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98 Cirrus high idle when engine fully warm

Discussion in '1995-2017 FWD Sedans, Coupes' started by lorenz1, Jan 16, 2020.

  1. lorenz1

    lorenz1 New Member

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    Hi everyone. I recently replaced my spark plugs on my 98 Cirrus v6 and had to take apart the intake manifold to get to the rear plugs. I used a new gasket when I reinstalled the manifold, but now it idles at 1100rpm when the engine is fully warm. It also only happens in neutral or park, if it's in drive or reverse it will idle normally... I disconnected the throttle positon sensor and the rpms surged and then returned to 1100rpm, so it will idle at the same high rpm with or without the sensor connected. I'm a little perplexed... It only happens when it's fully warmed up and the tps connected or disconnected doesn't seem to make a difference. I tested the connector, it's getting around 4.9 volts, I also tested the actually sensor and it has resistance and the resistance changes when I move the throttle, so I'm leaning towards it being a vaccum leak?
     
  2. ImperialCrown

    ImperialCrown Moderator
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    Welcome to Allpar. A vacuum leak will cause a fast idle on these. Try a spray bottle of water to locate the leak?
     
    Bob Lincoln and lorenz1 like this.
  3. AllanC

    AllanC Well-Known Member

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    In addition to the suggestion by contributor ImperialCrown to use spray water to check for vacuum leaks, inspect all of the ports which have vacuum connections. Make sure all are attached properly and there are no cracks or leaks in the lines. See attached image.

    V6 Intake Manifold Vacuum Ports.gif

    Considering the age of the vehicle, it is possible lines and / or connections have become brittle due to heat and have developed a crack or lost elasticity and no longer seal properly on the attachment port.
     
    lorenz1 likes this.
  4. lorenz1

    lorenz1 New Member

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    Thank you for the info. It is possible that the egr valve is leaking as I did reuse the old gasket (didn't have a new one on hand). I also noticed today that if I put the fan on the highest setting, and put it to blow just on the windshield, the idle will go down to normal when in park and will actually hold for a little bit after turning the fan off...

    I will check with some water when possible (it's fairly cold here) and will report back
     
  5. AllanC

    AllanC Well-Known Member

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    The HVAC climate control uses electric actuators to move doors in the system. No vacuum motors used. So that rules out a possible vacuum leak in the HVAC causing increased idle speed.

    This seems rather bizarre that altering the HVAC blower fans speed and / or system mode setting affects engine idle. Try this test. With engine idling move the mode selector to DEFROST / windshield but with a low fan speed. Does engine idle change?

    Another test. Set mode to HEAT / floor and then increase fan speed from lowest to highest setting. Does engine idle change?
     
  6. ImperialCrown

    ImperialCrown Moderator
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    Defrost will engage the A/C compressor (above about 40℉ (4℃) for dehumidification.
    Perhaps the compressor is loading the engine and pulling down RPM?
     
    dana44 likes this.
  7. lorenz1

    lorenz1 New Member

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    I will give this a try whenever I go out next and report back

    Could be but the temperature has been around -5 to -10 Celsius the last few days


    Another funny thing happened... I gave a good solid 4 or 5 pumps on the brake pedal and the check engine light popped up, this time with a p1294 for target idle speed, which left me perplexed. Needless to say it is possible that it's a vacuum problem, but it's just very odd. Currently it's been too cold to test for vacuum leaks and i'm in no rush as I barely drive the car and it runs fine otherwise (it's a beater that i'm hoping to stretch for a few more months)
     
  8. AllanC

    AllanC Well-Known Member

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    Pumping the brake pedal repeatedly depletes vacuum in the power brake booster. The vacuum booster is replenished by a direct connection to the intake manifold. Code P1294 indicates as mentioned the engine does not attain expected idle speed expected, either high or low. One of the criteria for setting code P1294 is vacuum leaks.

    Your vacuum leak could be caused by a leak in the connections or hose between the manifold and the brake booster. Inspect the brake booster check valve mounted at the booster housing. It is also possible that the valve located on the push rod that connects the booster actuator arm to the brake pedal is leaking.
     
  9. lorenz1

    lorenz1 New Member

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    Could be. I tried the fan setting test you mentioned and on windshield the rpms seem to stabilize even when the fan is off and I just move the position from say feet to windshield... it doesn't stabilize all the time, so it's random. On feet nothing happens, doesn't matter fan speed setting. As mentioned previously when it gets warmer outside I may poke around and have a look but it seems like the leak could be coming from a bunch of different places... since I rarely drive the car and it's a temporary beater I am not very concerned at this point. I appreciate all the help and info and if I ever end up finding the leak and fixing it i'll report back.

    Cheers
     
  10. ImperialCrown

    ImperialCrown Moderator
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    I still think that a vacuum leak was introduced from the upper manifold/EGR tube removal to service the spark plugs. Perhaps a gasket has slipped out of position or something got pinched between the manifolds?
    Why would a 2nd problem appear when it is likely related to the original work that was done?
    The factory plenum gasket is generally reusable as long as it isn't damaged.
     
  11. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    Small crack induced in vacuum hose or rigid tubing when servicing the car, and it flexes, depending on whether it's in gear, thus opening the crack at times.
     
  12. lorenz1

    lorenz1 New Member

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    I'm also leaning on it having to do with the manifold removal... I did use a new gasket for the intake, but it should be noted that one of the bolt heads is likely stripped as the bolt was never fully in (was stick out slightly) even before removing the manifold (never had any issues prior, so I didn't even consider the stripped head being a problem)

    As mentioned whenever the weather warms up I will take a closer look as very shortly the car will be sitting for over a month so i'm not overly concerned. I appreciate all the help though
     
  13. ImperialCrown

    ImperialCrown Moderator
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    I believe that there are 2, possibly 3 different intake plenum bolt lengths. This has to be watched carefully upon reassembly.
    My paper EGR gasket fell out where the pipe meets the flange. I didn't notice at first, but it was a vacuum leak. I found the gasket laying on top of the bellhousing. You may hear a hiss. Spraying water on it will change the hiss and the idle speed.

    P1294 is the vacuum leak (target idle) code. The IAC motor is fully closed, but the idle is still too high. The IAC is essentially a PCM-controlled, adjustable 'vacuum leak' that bypasses the throttle valve to control decel/idle air.

    [​IMG]
     
  14. lorenz1

    lorenz1 New Member

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    Yep I think it is the egr pipe gasket... sprayed some carb cleaner on it and the egine rpms dropped significantly. I will change the gasket and report back
     
  15. lorenz1

    lorenz1 New Member

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    I verified a little later in the day by wrapping a cloth around the egr tube and creating a seal with my hand and the rpms dropped, I should have the gasket changed by tomorrow and will report back
     
  16. ImperialCrown

    ImperialCrown Moderator
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    Good diagnosing!
     
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  17. lorenz1

    lorenz1 New Member

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    Thanks. It was indeed the gasket. Put a new one on and the idle went right back to normal. It was also interesting that the top screw is shorter then then the bottom one... for whatever reason when I reinstalled the top screw, it would not tighten but would continue spinning freely when sitting flush on the egr tube pipe... I was a little perplexed because this was the exact same screw I took off the first time when the manifold came off... when I looked at the screw it seemed to have a bulge in the threads near the head (never seen threads like that before)... needless to say I just used a different, longer screw that I had laying around in my parts bin and it did the job, so i'm not sure if it was just the screw that was bad, or some of the threads on the inside of the intake are stripped as well... it doesn't matter at this point since the new screw clearly works, but I realize now that it could have been a combo of bad gasket, and possibly the screw not staying tight
     
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