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-   -   Erratic Idle 99 D1 (https://discoweb.org/showthread.php?t=96388)

colvere 01-06-2018 04:53 PM

Erratic Idle 99 D1
 
Idle on my 99 D1 SD seems to be erratic. I have cleaned MAF, Replaced/cleaned vacuum lines, Replaced Stepper/Idle air, and replaced fuel pump relay. Sometimes idles high like 1500 rpm then 400 rpm or normal 650 rpm. When I put the new stepper it raced to 2000 rpm so shut off and restarted and it went to 1500. repeat and dropped to 1000 then last time normal 650. I assumed it was the stepper just adjusting to its new home.

discostew 01-06-2018 09:47 PM

Re: Erratic Idle 99 D1
 
When you change certain things on these trucks you have to reset the closed throttle position and reset the adaptions. it kind of sounds like you have something like that going on.

colvere 01-07-2018 01:07 PM

Re: Erratic Idle 99 D1
 
so adaptive value reset. Can it be done with any specific odbII device?

discostew 01-07-2018 02:16 PM

Re: Erratic Idle 99 D1
 
Closed throttle position learn might not get done with the adaptions reset. It's it's own little thing. As far as what scanner I really don't know what one does what. I use a T4 when I can keep it working. It gets harder every year.

You have any codes with this thing? Do you have advanced evaps?

D Chapman 01-08-2018 09:44 AM

Re: Erratic Idle 99 D1
 
Autolodgic and T4 are the only scanners I know of that can reset the adaptive values. I'm sure there are others, but I don't think your Auto Zone scanners will do this.

The idel should reset itself over the course of several run cycles assuming you don't have a bad sensor or a wet ECU.

colvere 01-08-2018 12:45 PM

Re: Erratic Idle 99 D1
 
No advanced evap system, haven't checked/taken it in to have codes checked. Runs great outside of erratic idle. this morning 20 degrees started and idled at 650 as it should last night at 41 degrees it started and idled at 2100 rpm but returned to normal after engine warm up.

D Chapman 01-08-2018 01:01 PM

Re: Erratic Idle 99 D1
 
Quote:

Originally Posted by colvere (Post 1070334)
No advanced evap system, haven't checked/taken it in to have codes checked. Runs great outside of erratic idle. this morning 20 degrees started and idled at 650 as it should last night at 41 degrees it started and idled at 2100 rpm but returned to normal after engine warm up.

Sure sounds like stepper motor. But when you replace them and do not reset the adaptive values it may take a few run cycles to settle in.

May also check the coolant temp switch. It's on the front of the manifold. I doubt it's your problem, but maybe.


Also take a look at the ECU. It's under the black cover on the passengers side inner fender. Remove the ECU and open it up - it's easy. You won't mess anything up by doing so. Look for some corrosion on the ECU board. If it looks good just put it back. If it looks like water has gotten into it or there is a lot of corrosion, it may need to be replaced. If water did in fact get in to the ECU you need to find out why and correct that issue. The 1999 D1's had a longer gasket where the hood meets the fender on that side specifically for this problem.

colvere 01-08-2018 06:00 PM

Re: Erratic Idle 99 D1
 
I live in Idaho so 300+ days of sunshine not a lot of moisture in my high desert area. I will check the ECU and call a few more shops to check to see what they use for diagnostic equipment. I was going to replace the temperature sensor just because it is all linked in the mean time I will drive it and see if it gets better over time. I will report codes and any changes after I replace the next sensor.

colvere 01-11-2018 04:35 PM

Re: Erratic Idle 99 D1
 
I did have a temperature sensor code fail it said it was -40 and it is +40

colvere 01-12-2018 01:41 PM

Re: Erratic Idle 99 D1
 
Reset adaptive values and all is right in the world with my disco. On to u joint replacement and possible head gasket replace. It will be nice to have my favorite vehicle back on the road.


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