High Idle 4500 RPM

"maxpower" wrote in news: snipped-for-privacy@comcast.com:

Touche' :D

What I meant was is that when I am am drive and and not giving it any gas, I estimate my speed at approx 40mph hehehehehe

Would a single leak cause the excessive idle? Or would it be more likely several leaks?

Thanx for the assist.

Michale

Except that opening the throttle also calls for more gas to be injected. Adding air alone will only lean the mixture. You might get a little bump in RPM, but you shouldn't get 4500 unless way too much fuel is also being injected along with the air leak.

It sounds like something more fundamental than an air leak is involved with his problem. Beats me what, though.

Have you checked for a malfunction code in the ECM?

Matt

Why on earth would you put the car in Drive with it idling that fast? The lurch in to drive could easily break motor/trans mounts or worse. Stopping the car with the engine running that fast will burn up your transmission in short order.

The brake booster is one large vacuum hose. With your idle speed I dont have a beter suggestion for you on where to start looking for the leak, but wherever it is it is one heck of a leak and should be pretty easy to find. Also make sure that you haven't somehow blocked the throttle partially open. If you can look down in the throttle body the blades should be almost closed.

Steve B.

Last I knew, the TPS sensor was also factored into the fuel map for ECM controlled vehicles. Maybe Chrysler was really stupid with their ECM, but I doubt it. If the throttle is closed as indicated by the TPS, then I'd be really surprised if the MAP input alone would be enough to command fuel be added. If that is the case, then the TPS is completely unnecessary.

Matt

I don't think Chrysler publishes its ECM algorithms, but I've be very surprised if the TPS is used only to sense closed and WOT. If that were the case, they would use two cheap switches rather than a relatively expensive rheostat sensor. I'd also be very surprised if they don't make a check for closed throttle when the MAP is indicating low pressure and thus calling for more fuel and not rev the engine wildly with a closed throttle. Maybe the Chrysler engineers aren't that smart, but I'm betting they are.

Have you ever seen a Chrysler engine have a vacuum leak that made it run

4,500 RPM with the throttle closed?

Matt

~Excluding transmission/transaxle functions~ Rate of change in order to increase the injector pulse width when the throttle is opened. Idle air control valve diagnostics (fault sensing) The TPS is the least important of all the input sensors, its biggest effect on fuel delivery is when the PCM is receiving a changing voltage from it indicating throttle movement.

Some manufactures have been known to do this.

Closed throttle low MAP pressure is a heavy decel, which is a whole different situation from the potential mass vacuum leak being discussed. A vacuum leak that can/does add hundreds of RPM to idle speed

-raises- manifold absolute pressure, raising manifold pressure is usually responded to by the PCM by as an increased injector pulse width.

Some things are beyond the limits of control of the system.

You've got a minivan or two at your disposal... Hook up your scanner, pull the PCV or brake booster hose off, start the engine and report back with the results, i.e., RPM changes, MAP changes, pulse width changes. You may not see 4500 RPM exactly, but you will experience the causes and effect.

Also, with switches, it is a mechanical adjustment (provisions for adjustment and the labor of doing so) to calibrate the closed and WOT positions - cost would more than offset the cost of the rheostat. With a rheostat, the calibrations for the two points are software functions, and possibly 100% automatic (I would think it would be easy for the computer, during the learning phase to tell where the throttle closed position - i.e., the point below which the rheostat never goes), and the WOT position could be delta'd off of that with acceptable tolerance stack and variations - though not sure if they actually incorporate such an Al-Gore-ithm).

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

Much obliged for all the information and tips.

Little more information. The RPMS have settled down into the 3000-3500 range.

There is an opening in the EGR hose that I still need to get fixed.

ERROR CODES:

12- No biggie on this one, the battery was recently disconnected and re- connected.

24- Throttle Position Sensor

25- Idle Air Control Valve Circuits

I have an Ohm Meter and can check the voltages on them if possible. Not sure the general procedure or readings, though.

Thanx again.