Idle Problems After Mechanic
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HT4100 4.1, 4.5, 4.9 Discussion, Idle Problems After Mechanic in Cadillac Engine Technical Discussion; Ever since I got my car (93' DeVille) back from the shop a few weeks ago, it has had an ...
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    Enigmaticwraith is offline Cadillac Owners Member
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    Idle Problems After Mechanic

    Ever since I got my car (93' DeVille) back from the shop a few weeks ago, it has had an very high idle. It was in the shop for a smog inspection, and to get some oil leaks fixed. My mechanic said he replaced some engine seals, and tightened some bolts, to stop the oil leaks; he also fixed the coolant leak I had, which was from the water pump seal, so he replaced the water pump as well; he removed and welded the PS pump/belt tensioner bracket back together (it had broken near the bolt); he fixed a leaky injector; and finally he replaced the catalytic converter. He said he tried a lot of other different things while trying to get it to pass smog, until finally he replaced the catalytic converter and it passed, so I'm not sure what else he did before that.

    Anyway, after getting it back, the idle is extremely high, it can coast for a few miles at 40mph easily. I have already tried readjusting the ISC motor (which seems to be working fine [i.e. it retracts and extends when I tell it to in the diagnostic menu]). This is causing extremely low mileage in town (6-7mpg), and I also have to ride the brakes at speeds below 25mph. It still seems to get around 25mpg on the freeway, however I can occasionally feel it accelerate by itself when coasting down hills.

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    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: Idle Problems After Mechanic

    The ISC is still out of adjustment. I think the gap is .060" off the top of my head. You could also try the idle relearn procedure from the owners manual. If the car still sails on the ISC is malfunctioning.

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    dennis93coupe's Avatar
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    Re: Idle Problems After Mechanic

    You might want to disconnect the cruise control cable at the solenoid and that will give you enogh slack to remove the cable at the throttle. Try that to make sure it i sn't your problem. Most likely it is the ISC. Have you pulled codes? Read the sticky at the top of the page, how to pull codes. Write them down, look up the definitions (nobody has them memorized) and post back.

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    Re: Idle Problems After Mechanic

    Do this simple test:

    Use the diagnostics to retract the ISC

    Verify that the isc plunger when fully retracted, does NOT touch the throttle lever. If it still does, screw in until there is a gap.

    Go into ECM DATA and observe the TPS. You want a number between -0.05 and 0.05. <---But ONLY with the ISC not touching the lever!!

    If the number is out of this range, the computer will play with the ISC motor until it gets the number it wants and it doesnt care if makes you idle at 40mph to do so.

    Simply trying to "adjust" the ISC screw will do nothing because regardless of where that ISC screw is, the computer will still move the ISC to get whatever TPS reading it wants to see.

    The ISC adjustments can only be done AFTER the TPS is in range.

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    Enigmaticwraith is offline Cadillac Owners Member
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    Re: Idle Problems After Mechanic

    Okay well there are a few things I've figured out. One, the cruise cable was stopping the throttle lever from resting on the minium air screw. Two, at minium air it idles around 900-1000 rpms. Three, it doesn't have any vacuum leaks as far as I can tell, and I double checked with a gauge and it reads at around 18 inHg. Four, the car will run when it's adjusted down to about 550-600 rpms, however barely. At that range, it seems to pulsate; sounding like it's about to die, then revving itself back up and repeating that. And I may have somehow missed it, but I didn't see any way to read the TPS voltage through the diagnostic menu, so I haven't been able to check that yet.

    Oh, and the only codes are:

    E52 - PCM Memory Reset
    F48 - Refrigerant System Problem

    The first is from replacing the battery recently, and the second is because one of my A/C refrigerant hoses busted.

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    Re: Idle Problems After Mechanic

    Just press OFF to back out of ECM OVERRIDE, where you retract the ISC from. Then go into ECM DATA and it's the first parameter to show up. Min air setting should be @ 550.

    Order of entire procedure:

    Engine temp 160 or greater
    Timing @ 10deg BTDC

    Set minimum air to 550
    Set TPS to +/- 0v
    Set ISC maximum extension to 1.17v

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    Re: Idle Problems After Mechanic

    pulsating typically indicates timing problem

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    Enigmaticwraith is offline Cadillac Owners Member
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    Re: Idle Problems After Mechanic

    pulsating typically indicates timing problem
    Alright, well, I'll check the timing when I get home.
    Just press OFF to back out of ECM OVERRIDE, where you retract the ISC from. Then go into ECM DATA and it's the first parameter to show up. Min air setting should be @ 550.

    I'm really not sure what I'm missing here, but when I press "off" it does nothing, it stays on the same menu with the ECM overrides, and the menu before that is Output Cycling. Also, if I try to set the minimum air all the way down to 550, the engine almost stalls while adjusting, and it won't start-up again afterward.

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    Re: Idle Problems After Mechanic

    To get into PCM data, press LO. E.9.0 will display and at this time you press HI or LO to get your Specific parameter.
    P.0.1 TPS degrees (angle) of throttle opening
    P.0.4 Coolant temp (celsius)
    P.0.8 is engine RPM

    Your coolant temperature reading is in Celsius so you want it above 80 degrees celsius, (normal operating range is between 85-105 degrees celsius)

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    Enigmaticwraith is offline Cadillac Owners Member
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    Re: Idle Problems After Mechanic

    P.0.1 TPS degrees (angle) of throttle opening
    Oh right, I wasn't thinking. I kept looking for the voltage, not degrees. I ended up using a multimeter, as it was easier to look at while making the adjustment anyway.

