Need help. Erratic idle. About a month ago, when coming to a complete stop, the engine RPM's jumped to aprox. 1100 causing the truck to learch forward (almost into the back of the car ahead). This would happen occasionally. I replaced the IAC, MAS removed and cleaned the throttlebody, intake runner, EGR, PCV. This problem has not returned. The next problem has existed prior to the erratic idle and has both of the Ford Dealerships puzzled. They want me to drive the truck until something breaks. One of the dealers thinks the converter clutch is not releasing (even though the high rpm happens in PARK). Their are no error codes. When coming to a stop from average driving, the RPM seems very high (850-1100). This causes the truck to continue to pull for a few seconds, then the idle slows to normal (580-600) and all is well. If I put the trans in neutral while the truck is pulling at idle the RPM's jump to about 1100 for a few seconds. This happens more frequently after the engine temp is at normal and the outside temp is above 90. Have noticed when at idle (for 15-25 minutes) in park the engine idle creeps up to between 900-1000rpm's. It will continue to idle high until I drive for a few blocks, then the idle returns to normal. Generally the truck drives and shifts normally, gas mileage is still about 16 in town with air and 23 on the road with cruise. Can not find any vacuum leak, or air leak in the intake system. If I set the cruise control to 30 MPH the truck will not maintain a level speed, it increases and decreases speed to the point where the cruise turns itself off. I can not maintain a steady speed with the accelerator on level ground. If cruise is on and going down a hill the vehicle speed continues to increase to where I have to brake to keep from running over someone. Have had very little trouble with the truck, engine oil changes at 6K, trans flush at 20K. The truck has 62k and always starts and runs all day long. No hesitation, always has power when needed. This is a service vehicle at work and makes 8-10 service calls a day.
Any help work be greatly appreciated.

 

You might try disconnecting the cruise control cable at the throttle lever to see if the problem goes away. Maybe it is engaging slightly on its own for some reason.

HiO

 

Hey, HiO,
Yes I thought of that a while back, it made no difference. I have tried disconnecting the following while at idle to see the response:
MAS==no change
IAC==no change
EGR Vac. source==no change
unplug TP==no change
plugged PCV line to intake== idle did change a little(became more stable)>>>replaced PCV(new)==no change
unplugged temp sensor==no change

I am becoming annoyed with this truck now. This morning when I used it , I had no problems. When I went for a drive this PM and after it warmed up it started the same thing all over again. I did notice this time that when it started it's idle-up routine, when I approached the stop, I put the trans in neutral to see what would happen. The RPM's shot up to 1100-1200 for 2 seconds, then slowly drop to 850 then slowly to 625 where it would stay.
When I put the truck in gear the RPM would drop to 580-600, and be OK until I had driven at a constant speed for a few blocks.

HELP,,
Losing cool.

 

Have you tried just disconnecting the battery for about 15 minutes?

When you start it back up, let it idle for about 20 minutes.

You could try wiggling the harness to the computer to see there any changes or just unplug the computer harness and see if there any corroded contacts.

Have you done any mods like K&N filter etc...? What year truck, what engine?

 

Hey, canyonslicker.
Thanks for the return. I have a 2001 supercrew with the 5.4L Triton. I put Amsoil, K&N, and Flowmaster on the truck at 5K. It now has 63K. Have had no problems at all till now. I have had the battery disconnected a number of times, as recently as 62K when I clean the throttle body, MAS, IAC, EGR, intake, replaced PCV, IAC, MAS and checked all vacuum hoses for leaks. I have not played with the "BRAIN" as of this date. Today I went back to work after vacation (Charlie and Francis). The truck performed flawlessly today, no problems at all. But the outside temp did not get above 90 degrees so that may be a factor.
Andy.....

 

Glad to read that people are experiancing the same issue as I am. The temperature has suddenly dropped here in colorado and we did not get out of the low 40's in my town yesterday. I came to a stop at a light and the engine reved up with my foot on the brake...I lurched forward and thought that someone hit me from behind.

Now still today temp is only 50 degrees and in park the truck goes up to 1200 rpm, then down to 900, then to about 650 where it usually idles. Does this once every 1 to 3 minutes.

I am reading the suggestions here but since none appear to be working I'll hold off.

Does anyone know any other ideas to resolve the issue?
--Justin