If I'm creeping in gear without my foot on the throttle and put the clutch in, the revs jump above 1000 and then return to idle at about 750. It also seems like it's slow to return to idle. What's going on? Is this the flywheel's effect, or what? It's really irritating. Embarrasing, really, because it makes it sound like I don't know how to drive, know what I'm saying?
I just got my truck, it's a 99 XLT 4x4 4.6 5 spd.
Thanks
J

 

what's the spec for idle with a manual transmission? 650 rpm?

 

Hi jb'sghost and welcome to FTE

The spec that I can find for idle speed says 680-830.
You could have a lazy IAC (idle air control) or maybe a vacuum leak. Sometimes a bad TPS will cause a high idle.
I think that if you cant find a vacuum leak you should probably get the truck scanned for trouble codes to lead you in the right direction.

 

Hi,

I may actually have a contribution that may help explain this phenomenon.

First some past info that I posted in another thead and notes about my vehicle. I own a 2003 4 X 4 4.6 V8 5 speed man. Sooo, the control chips etc. may be a bit different.

I have noticed that as I slow down and depress the clutch the tach will stay at 850 RPM until the truck is very close to stopped. I presume some sort of air pollution measure. The chip is smart enough to monitor speed and not return the engine to idle (750 RPM) until the vehicle is stopped (really at about 1 or 2 MPH).

The engine and I presume the control chip is always trying to maintain some given set point. Usually idle (assuming no throtle depression). Sooo, if you are creeping along and the creep keeps the engine RPM slower than 750 or perhaps 850, as soon as you depress the clutch, the engine trys to return to idle but since it is in the position of trying to get their, it over compensates and overshoots the mark.

You should be able to reproduce this effect by leaving out the clutch when stopped a bit too quickly, slowing the idle to less than 750 and then quickly depressing the clutch. The idle will overshoot the 750 mark.

I also find that since such a very light touch on the accelerator pedal causes a almost instant high RPM my starts from 1st gear often are not as perfect as in the past.

I find driving the 5 speed almost a challenge compared to the simpler carbureted cars of past. I suspect yet another reason why for 2004, the F150 will not have a manual transmission offered.

I have to wonder if sports cars with 5/6 speeds have figured out how to build the computer chips to make the drivers job easier not more difficult.

On a slightly different thought. I find that the hydraulic clutch used in the last 20 years or so instead of the steel straight connection offers little feel to the driver. With the straight connection one could actually feel the clutch engaging, now one must look for other clues such as the vehicle moving or the tach losing RPMs. Again, a bit more of a challenge.

If your buddy in the drivers side thinks you are losing it. Ask him to try to do better. S/he will soon praise your driving ability.

Chip

 

Good points charlesh
The idle does come down a bit slow to help emissions. Normally though I dont think it should go above 1000 rpm like J's is doing.
I dont work on all that many trucks with 5 speeds but next time I do I'll pay a bit more attention to how it works.

 

I noticed today that when I'm driving normally and depress the clutch to change gears, the revs jump too. So if I shift at, say, 2750 rpm, the tach may jump to 3500. I am taking my foot off the throttle at the same time I depress the clutch, so the rpms should drop, not rise. This is frustrating, because it takes longer for the gears to synchronize. I guess I will be visiting the garage soon.

 

Opps,

It is obvious that though I thought I had some good hints on the workings of the modern engine and the interaction with a manual, it sounds like you do indeed have a problem.

Maybe Racerguy could help. Sounds like the throttle body butterfly is hanging up or the throttle cable is getting hung up. I have a Toyota with 250k and the local machanic wanted about $800 to replace the throttle body. I balked and started my own search for why the idle was not returning to set point. Turns out (don't ask how long it took me to get to the bottom of it) that the cable was hung up on the sheath where it attached to the accelerator pedal.

Good luck. Let us know the fix.

 

After some shadetree diagnosis (my own) I decided to replace the IAC valve. $65 from my dealer. It fixed the problem. My truck now returns to idle smoothly when I disengage the clutch.

 

Thanks for letting us know what fixed it