think him responsible for setting a normal idle speed to help his rebuilt transmission perform as advertised.

More later, if any thing earth shattering develops....

Barney, in Memphis

Just call me Sean

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Go to the junk yard and get the plugs from a donor.

claudebarnhart

FOUND: Another vacuum leak, by using the starting fluid, and a friend who has better hearing than I. The leak was at the front end of the intake plenum - a 2" gasket section was gone!

This is another classic story of a lotta work to replace a $6.99 gasket; but, the gasket did the trick, and the truck now idles normally - with the duct tape still covering the small holes in each throttle plate (in the throttle body).

Another symptom that there was a vacuum leak: the brake pedal, once applied at at light or stop sign wanted to lose it's pressure and wasn't as stiff as normal. First thought was to check the vacuum brake booster, but when pulling the hose and plug out of the booster, a big hiss indicated that the brake booster was holding vacuum and not leaking. Brake pedal pressure back to normal after replacing the plenum gasket.

Rmike

Dude you could use a grammar coach.
Fingerprints are took? days is lost?
Dammmm-- you talk like a CEO!

But-- if you is a motor fixer, then that are cool

Just call me Sean

iTrader: (1)