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car stumbles at first when cold?

This is a discussion on car stumbles at first when cold? within the General Help forums, part of the LSx Technical Help Section category; ...

  1. #1
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    car stumbles at first when cold?

    Car just started stumbling when I first pull out of the drive everyday for the first ¼ mile or so.
    When I pull out of drive the car will stumble when I give it gas, like it is not combusting air/fuel. Not sure what it is losing air, spark, or fuel. Idles fine but when I push on the gas it falls on its face for that first quarter mile or so, it does the same when I leave from work to go home. I let the car warm up for about 5 minutes every day it’s kept in the garage so it’s not really that cold.
    Any thoughts.

  2. #2
    Your friendly policeman FinZ28's Avatar
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    Any codes? My car was acting similar recently due to a vacuum leak in my PCV system. Check all your spark plug wires, too. One click on the plug itself, two clicks on the coil pack. Also might want to check your MAF and clean it with CRC MAF cleaner if needed. Along the same lines, check your air filter. When was the last time the fuel filter was changed?
    Last edited by FinZ28; 10-08-2012 at 04:22 PM.
    2001 Chevy Camaro Z28 A4
    SLP cold air intake/lid, SLP smooth bellow, Pacesetter LT's, ORY, Magnaflow exhaust, BMR STB, adjustable Panhard rod, SFC's, LCA's, 1LE sway bars, cross-drilled rotors

  3. #3
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    No codes at all. Fuel filter changed last year with a new fuel pump, the air cleaner just cleaned no help, spark plugs new this summer with MSD wires all attached good, I will check pcv system but doesn’t seem to be leaking and once the car gets a minute down the road its gone. I will pull out of the drive and when I push down on the gas it bogs just for those couple of seconds and it’s gone the rest of the drive. I just want to fix it before its something major. I was leaning toward a bad MAF sensor, which I clean with spray every time I do a filter change. I really have no idea might just start replacing parts starting with the cheap ones. how do I check my MAF?
    Thanks

  4. #4
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    A faulty MAF will generally throw a code. Our car had an off idle stumble when we bought it that was caused by a hacked up MAF -- it had been de-bladed and de-screened, but didn't throw any codes. First rule of our cars is don't mess with the MAF. Easiest test is to swap it out for a known good MAF, or to simply unplug it and go for a ride. Pulling the MAF harness plug will throw codes, but it will also force the PCM into speed density mode and the engine will run and drive. You can then plug the MAF back in and clear the codes with a scan tool. Let us know what you find.

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    Thanks, my MAF has no screen in it. Owner before me removed it, I have had the car for 5 years now but maybe that is causing some problems I will unplugging the MAF tonight for the drive home and see what happens. At least it will eliminate me replacing an expensive part.

  6. #6
    ʢ ൧ ൨ ൩ ൪ ൫ ൬ ൭ ൮Ր Ց Ւ Փ Smittro's Avatar
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    K&N air filter?

    Try cleaning your MAF with some CRC MAF cleaner (only use MAF cleaner) let it air dry reinstall and see if there's a change.

    Also agree with Jeff as a course of action to try.

  7. #7
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    Well last night I unplugged my MAF for the drive home and the stumble was still there, as always just for the first quarter mile or so of traffic. The car does have a K&N air cleaner, but it has had that since before I bought it (5 years plus). It almost seemed like as soon as my temp gauge picked up off the “peg” it stops doing it. I will keep an eye on this. Only a few more weeks to drive it here anyway, but I would love to get it fixed before I put it up and then have to think about it all winter. Thanks for the help with the MAF trouble shooting.

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    Do you have access to a scanner? If so, I would check to see if the engine temp gauge that feeds the PCM (not your dash gauge) is accurate. You want to make sure the engine is running in open loop loop when it is cold. Also, looks like you have a '98 with an EGR. If that is leaking exhaust into your intake when cold that could also account for your stumble. Cleaning the MAF should be considered regular maintenance, especially if you run an oiled cotton gauze air filter - such as your K&N. Oil will stick to the MAF wires causing dirt and debris to then adhere to them. This acts to insulate the wires and throws off the calibration resulting in the MAF misreporting air flow to the PCM.

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    I have an odb code reader but no scanner, I thought about just replacing the temp sensor. I routinely clean my MAF with the special cleaner. I should probably put this in my signature, my 98 has a ls6 intake no egr, lt headers with maganaflow exhaust, 228r cam, slp air lid, 3600 stall, and a 3.73 geared 9” rear-end, running on a Frost mail order tune with no problems till recently. Stall and rear-end might not matter to the problem I’m having. I have cleaned the MAF several times in the last week, and last night disconnected it and it still stumbled. I real appreciate the help with this, hoping I can get it fixed before snow. Thanks again

  10. #10
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    Check your plug wires to see if they all click onto the coils and plugs. One could be loose. Another thing to check is the harness going to your coolant temp sensor in the driver side cylinder head. Could be damaged. And replace your MAF when possible. I had a bogging issue a few months back and it turned out to be a disconnected plug wire and I had no codes.

  11. #11
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    It's probably a dirty/sticking or bad IAC. Unplug the IAC and remove it and clean the plunger on it along with the hole/passage it fits in on the side of the throttle body. I'd also look over the plug and wires for the IAC also.

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    Any updates?

  13. #13
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    Quote Originally Posted by Smittro View Post
    K&N air filter?

    Try cleaning your MAF with some CRC MAF cleaner (only use MAF cleaner) let it air dry reinstall and see if there's a change.

    Also agree with Jeff as a course of action to try.
    Whats the best way to do this? remove the maf and clean it out or do it while still hooked up?should you un hook the sensor too?

  14. #14
    Member SuperSSguy's Avatar
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    Quote Originally Posted by pajeff02 View Post
    Do you have access to a scanner? If so, I would check to see if the engine temp gauge that feeds the PCM (not your dash gauge) is accurate. You want to make sure the engine is running in open loop loop when it is cold. Also, looks like you have a '98 with an EGR. If that is leaking exhaust into your intake when cold that could also account for your stumble. Cleaning the MAF should be considered regular maintenance, especially if you run an oiled cotton gauze air filter - such as your K&N. Oil will stick to the MAF wires causing dirt and debris to then adhere to them. This acts to insulate the wires and throws off the calibration resulting in the MAF misreporting air flow to the PCM.
    Maybe this question should be on a poll But which do you prefer? Oiled A/M filter or paper (dry) air filter? Heard that alot of oiled a/m filters cause the oily maf problem you stated^?

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    Quote Originally Posted by SuperSSguy View Post
    Whats the best way to do this? remove the maf and clean it out or do it while still hooked up?should you un hook the sensor too?

    Disconnect MAF and remove it from engine bay, then clean it out and let air dry.

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    Quote Originally Posted by SuperSSguy View Post
    Maybe this question should be on a poll But which do you prefer? Oiled A/M filter or paper (dry) air filter? Heard that alot of oiled a/m filters cause the oily maf problem you stated^?

    Just the facts: An oiled cotton gauze filter allows more dirt into an engine than a paper filter. Despite the advertising claims of increased horsepower, you'll find alot of info on this topic that basically shows you can make the same power running either a paper or dry nanofiber media filter. My personal preference is the Amsoil Ea Air Filter.

  19. #19
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    ^ Thanks

  20. #20
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    no updates yet working on jeep all weekend getting ready for winter, I will clean my IAC tonight

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