HT4100 4.1, 4.5, 4.9 Discussion, 4.9 Will Not Idle Below 2500rpm! in Cadillac Engine Technical Discussion; Yeah, MAP of 103 kpa is typical around sea level (where I am). I usually observe 100-103 in my Caddy.
I replaced the fuel pressure regulator, and that had no effect. The car still idles at 1250-1300 rpm.
For those of you who keep chanting ISC motor, forget it, that's not the problem. If you read my previous posts, you'll see that I replaced and adjusted the ISC motor. Secondly, the ISC motor does not move while the idle surges up and down. If the ISC is not moving, WHAT IS CAUSING THE IDLE SURGE?
For those of you who live by minimum idle air screw molestation, that's a ghetto solution. The minimum idle speed screw does not go out of adjustment all by itself all of a sudden.
WHAT ELSE CAN CAUSE THE IDLE SURGE? That is the $64K question.
If that was the case he would never see the "idle switch closed" LED light up.
He better tell us what happened - we all tried to help and gave him our time. Maybe it was a vacuum leak - maybe he left his PCV valve hose disconnected.
Haha, I've learned this lesson too many times owning 4 older GM cars. I will never again buy non-AC Delco ignition modules, pick up coils, EGR valves, alternators, starters, or anything else that is readily available.
I've been burned too many times by crappy "lifetime warranty" replacement parts that fail less than 3,000 miles later.
The worst offender that I've found are Bosch alternators and starters. I went through 3 alternators in 3,000 miles on my 91 Deville before I sold the car and 2 starters before I finally put a Delco-brand on. The worst part was that two alternators failed mechanically (bearings burned out, snapped my serp. belt), and one failed electrically.
Do you recall if the engine returned to normal idle within a minute or 2 of replacing the ISC or was it necessary to get the idle down to 425-450rpm by manually getting the ISC plunger to retract? I fought w/ my ISC for 3 months before I finally found an article online which specified the 425-450rpm requirement.
Oh yeah, we're all gettin jacked here. Something too simple to admit was overlooked. Where's the humility?
The new ISC did fully retract and extend. The throttle switch also worked. After retracting the ISC through the ECM override, I noticed something peculiar. The throttle cam was not on the min air screw even though the ISC plunger screw was turned in as far in as it would go.
At this point, I removed the ISC plunger screw from the new ISC plunger and compared it to the screw from the old ISC motor. The plunger screw on the new motor was significantly longer than the screw on the old ISC motor. I installed the old ISC plunger screw in the new motor, did the adjustment and idle relearn, and all is now well.