Engine Rev Up - Ford 460

[Retired and Happy]

Returning home Monday from Mobile, we started up the northbound side of the "Dolly Parton" bridge on I-65. As we neared the top, I thought it we were going a lot slower than on my previous trip a few weeks ago. We made it to the top at 35 mph, vs the 50 or so on the earlier trip.

Going down the other side, it acted as if the cruise control were on, but I had not used cruise yet. Further down the steep bridge, I thought the accelerator was stuck, but the gas pedal acted normally. I just couldn't get the engine to slow down as it was rev-ed up pretty high...like I was in too low a gear. And the "check engine" light was on.

I used the brakes for control until we got to the north end of the bridge/causeway, and we exited into a Shell station with a large truck lot. I shut off the engine and it bumped to a stop. For about an hour I checked the oil and water and watched the action of the accelerator cables. I could start the engine and it would idle well until I touched the gas pedal, reving to around 2500, then something would take over and rev up over 4000rpm. I had to shut it off to stop it. The gas cables seemed to be operating normally, returning to the proper position when I released the gas pedal. After about the hour or so, it stopped acting up and everything was fine. I tested it for another 15 minutes and could not get it to act up again.

I buttoned up the dog house and we continued to Stone Mountain without further incident.

I wanted to clean or lube something, but there is a sticker on the housing at the air intake not to do either, that there is a special coating on the parts that does not need to be cleaned or lubed.

I know it's difficult to analyze when the problem is not happening, but... Is this going to happen again? Is there anything special I can check? Was it a one time occurrence of some speck getting in the wrong place at the wrong time and working itself out?

[RustyJC]

If the "check engine" light was on, you hopefully have a code stored in the OBD (on board diagnostics) that will give you a clue. Not being a 460 expert, I can't offer anything specific, but it certainly sounds like it could be a throttle position sensor problem assuming this engine is fuel injected.

Rusty

[tderonne]

Sounds like the Idle Air Control valve may have been stuck? Unlike the throttle body, they can be carefully cleaned.

First thing to do is check for codes. It may have found the stuck IAC and set a code for it.

Should be able to replace it fairly cheaply too, that may be a better long term cure. It may have been a transient thing too, a piece or carbon that has gone on it's happy way now.

How many miles do you have? Burn much oil? (Thinking what the PCV system is working against, how cruddy the intake may be...)

[LVJ58]

Ken, for the engine to rev up as you describe, the air intake butterfly must open fully on your throttle body. The TPS along with the MAS sends signals to the ECM which in turn controls fuel mixture. I would suspect your cruise control servo is engaging and opening the air intake butterfly causing the high revving of your engine. Try disconnecting the cruise control cable at the throttle body if you can and see if the problem persists.

Good luck and let us know what you discover, Jim

[Retired House Husband]

Hi Ken, I believe tderonne give you good advice. The Idle Air Control mounts on the lower front of the throttle body, and is subject to malfunction on older engines. It's inexpensive and easy to change.

A side note to LVJ58. Us poor folks with 460 engines don't have MAS. That was reserved for the high rollers with V10s. GRIN.

[Retired and Happy]

Thanks everyone for the suggestions. When it warms up here for more than a day or so, I will pursue this and check for some codes. I'll post back and let you know if anything showed up.