I Give UP! 99 D Won't Idle

[t-bank]

99 D with 318 and 160K miles will not ide fast enough to keep engine running without keeping your foot on the gas. This problem has been on-going for the better part of a year. Problem ocurred only sporadically on cold start-up at first but eventually got to the point where it was constant, at start-up and anytime it was idling. To date, I have replaced all the following component / parts;

Battery
Idle Air Control Valve
Throttle Position Sensor
Cleaned Throttle Body
Both O2 Sensors
PCV Valve
Plugs
Wires
Cap
Rotor
Coolant Sensor

Probably something else that I've forgotten by now. I resorted to drilling out the throttle plate stop screw and running it in enough to keep the throttle plate slightly open. Even then it has died a couple of times and since my 19 year old son is driving it now to college, I finally just pulled off the vacuum hose from the PCV valve. Idles way to high but at least it keeps running. I know that running it like this is gonna cause carbon / sludge problems long term but I'm flat outta ideas. Has never, ever thrown any codes. Dealer has no clue so that is not an option. My next move is to replace the PCM but I hate to part with that much jack just on a guess.

HELP!!!!!!!!!!!!!!!!!

[Tobizzo]

I wish I could help, 98 is doing it too. I was hoping someone had some answers for me also.

[NH_driver]

My '99 has been doing the same thing. Here's a remedy:

Disconnect battery cable for aobut 10 minutes. Engine Control Module (ECM) will lose memory. Reconnect cable and truck should start right up.

Now, turn on everything... headlights, hi-beams, A/C, high blower, rear defrost, hazzards, wipers, etc. and let truck just idle until normal operating temp. This will let the ECM re-learn the load idle. Once up to temp, just shut off and restart. Should run like a charm.

Mine's been doing this for about a year, and this corrects it every time.

Now the WARNING...
If your truck is like mine, this condition will soon erupt in a mayhem of bad symptoms, like intermittent stalling, no-start, no shift, hard shifts, etc.
Get it checked out! ;-)

[t-bank]

Thanks for the tips on resetting the PCM NH Driver. I didn't see your reply to my post until I had already replied to your latest post. My son just took the D back to school yesterday so I won't have a chance to try your quick fix until he's back home for Thanksgiving. I think I'm gonna just replace the PCM though since I'm getting tired of fussing with the thing.

Thanks again.

[BleedDodge]

I wonder what kind of charge it's putting out at idle speed? Could it all be from a weak alternator maybe?

[NH_driver]

No, not alternator... at least not in my case.

I have already determined that when mine did this, it was running really, really rich. I think the injector timing was totally messed. Holding the throttle open only compensated the fuel by allowing more air through the throttle body. Foot off the pedal and there was just too much fuel to idle. Restart and floor the pedal and it would chug and sputter until it cleaned out the cylinders, but if you take foot off the pedal again... well you get the picture.

Disconnecting the battery was the only way I found to clear the condition.

[t-bank]

My son was home with the D a couple of weekends ago and I was able to check out some of the sensors as well as the voltage output from the PCM to the IAC valve. I got nothing to the IAC which leads me to believe the PCM is the root cause of the problem. I've located a company in Jacksonville, FL that will rebuild my old one (promised one day turn around) for approx. $280.00 (www.ecudirect.com). Found a couple of references on the web which seemed to confirm they are legit so I'm going to pick up the car next Monday and send them the PCM. I'll post back with the results.

T-bank

[t-bank]

When I got home today for lunch my newly rebuilt PCM from ECU Direct was sitting on the front stoop. I installed it tonight and just got back in from a test drive. The D runs great and idles like a champ! $279.99 for their R & R service (includes return ground shipping) with a lifetime warranty. I overnighted it to them on Monday and had it back before noon on Wednesday. Great service at a reasonable price, I would definitely recommend these folks to anyone with a PCM problem.
Thanks to anyone who offered their assistance while I battled this one over the past 10 months or so. It was a real pain in the $#%! and I'm certainly glad to finally put it behind me.

T-bank

[wilddingo2]

My 99 D starting having this same problem all of a sudden a few days ago. I took it to the dealer and they replaced the idle control valve, and suggested I get a new battery, and clean the throttle body...but I declined those. It drove great on the way home, but did the same thing 2 days later. I'm glad to see this post. I'll try the resetting of the PCM tonight. And if it doesn't remedy the problem for long, I'll try getting the PCM rebuilt as t-bank did. Thanks a bunch!

[cadillaction]

I have the same issue when fast/cold idle speed is needed. Once you drive her a couple of blocks she's fine.....no codes. I'll try the battery disconnect and get back to you guys.

[rjinmt]

see if you have any change in the engine when you disconnect map sensor / then disconnect mass air flow sensor.