When the car is in park, running at any temp. the idle surges up and down.
I A C motor small part on throttle body ,controls idle mixture when they fail at idle the engine "hunts" for proper air/fuel mixture . when defective it causes o2 sensors and TPS to compete to set an idle thus the up n down effect.. auto wreckers if your broke new from your local parts store....dealer to much 1 plug in two bolts for most applications
SOURCE: 1999 cadillac deville overheating
That sure sounds like a headgasket failure even if the engine recovers at an idle.
It seems you have done the likely suspects already.
If you haven't done it, check coolant overflow tank for exhaust fumes and discolored or oily coolant and engine oil for any cream-colored effect.
Neither of these missing means the headgasket is good but they are sure clues if you see either fouled.
You could also start cold, leave the radiator cap off (if you still have one) and watch for bubbles as the coolant starts to circulate.
If this problem has been coming on gradually, your radiator may be limed too far closed especially if anyone has used tap water in it for years.
If you can reach it, check the radiator to see if the temperature is roughly the same from top to bottom; that will tell you whether the coolant is passing through all of it. You wouldn't have to wait for it to get scorching hot for this.
SOURCE: 1989 cadillac coupe deville radio
BLACK-ground
RED-accessorie
YELLOW-power 12v
PURPLE-left rear
GREEN-right rear
WHITE-left front
GREY-right front
BLUE-REMOTE
and the other blue one is for remote antenna..
SOURCE: codes po174/171 cadillac deville northstar engine
Check for vacuum leaks around the intake. This is the most common cause for these codes.
SOURCE: pcv valve location
Most common location is mounted to the valve cover gasket. It will have a hose coming from it going to your breather pan and connected to the breather element inside the pan where the air filter is.
Greg
SOURCE: 1991 cadillac deville 4.9 fuel trouble
You just need to go through a simple Idle Relearn Process.
The Idle Speed Control motor will cause the accelerator pedal to tap and the car will surge back and forth, actually acting like there is a lack of power during intial startup.
Whenever a battery is changed, went dead or the ECM computer is replaced.
In order to make the engine run normal again, you need to take the car through a relearn process. Otherwise the idle could be very slow or have a 30mph idle.
To enable it to relearn, here's what to do.
1) Disconnect the battery cable for 15 minutes, before hooking it back up.
2) (KOEO) Turn the Key On with Engine Off, just so the electronics are on, but without starting the engine and turn the climate control panel to off.
3) Push the off and warmer buttons on the climate control panel at the same time and hold for up to 5 seconds for the computer to go into diagnostics.
On the fuel panel screen it will display 888 then E52 and then 70.
When it gets to 7.0 shut off the key for 1 minute.
4) Repeat step 3, two more times.
5) Start the engine without pushing on the accelerator pedal and let it run for 18 minutes with the climate control panel off.
6) After 18 minutes put your foot on the brake and shift into drive and wait 1 minute.
7) Then turn on the a/c by pushing the auto button. It needs to be warmer than 60 degrees F so the compressor can engage. Wait 1 more minute.
8) Put the shifter back in park and turn the key off.
9) Wait 1 minute
10) Idle relearn is now complete and the engine should start and run correctly.
Fig. 33: Vacuum circuits - 1984 V8 4.1L engine Calif. (DFI)
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and I'll appreciate your time and consideration if you leave some
testimonial comment. Have a nice weekend and thanks for using FixYa.
Jose.
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it was the EGR vacume selanoid and regulator. a part that is no longer in production.
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