Northstar idle RPM after cold start
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Cadillac Seville / Cadillac Eldorado Forum Discussion, Northstar idle RPM after cold start in Past Cadillac Vehicle Discussion; Hi, what would be the correct idle RPM just after cold start, say in -15'C (5'F). My 1997 STS starts ...
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    JHowdy is offline Cadillac Owners Member
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    Northstar idle RPM after cold start

    Hi, what would be the correct idle RPM just after cold start, say in -15'C (5'F). My 1997 STS starts just fine but then runs erratic in cold for a minute or so. This happens when the temperature drops near 0'C and below. I don't have a garage. When this happens I have to keep my foot on the gas pedal for awhile to prevent it to die. This morning just after starting the RPM was over 1000 for a moment, then dropped immediately to 500 and under and I had to help with my foot on the pedal.

    I have read about the possible HG failure symptoms, I do loose some coolant also, very slowly, but suspect it to leak somewhere in the engine compartment. I can feel coolant smell sometimes when driving and the car swings sideways or when turning or braking rapidly. Nevertheless, I'd like to know if this kind of poor running after cold start could be caused by something else, for instance the IAC-valve? Thank you.

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    Submariner409's Avatar
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    Re: Northstar idle RPM after cold start

    In a '97 a poor cold fast idle sequence (~1200 for 30 seconds, 900 for a minute, then 650) could be due to anything - sticky injectors, coolant in a cylinder, faulty spark plug cable(s), coil(s), ISC/IAC, Throttle Position Sensor, dirty TB, PCV restriction or vacuum leak, dirty MAF, fouled air filter. (The idle speed sequence is set by the PCM/ECM - something is preventing the engine from following directions............)

    Any trouble codes set ? Maybe a 20 oz. jug of Chevron TECHRON with a fill-up of a Top Tier gasoline (Google it) would help the fuel system/injectors. The other maintenance is at your leisure, and it's all covered in here, Deville, Northstar, and Cadillac Tech Tips.

    Cylinder block exhaust gas test - head gasket go-no go test. http://www.sjdiscounttools.com/lis75500.html

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    Re: Northstar idle RPM after cold start

    When was the TB last cleaned?

    If you smell coolant, you have a leak. If you smell it while driving, it may be the heater core.

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    JHowdy is offline Cadillac Owners Member
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    Re: Northstar idle RPM after cold start

    OK, there are lots of possible causes and it certainly has a poor cold fast idle sequence. Thank you Submariner.

    I got only these two trouble codes and the explanations are stated here as I found them using google.

    PCM P0603 (History) - Internal Control Module Keep Alive Memory (KAM) Error ? This sounds pretty bad. My car battery should be ok, it was replaced half a year ago and shows a green indicator eye and the engine cranks normally. The DIC shows that the charging voltage is between 13...14V when I'm driving. May be a bit less than 13V when idling.

    IRC B1740 (History) - Driver Seat Front Down Switch CKT Malfunction ?

    I bought this STS last August. Sorry to say I didn't know that the TB should be cleaned periodically, until the cold season started, the troubles began and it was too cold to do it in my parking lot. I don't know when it has been done - if it ever has been done. But I'll have it done in the next maintenance. I'll also ask them what they can do to detect a possible HG failure.

    The PCV valve and air filter have been changed right after I bought the car. The spark plugs, coils and spark plug cables were changed one month ago. That helped the idling between outside temperatures +5...+10'C but the cold idling troubles started again when the outside temp got colder.

    I have ordered a new FPR and will change it as soon as I get it, it seems to have a vacuum leak causing occasional bad warm starts. But that may be another issue and may have nothing to do with this problem.

    ----------

    Oh, Submariner, you mentioned "Idle Speed Control". Did you mean the Idle Air Control valve (IAC) or is there a real Idle Speed Control Motor (ISCM) somewhere? If I google for "1997 cadillac Idle Speed Control Motor" I get links to the IAC only. Confused...

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    Re: Northstar idle RPM after cold start

    I don't think you have any HG problems.

    TB should be cleaned once a year. It's easy to do and I believe there is a tutorial in the Tech Tips section if you want to do it yourself. That may be your entire problem.

    If your FPR is leaking fuel from the nipple after you pull the vacuum hose, it needs top be replaced and could be contributing to the idle problem and definitely will cause hot start problems.

    Yes, when Sub mentioned "Idle Speed Control" he meant the IAC valve.

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    Re: Northstar idle RPM after cold start

    Clarified in the post. Some do have an ISC setup; not sure of the model year breakpoint.

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    '96+ use an IAC valve.

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    Re: Northstar idle RPM after cold start

    Thank you all for your input! I did try to find some ready answers but didn't, and then decided to ask.

    That IAC/ISC thing has been troubling me for some time now, glad that finally I got the answer to that one also. Mine definitively has the IAC, I've found it already but could not spot the (non existing) ISC .

    I found the TB cleaning procedure from this forum about two months ago, it seems simple enough to do it yourself, but as I said it's now a bit too cold to do it outside. The whole cold idle trouble began a bit later.

    My FPR is not leaking much fuel, none visible, but I got the fuel odour to my fingers from the end of the vacuum nipple and suspect it leaking a little and thus needing to be replaced. I've already ordered the FPR, it should arrive any day now. PLUS an OEM SS fuel rail to replace the original nylon rail. I'll probably replace the FPR myself but leave the fuel rail replacement to professionals.

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    Re: Northstar idle RPM after cold start

    The fuel rail might actually still be an active recall - worth asking a dealer if your VIN is under it. Not bad for a car pushing 17 years old (of course the side effect of "spontaneously catches fire" may have something to do with it...)

    Edit: I see the "Finland" - sorry, apparently only nylon degrades in the US (... yeah, right - not even Canada got the recall) but good on you for converting it - gasoline fires are no fun.

    It's worth checking to see if the fuel smell is coming from a cracked nylon injector-injector hose, since if the FPR is really dry that may not be it.

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    JHowdy is offline Cadillac Owners Member
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    Re: Northstar idle RPM after cold start

    Yep, Finland, I'll have to pay for the fun myself. I'm almost certain that the fuel smell came to my finger tip when rubbing the metal vacuum nipple of the FPR, when checking for any signs of gasoline there.

    This morning -11'C, right after start 1800RPM, then dropping to 500 very rapidly, I press the gas pedal, jumping instantly to 2000RPM, then dropping to 500 and nearly dying, and so on. I had to do this 4 or 5 times until the engine started running somewhat steadily, 800-1000RPM. I checked the codes again and got only PCM P0300 - Engine Misfire Detected (Current). But that code must be a consequence of the problem rather than the problem itself.

    The RPM jumping to 2000RPM with just a slight press on the gas pedal surely would indicate problems in the TB and/or IAC action? I'll have it cleaned and we'll see.

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    Re: Northstar idle RPM after cold start

    This sounds more and more like a TPS - Throttle Position Sensor - problem. The electrical sensor attached to the end of the throttle blade shaft.

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    JHowdy is offline Cadillac Owners Member
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    Re: Northstar idle RPM after cold start

    Shouldn't I get a trouble code if the TPS is faulty?

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    "Should", yes.

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    Re: Northstar idle RPM after cold start

    I would think - it is a monitored function, but stranger things have happened with these engines. Discount the other - air leaks, vacuum leaks, dirty TB/idle air passages - first.

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    JHowdy is offline Cadillac Owners Member
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    Re: Northstar idle RPM after cold start

    Okay

    (oh what a stupid auto correction, wouldn't let me type "OK")

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