Slow deceleration

[DFlaJax]

'97 LSC with idle problems. Replaced IAC, all codes cleared. Idles fine now around 750, but very slow to decelerate at all speeds. Even at 60, 70 mph when I come off pedal rpms hold steady several seconds, then gradually falls. Dont know where to start looking-IMRC's, tranny issues, vacuum? No luck with forum search, keyword recommendations appreciated.

 

[NoLimit95]

'97 LSC with idle problems. Replaced IAC, all codes cleared. Idles fine now around 750, but very slow to decelerate at all speeds. Even at 60, 70 mph when I come off pedal rpms hold steady several seconds, then gradually falls. Dont know where to start looking-IMRC's, tranny issues, vacuum? No luck with forum search, keyword recommendations appreciated.

Changed the TPS yet?

 

[LaserSVT]

+1 TPS would be my next guess. Also clean the MAF meter.

 

[NoLimit95]

I see you only have 6 posts so just in case, we're talking about the (throttle position sensor) mounted to the throttle body by 2 phillips head screws if I'm not mistaken. The cost for this part will range from $40 to $60 and it's a simple change on your model, unlike the Gen 1's TPS and IAC.

 

[Chadly]

You can test it before you replace it if you have a volt meter. 3 wires, ground, 5V dc constant, and variable. Variable should be less than 1V and gradually go up to ~4.9V at wide open. Need to test it with key on engine off.

 

[DFlaJax]

Thanks guys for the quick replys. Replaced TPS, no change. Was hoping to find original TPS, found mounting bolts stripped so I guess previous owner had been there/done that. Had to remove throttle body to pull TPS, when removing throttle cable found plastic cable guide in 2 pieces at either side of engine mounting bracket, is this normal? Also had to pre-load (?) TPS to install over throttle valve tab. Today will check new TPS voltages, research throttle cable and clean MAF. Got Bank 2 O2 code during test drive, read & reset at parts store, didnt return on trip home. Anxious to get engine running right to move on to pulling tranny pan.

 

[nsjuice]

I wonder if I have the same issue.

But mine vibrates at idle 1k ish even in neutral.

 

[DFlaJax]

Still hanging idle

Initially idles better with IAC unplugged, hanging idle worsens as engine heats up. Cleaned throttle body, no help. Checked again with throttle and cruise cables off, still hanging idle. Should I try with intake air tube off? Does EGR factor in to hanging idle?

 

[XLRVIII]

Also had to pre-load (?) TPS to install over throttle valve tab. .

Sounds like someone turned the "idle stop screw" which is NOT to be adjusted to control idle speed.

Thats probably why you had to "preload" the TPS to get it installed.

There is a procedure for "resetting" idle once someone screws up and twists that screw, but it's ALOT to TYPE.

Basicly,
Unplugg IAC.. then set the idle roughly where you want it via that screw then plug the IAC back in.
Rinse Lather Repeat until you get the desired effects.

with the IAC unplugged you want to lower the idle speed as low as it will go without stalling, your trying to get the throttle plates fully closed into the idle position.

ALSO, someone might have screwd up your throttle body which will also cause a hanging idle.
Many times people will use the "not safe" carb cleaner to clean the TB.
Problem is.. when ford builds the TB they shoot "Clear coat" onto the BACKSIDE on the throttle blades which creates a seal between the TB blades and the bore {not a 100% seal) but...still.

Then someone sprays the wrong cleaner in there, and it removes that clear coat.. THEN you now have more air going AROUND the Throttle plates, and a higher, uncontrollable idle.

Hope this helps.

 

[XLRVIII]

Does EGR factor in to hanging idle??

Nope.. not really

 

[DFlaJax]

Hanging idle

So whats a good gauge on closed throttle plate to bore clearance? When I had it out to replace the TPS, noticed clear daylight nearly completely around throttle plate. If its bad, what donor throttle bodies are good? Checking threads now, thanks XLRVIII for pointing out the possibility of throttle body/idle stop screw problems.

 

[topher5150]

So whats a good gauge on closed throttle plate to bore clearance? When I had it out to replace the TPS, noticed clear daylight nearly completely around throttle plate. If its bad, what donor throttle bodies are good? Checking threads now, thanks XLRVIII for pointing out the possibility of throttle body/idle stop screw problems.

i have a couple or donor throttle bodies

 

[DFlaJax]

Hanging idle

YES! Not there yet, but much better! Adjusted idle stop screw and idle doesnt hang as high or as long as before. Probably moved by prior owner to comp for bad COPs I replaced a while back. Now I'm thinking I need to put a meter on the TPS to see if its in the ballpark. Pulled the IAC connector and disconnected the battery, then ran for about 50 miles total (streets & highways) with no codes, so things are looking up. Thanks again XLRVIII.

 

[XLRVIII]

glad to hear your getting some relief/positive results.

if you had to twist that screw, then you probably will want to revisit the TPS voltage.


With that said, the Mark 8 uses a control system called "coasting fuel shut off".
After a calibrated amount of time (25 seconds) of decelleration the PCM will completely shut off the injectors after certian criteria is met.

if your still having slow decel, then adjusting coasting fuel in the tune will offer some relief.

I changed the "time to enter" coasting fuel from 25 seconds down to 10 and my car decellerates quite aggressively.

Without opening the software and digging all the conditions out, there is another function that is minimum load to enter CFSO.

If you have a vacuum leak OR a bad maf sensor you may not meet the criteria to "enter" CFSO..and the car literally will keep driving itself down the road.. at 40ish MPH..

does this sound familar?

 

[DFlaJax]

Not since I moved the idle speed screw. Still hanging some, but drivable & no codes. Havent touched the MAF, considering new TB. What program do you use for tuning?