Runaway RPM

[Harrry]

I don't think "spreading" is an accurate description, but I hear you regarding an ATX issue. So let me ask you all this:

If it's an ATX issue, what would be going wrong with the ATX that would make the engine want to runaway, and to maintain the runaway once the ATX is shifted into neutral/park? This doesn't make sense to me.

Remember, the ATX performs as-advertised, except at high RPMs at highway speeds, where it *sometimes* hesitates to make the final shift (but eventually does when pedal demand is eliminated). Personally, I wonder if the engine misbehaving is causing the ATX to misread the shift cue. As in, the engine's doing 4k RPM, so the ATX thinks you need torque vs speed, and hesitates to give you the final gear.

I dunno...

Okay...TCU transmission control unit TCU... Transmission solenoids..work with the pcm to calculate when and how to shift the transmission.
Solenoids are key to telling the pcm what to do. Seeing these very units control the shifting points in your automobile...i can only see that 1 solenoid going bad could have been your final drive solenoid. Which only means now it another one might be going bad.....or worse your pcm is going bad...which is causing the solenoids to not be reading each other correctly. Thus creating a mutiple effect problem.

Please take the time to visit a dealership and pay for a diagnostic check! It will be around $75-125. That way...you will have an in car diagnostic check while the car is being driven. That way the symptom can be read by the tool so your problem could be found!

Don't start dumping tons of money in different areas trying to find this very problem. Been there done that...:blackeye:
But...it seems that is my diagnoses.

 

[Smalls]

Slow down buddy, mine would rev up and then something would happen and then the rpms would go to normal. I read enough to hear his symtoms, so before you haul off Harrry, why don't you give the advice a chance. I had the exact same symtoms the OP is having.


Have you swapped TPS's with one that works or a new one just to test if you have the same issue?

x2 i had identical symptoms as the OP and i definitely 100% had bad intake gaskets

 

[NJCSVT]

Hey guys, my first post here...yeah OP i've faced the exact same problem on my 98.5 SVT (MTX of course) in the past three weeks. It seems to get worse in higher heat and humidity. A few times I've actually had the RPM's stick at 4500!

I've noticed occasionally the rpms will hang as i coast to a stop in neutral, but when i come to a complete stop they'll go down to the regular idle. I don't know if its related but i also had my PCM and fuel pump replaced last winter because my car would crank but not start...I'm taking it to Ford for a diagnosis soon and I'll report back what they find...I'm hoping all my issues don't turn out to be wiring harness related.

 

[jsark]

Thanks, NJC. I'm very interested to know what's discovered.

In the interim, I'm tempted to pick up a new TPS ($60) and install it just as a shot in the dark. Haven't made up my mind yet.

 

[Tony2005]

... Don't understand why changing the IAC made the runaways temporarily disappear.

..Any ideas?

PCM relearning. Your problem sounds electrical or electronic.

Check the Engine Coolant Temperature sensor and TPS (and its associated wiring, including the wiring for the IAC valve, MLPS and VSS).

 

[NJCSVT]

I did find this on autobuyguide.com:

1998 Ford CONTOUR Recall ID from NHTSA: 99V194000
Auto Recall Date: 07/20/1999
Vehicle Component: VEHICLE SPEED CONTROL
Estimated Vehicles Affected: 159565
1998 FORD CONTOUR Defect Summary:
VEHICLE DESCRIPTION: PASSENGER VEHICLES. THE ACCELERATOR CABLE MAY HAVE BEEN MANUFACTURED WITH A BURR ON OR NEAR THE END OF THE CABLE SLEEVE INTERIOR. THIS BURR COULD FRAY THE CORE WIRE RESULTING IN THE ACCELERATOR NOT RETURNING TO IDLE WHEN THE ACCELERATOR IS RELEASED.
Defect Consequence:
THIS CONDITION CAN RESULT IN THE THROTTLE STICKING, BINDING, OR CAUSING HIGH ENGINE RPM.
Remedy:
DEALERS WILL INSTALL A REVISED ACCELERATOR CABLE THAT HAS A FLARED CONDUIT SLEEVE END AND MOLDED ON END FITTING.
Notes: FORD MOTOR COMPANY, 99S19

Not sure if it's our problem but I figured it would be good to know jsark.

 

[jsark]

Very interesting. Thanks for that.

I would up installing a new TPS last night. Will report back after I've driven it for a day or so.

 

[NJCSVT]

I'm taking it to Ford tomorrow and I'll let you know what they say.

Like jsark my car has been having the issue mostly during the hottest mid day hours during my commute to work...in cooler temps the car seems to work normally.

I have a bad feeling Tony's right and they're going to come back with a wire harness diagnosis.

 

[Dan the rug man]

Codes

Codes

holy crap. i cant believe no one told this guy to check his intake gaskets... spray carb cleaner or a similar product around the gaskets and listen for any surges or changes in rpm

I would agree with Smalls about the intake gaskets. I had tried the spray cleaner 3-4 times to no avail. Problem fixed with intake gaskets.
More importantly, No one has asked if he is throwing any codes. Everyone is throwing mud at the problem hoping something sticks. I thought the main reason for the codes is that you can make a systematic check of the problems with out wasting money. I generally like to do the cheap fixes first also. But if you are not correcting the problem the cheaper fixes can become expensive quickly. So post the codes so all the great minds on this site can give you the full benefit of their combined knowledge.

 

[jsark]

Good news (let's hope it stays that way):

Car's been driven three full round trips to work (~150 miles), through neighborhood, boulevard and interstate conditions with no problems. Engine and ATX are behaving perfectly.

To summarize, the following was accomplished:

1. IAC replaced $125 (no luck)
2. PCV replaced $15 (no luck)
3. TPS replaced $65 (bingo!)

I've got no regrets changing the first two parts. With a car this old, it'll help future troubleshooting to know these parts are new. Thanks for the help, guys - another visit to the stealership avoided! Let's just hope this fix lasts...

Still looking forward to NJC's report from the dealership.

Dan:

Good call. I should've communicated from the beginning that there was no CEL throughout any of this mess.

 

[NJCSVT]

sorry, it took so long on the update, the dealer had my car for a week and couldn't replicate the symptoms...of course the day after i took it home it acted up again.

today i cleaned the IAC, the action of the slide was a little sticky before cleaning, afterwards it moved smoothly. my commute to work today was better, RPM would occasionally spike to 1250 instead of 2500 or 4000 like it was before. if it this seems to cure the problem i'll just replace the IAC, Autozone quoted them at $40. If it starts acting up again i'll try the TPS. Autozone had them for $20 or so.

 

[Dyoel182]

Those prices dont look right. The IAC is usually a $80-90 part and the TPS is more like $40.