4.9 fast idle

[EldoGuy]

Hi Guys,

Our '92 4.9 Eldo was in the shop for some routine maintenance.

They also did a fuel injection system flush & clean ( passages

included ) and removed the carbon build up in the throttle body.

Since than, the car drives fine but when I slow down it doesn't go

under 1500 Rpm . . . Only when I "STOP" the revs go down to normal.

Idle learn procedure doesn't solve the problem.

Anny suggestions ? :-)

Thanks !

[Scotty]

Have you disconnected the battery? This was posted a while ago by our local GURU, ignore portions of it that don't apply, but there are sections of this post that DO apply, Mike

************************************************************

The air rate thru the throttle body when the blades are closed establishes the idle speed. As deposits build up around the blades and in the bore the air rate is slowly decreased as the deposits effectively seal up the gap around the blade. If this went unchecked the engine would idle slower and slower and eventually stall. To prevent this the idle speed control continually "sees" the extra gain required to overcome deposits. This gain slowly increases with time and miles as the deposits increase. This gain or offset is what is "learned" and retained for the next ignition cycle. The learned gain is different for neutral idle, in gear idle and AC on idle due to the different loads on the engine. The idle learn can only increase...it cannot decrease. It is not in the programming for it to decrease. So, idle learns will always be a positive addition to the throttle angle required for the proper idle speed control initially upon returning to idle. If the deposits are great then the idle learn offsets will be large. Suppose the learns are very large due to lots of miles and heavy deposits...then the battery is disconnected and the learns are lost and reset to the clean throttle body values.....the car could (and probably would) stall the first few times it was driven when the throttle was released. It would do this until the idle learn values were re-learned or re-established with the dirty throttle body. So.....that is why there is an admonishion in the owners manual and in the service manual to always go thru the idle learn procedure when the battery is disconnected.... It is a safety caveat.

If the throttle body is clean then the idle learns will "learn" nothing as the default values of a battery reset is for a clean throttle body. So...if you clean the throttle body, disconnect the battery. If you don't, the first few times you drive the car the throttle will seem to "hang" open and the engine will idle fast when you first close the throttle. That is because the idle learns retained are accounting for heavy deposits...that aren't there anymore. Simple. No magic. Disconnecting the battery resets them to the clean values. Haven't you seen/read this phenomenon reported about one hundred times on the forum..??..."I cleaned my throttle body now my car idles too fast..." Put two and two together here.

The reason it is in the owners manual and written in that simple language is twofold. It is a (potential) safety issue with possible stalling involved. Not everyone gets their throttle body cleaned each time the battery is disconnected. Owners manauls are written at the 3rd grade level. No one would read all the above explaination of when and when not the idle learn procedure is applicable....so....it just says to do it all the time.

The idle speed control is going to function correctly given a little driving the same whether the idle learn procedure is done or not. Do you suppose the idle learn is done when the car was new at the factory....???....NO. It was just driven as the throttle body was clean and the idle learn default values matched that condition.

The simple answer to your question is that when cleaning the throttle body all that is required is to disconnect the battery. Period. Doing the idle learn is not going to hurt anything. But it is not going to help anything either.

[EldoGuy]

Yes, the battery was disconnect for several minutes.

After connecting the battery again, OBD was reprogrammed and idle learn procedure was done.

[Scotty]

Yes, the battery was disconnect for several minutes.

After connecting the battery again, OBD was reprogrammed and idle learn procedure was done.

Disconnect the battery and DON'T do the idle relearn, let the system do it on its own and see what happens.

[teeric92]

I had the same problem and found out my tps was moved out of range and i didn't get a code for about 2 days after adjustment everything returned to normal.

[EldoGuy]

Hi Scotty,

I followed your advise and disconnected the battery and didn't do the idle learn procedure. ( only reprogram computer as per manual )

I still have the same problemo, when driving it is almost impossible to slow down because it wants to idle to 1500 RPM, once I stop idle goes down to normal . . .

I think something is wrong with my ISC motor ( maybe maximum extension needs to be adjusted ? )

Or maybe it needs a TPS adjustment, but than I need the T-25 "L-shape" Torx wrench <BG>

[Scotty]

Have you looked into the TB to see if the rear of the throttle plate and throat are clean? Its possible that something is hanging your throttle plate open, take a look at it when its closed.

[adallak]

Hi Scotty,

I followed your advise and disconnected the battery and didn't do the idle learn procedure. ( only reprogram computer as per manual )

I still have the same problemo, when driving it is almost impossible to slow down because it wants to idle to 1500 RPM, once I stop idle goes down to normal . . .

I think something is wrong with my ISC motor ( maybe maximum extension needs to be adjusted ? )

Or maybe it needs a TPS adjustment, but than I need the T-25 "L-shape" Torx wrench <BG>

You know what... I saw several similar reports. My car does actually the same thing- as if cruise control is engaged. But does it really concern you? You can slow down whenever you want to by braking. The only thing which may be considered bad is the acceleration when you go down a hill. I usually have to switch to 3, 2 gear to spare the brake pads.

