Beating a dead horse (overrev)

[K Thompson]

Hey All:
This problem is wearing me out. 2003 30.l 5 speed stick. Between some gears and coming to a stop the engine is revving from 3000 to 4000 rpm only when the ac is on. I have found the vacc leaks and replaces the hoses, replaced IAC valve and have an vss sensor here to install tomorrow. I have disconnected the battery and the truck will run correctly for about 2 minutes. I drove it all afternoon in stop and go traffic today with the ac on. As soon as it would start to rev, I would flip the AC switch from to off and immediately back on. The idle would immediately drop to 700 and never act up until I started shifting again or rev the engine a little at a stop light and it would start the process all over again.

Any and all help is appreciated!!
Keith`

 

[Eddo Rogue]

There's a thing that keeps the engine at 1500 rpm when clutch is pressed until it goes below 5mph, then it drops to regular idle. Maybe your problem is there. I dont think the IAC valve has anything to do w/ it if your idle is normal other than the rev problem.

 

[dvdswan]

Or the FICV, since it happens with the AC on.

 

[RonD]

+1 ^^^

Emissions requirements have any engine staying above 1,000rpms until vehicle is stopped/under 5MPH
In a manual trans vehicle RPMs should hold at current RPMs when shifting, but only for 5-7 seconds or so, so if you hold the clutch pedal down longer then RPMs should drop to 1,500 or so, if above 5MPH
RPMs should NOT go up

AC compressor coming on should bump up idle by 50-75rpm
Higher coolant temp will also cause an increase in RPMs, so ECT sensor error
Throttle sensor may not be showing "closed throttle" all the time
PCV Valve may be sticking open(high idle)

An OBD2 Bluetooth reader is a good investment if you plan on owning vehicles, under $25
These work on any vehicle sold in the US or Canada since 1996, so not a Ranger or Ford thing, any vehicle
You can then see Live Data from all the sensors, you see what the computer sees

In your case the computer seems to be in control of the system, so not a vacuum leak or other issue thats out of the computers control, which is why there are no "trouble codes"
Computer would set "codes" if RPMs were not in the range it expected
Like these
P0505 Idle Control System Malfunction
P0506 Idle Control System RPM Lower Than Expected
P0507 Idle Control System RPM Higher Than Expected

So the absense of codes, means computer "thinks" everything is working like it should

There may be a software update available for your 2003 3.0l manual trans vehicle
Check with Ford Dealer, give them your VIN and they can look up any Software updates
Usually any update will also say what it fixed, and high idle was a common issue on most updates
Ford can do the update but its not free, so if there is an update ask the price



2001-2011 Rangers use an OSS(output shaft speed) sensor on the transmission, 2WD or 4x4, for speed signal to speedometer and cruise
OSS sensor connects directly(only) to the computer(PCM), computer then calibrates the 32,000ppm OSS signal to the 8,000ppm signal needed by speedometer and cruise
Calibration is done using STOCK tire size and STOCK rear axle ratio, just FYI
So changes to either of these will "throw off" speedometer/odometer, tire size and axle ratio can be changed in the PCM via Forscan software, or Ford can do it

VSS sensors were only for ABS system in those years, just FYI

 

[K Thompson]

Thanks for all your speedy responses. I have something to work with and will report back when I get this little beast behaving correctly!!

BTW what is a FIVC?

 

[dvdswan]

Fast Idle control valve. Different from the IAC.

It will raise the idle when the ac compressor is on and when the steering wheel is at full lock.

 

[K Thompson]

Replaced the OSS sensor today along with the pigtail that plugs into it. It is still not correct. If I am slowing from 30 mph or faster, the engine will drop to about 1500 rpm for about 2 or 3 seconds then as you come to 3 or 4 mph it revs to 3000 rpm then sometimes will drop back to 900 or will stay at 3000 till the accelerator is quickly pressed to the floor and released. Again this is only with the ac on. When the ac is off, it behaves normally. I was wondering if there is possibly a vacuum leak behind the dash ie a line that only has vacuum when the ac is on. Frustrated but not giving up!!!

 

[Eddo Rogue]

Is there any chance its your MAF? Usually when I have rpm rev problems its the MAF needs to be cleaned or replaced.

 

[superj]

Is there a throttle position sensor? Maybe it's not working?

 

[Eddo Rogue]

Pretty sure its has both a MAF (mass air flow) and TPS (throttle position sensor)...and one or both might be dirty/bad.

 

[K Thompson]

Thanks guys. I will check these both now!!

 

[K Thompson]

Solved.

It was a faulty throttle position sensor. I really appreciate all your responses to my woes!!!

 

[CavVet2]

Is there a throttle position sensor? Maybe it's not working?

How can you tell if the tps isn’t working right other than to replace it? That can get expensive just throwing new parts at the problem.

 

[superj]

you can take measurements with a multimeter. tps usually read smooth and linearly when opening and checking resistance on the pics.

 

[CavVet2]

you can take measurements with a multimeter. tps usually read smooth and linearly when opening and checking resistance on the pics.

I replaced the tps and it helped. Now the idle when I push in the clutch with it rolling comes down around 1800-2000 and when I stop it comes in down to the correct idle. Can’t figure out why it stays up while moving with the clutch disengaged but it’s better than it was by a lot.