    Well, I replaced the TPS sensor as the cable clip was broken off and the housing was cracked, then I readjusted the new one to .5 volts, after which I put the ISC motor back on and readjusted the screw to the correct position. Then I preformed the idle learn procedure and checked the timing which was off, so I readjusted that also.

    Now it runs much better and no longer keeps coasting for miles. However there are two things: one, the idle is still unstable and seems to be rough; and two, when I was setting the timing, the timing mark would jump up a few degrees every once and a while.

    I already tried shutting off the injectors one by one to see if they were all firing and experienced an rpm drop on each one. Also, before anyone asks, I was in timing set mode when I set the timing.

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    Re: Idle Problems After Mechanic

    Check the resistance of the injectors - when they get down below 11ohms, they tend to randomly drop in and out of operation. Factory units are well known for coil failure. You wanna see between 12 and 17 ohms.

    I didnt see any mention of an ignition tune up so if that hasnt been done it may be about time. This will greatly improve idle quality.

    I'm not sure about the timing mark, but I can tell you that I experience this also but it smooths out with an increase in RPM. I usually hold it to about 700rpm when checking/adjusting. Dirty/worn distributor contacts can affect how quickly the arc jumps from the rotor, affecting the moment that the timing light reads the spark. A less than perfect spark plug can do the same...

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    Re: Idle Problems After Mechanic

    Quote Originally Posted by Enigmaticwraith View Post
    my car (93' DeVille) It was in the shop for a smog inspection, and to get some oil leaks fixed. he fixed a leaky injector; and finally he replaced the catalytic converter. He said he tried a lot of other different things while trying to get it to pass smog, until finally he replaced the catalytic converter and it passed, so I'm not sure what else he did before that.
    Did you happen to get the smog test result paper back? I took mine in recently also. It passed after having to abort the test first attempt, second time it passed with low numbers on most everything except NOx. The state has lowered passing numbers on NOx to the point it's going to be hard to pass some day.

    Quote Originally Posted by Enigmaticwraith View Post
    Anyway, after getting it back, the idle is extremely high, it can coast for a few miles at 40mph easily. I have already tried readjusting the ISC motor (which seems to be working fine [i.e. it retracts and extends when I tell it to in the diagnostic menu]). This is causing extremely low mileage in town (6-7mpg), and I also have to ride the brakes at speeds below 25mph. It still seems to get around 25mpg on the freeway, however I can occasionally feel it accelerate by itself when coasting down hills.
    Cap and rotor should help alot if you haven't done so yet. It helped mine, had a slight quiver before I changed those. How many miles does it have on it since plugs, wires, cap and rotor? How many miles on the odometer?

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    Enigmaticwraith is offline Cadillac Owners Member
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    Re: Idle Problems After Mechanic

    Check the resistance of the injectors - when they get down below 11ohms, they tend to randomly drop in and out of operation. Factory units are well known for coil failure. You wanna see between 12 and 17 ohms.
    I tested them all (much more of a pain than I anticipated), and they all tested around 16Ω.

    Did you happen to get the smog test result paper back? I took mine in recently also. It passed after having to abort the test first attempt, second time it passed with low numbers on most everything except NOx. The state has lowered passing numbers on NOx to the point it's going to be hard to pass some day.
    I didn't get the paper back, but I may be able to get a copy from my mechanic. Although, I do know it was becuase of high NOx levels that it wasn't passing.

    Cap and rotor should help alot if you haven't done so yet. It helped mine, had a slight quiver before I changed those. How many miles does it have on it since plugs, wires, cap and rotor? How many miles on the odometer?
    The cap and rotor were replaced about 19,000 miles ago, and I replaced the wires and plugs shortly after that, as there was a wire that had been melted by, and was to arcing to, the exhaust pipe. The odometer is currently at 253,000 miles, however the engine was replaced at around 216,000.

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    Re: Idle Problems After Mechanic

    Quote Originally Posted by Enigmaticwraith View Post
    I tested them all (much more of a pain than I anticipated), and they all tested around 16Ω. I didn't get the paper back, but I may be able to get a copy from my mechanic. Although, I do know it was becuase of high NOx levels that it wasn't passing. The cap and rotor were replaced about 19,000 miles ago, and I replaced the wires and plugs shortly after that, as there was a wire that had been melted by, and was to arcing to, the exhaust pipe. The odometer is currently at 253,000 miles, however the engine was replaced at around 216,000.
    OK, thanks for posting back. I've got 121,000 on my clock. Have original cat, o2 sensor, injectors, EGR, fuel pump, sensors. I may have to do the cat in a couple years. They went from 1402 ppm @15 mph dyno in 2000, down to 481 ppm @15 mph for 2011 on the NOx levels. Politics, they're trying to force my baby off the road.

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    Re: Idle Problems After Mechanic

    I forgot to mention that it's much easier to ohm out the injectors at the harness connector.

    If you have the OEM copper core plugs, they may be close to the end of their life. Re-gapping them could help since it gets wider over time (stock 0.060")

    You can also inspect the distributor cap terminals for wear and check the center rotor contact for debris.

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