[Scotty]

Hi Scotty, 

I followed your advise and disconnected the battery and didn't do the idle learn procedure. ( only reprogram computer as per manual )

I still have the same problemo, when driving it is almost impossible to slow down because it wants to idle to 1500 RPM, once I stop idle goes down to normal  . . .

I think something is wrong with my ISC motor ( maybe maximum extension needs to be adjusted ? )

Or maybe it needs a TPS adjustment, but than I need the T-25 "L-shape" Torx wrench <BG>

Ok, I misunderstood your first post.

You may need to do these adjustments, assuming that the TB throat and plate are clean.

Minimum Air

Adjust TPS

Adjust ISC

See scans, this is from a 91 4.9 FSM

[Scotty]

Continued

[epricedright]

Hi Scotty, 

I followed your advise and disconnected the battery and didn't do the idle learn procedure. ( only reprogram computer as per manual )

I still have the same problemo, when driving it is almost impossible to slow down because it wants to idle to 1500 RPM, once I stop idle goes down to normal  . . .

I think something is wrong with my ISC motor ( maybe maximum extension needs to be adjusted ? )

Or maybe it needs a TPS adjustment, but than I need the T-25 "L-shape" Torx wrench <BG>

You know what... I saw several similar reports. My car does actually the same thing- as if cruise control is engaged. But does it really concern you? You can slow down whenever you want to by braking. The only thing which may be considered bad is the acceleration when you go down a hill. I usually have to switch to 3, 2 gear to spare the brake pads.

Adallak, if your car is running like that, maybe that ISC motor you put in is defective or adjustment is needed? It didn't act right for me either. That's gotta be terrible for your gas mileage and brakes.

[adallak]

Hi Scotty, 

I followed your advise and disconnected the battery and didn't do the idle learn procedure. ( only reprogram computer as per manual )

I still have the same problemo, when driving it is almost impossible to slow down because it wants to idle to 1500 RPM, once I stop idle goes down to normal  . . .

I think something is wrong with my ISC motor ( maybe maximum extension needs to be adjusted ? )

Or maybe it needs a TPS adjustment, but than I need the T-25 "L-shape" Torx wrench <BG>

You know what... I saw several similar reports. My car does actually the same thing- as if cruise control is engaged. But does it really concern you? You can slow down whenever you want to by braking. The only thing which may be considered bad is the acceleration when you go down a hill. I usually have to switch to 3, 2 gear to spare the brake pads.

Adallak, if your car is running like that, maybe that ISC motor you put in is defective or adjustment is needed? It didn't act right for me either. That's gotta be terrible for your gas mileage and brakes.

Could be the ISC motor, but I am nor so sure of it since the previous one did the same. The only procedure I have not performed has been "minimum air" adjustment. I really did not want to play with TPS since the data was close to the recommended one.

The fuel economy and power are great, and the car runs very well. It is hard on brakes only when I drive down a hill, otherwise I cannot really complain. I change the front brake pads and rotors every 25.000 miles or so. They are not expensive so I do not care much.

[epricedright]

Hi Scotty, 

I followed your advise and disconnected the battery and didn't do the idle learn procedure. ( only reprogram computer as per manual )

I still have the same problemo, when driving it is almost impossible to slow down because it wants to idle to 1500 RPM, once I stop idle goes down to normal  . . .

I think something is wrong with my ISC motor ( maybe maximum extension needs to be adjusted ? )

Or maybe it needs a TPS adjustment, but than I need the T-25 "L-shape" Torx wrench <BG>

I had similiar problems with the "sail-on" and determined my ISC motor needed replacing. After doing all the adjustments that Scotty just recommended, and you still have problems, you may need to look at your ISC motor. Does your ISC make excessive ratcheting noises when you turn the engine off? There is great post here that explains how you can clean up your ISC if you'd like to try that first. If you decide to repair/replace your ISC, here is a handy 1/4 flex spinner that Scotty recommended me to get, that might help you get to those hard to reach torx bolts:

http://www.sears.com/sr/javasr/product.do?...ket+Accessories

Here is that thread on how to clean up an ISC:

http://caddyinfo.ipbhost.com/index.php?showtopic=7605

Here is the thread when I had idle problems and the guys here came to my rescue (reading that again...What a Nightmare!: ):

http://caddyinfo.ipbhost.com/index.php?showtopic=2969&hl=

Be patient with the adjustments and procedures. I know first hand how frustrating it can be...atleast it was for me. Good Luck!

[EldoGuy]

Thank you for all the info ... now I have some " things to do "

ISC motor doesn't make any noise at all, I hope the ISC motor is still okay.

Thanx !!

[wreldo]

First, what codes are displayed on the DIC? I chased the same problem for three days exchanging the ISC motor, and it turn out to be a faulty TPS sensor. I just insisted that it was the ISC when the computer kept telling me I had a intermet. TPS fault. Replaced TPS sensor and wow, cured the out of control high idle.

WR