My 4.9 / 4T60E combination has performed flawlessly for about 2000 miles now....until this past week. I drove it across town and back, and it developed a very high idle / very rich condition. As I suspected, the vacuum line between the throttle body and fuel pressure regulator had split and come off. I replaced the line, and fired it up. Still had both issues.
After some serious head scratching and hooking a vacuum gauge to the car to rule out any further leaks, I decided to pull the fuse to the PCM to reset it. The problem went away and it runs perfectly now.
Here's my question.....I,m using the original chip, so I don't have a check engine light or a way to scan for codes right now. I figure it set and stored a code when the leak developed....but shouldn't the PCM have corrected the high idle by itself once the leak was fixed? Or was "rebooting" the PCM necessary to allow it to relearn the proper idle speed?
I think Santa Claus needs to bring me a nice scan tool for Christmas....
OK...the plot thickens. I drove the car to work today and it started acting up again....idling around 1800 rpm in park. Tried resetting the computer, didn't work this time. On the drive home, I didn't even have to keep my foot on the pedal on the freeway.....until about halfway home, when everything returned to normal. I pulled into my driveway, and she's idling at 650 in drive and about 850 in park.
So....I have no vacuum leaks, and an INTERMITTENT high idle. Where should I start looking? Coolant temp sensor? Any good way to test the CTS without replacing it? ISC motor?
I understand there is an "idle learn procedure" on the 4.9. I've never done it, but have been driving the car for a year now with no idle issues until just recently.
Any ideas?? +'s handed out liberally for all with ideas.
Nov 8th, 2007
Posts: 2126 From: Coeur d'Alene, Idaho Registered: Jun 2002