C5 acting strange
Thread Starter
Heel & Toe
Joined: Jul 2010
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C5 acting strange
I have a 2002 Z06 that has developed an issue that seems like a miss, but the car throws no codes other than a P0128 which to my knowledge has to do with coolant temp. I have replaced the plugs and double checked the wires to make sure they are all clicked into place. The car idles fine, but when I go to leave when the car is cold in morning it has a hard time, the rpms try to drop and I have to play with the throttle to bring the rpms back up when trying to get the car to actually move in gear. Its almost like an on off switch, you can get the car going and youll feel it stumble and then pick back up under light accelation. It also has this miss type feeling at cruising speed, but under wide open acceleration it seems to run great. Im just a little stumped because it is throwing no codes, and I hate to just start throwing money at it blind. I've been thinking the o2s could be giving me issues, but Im wanting input from you guys on which direction to go. Car runs great at wide open, but gives me issues at first start in the morning, and then at cruising speed and light acceleration. Any help is much appreciated. This issue has been going on since before the plug swap.
Pro
Joined: Dec 2010
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I had the same issue a few weeks ago. No codes either. Then after a while I got a CEL and2 codes for a bad O2 sensor. Those codes could have been caused by a bad plug or wire. No loose plug wires found. I had AC irridium plugs that did not have many miles on them and the wires were removed and checked. I bought both front O2 sensors and installed a set of NGK irridium plugs. Codes have not been back and the car starts quicker and has no more "stumbling" during light acceleration. Full throtle was never a problem. I don't know why it corrected the issues, but it did.
Tech Contributor
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
When the car is COLD (under 150ish deg) and or when your are in WOT mode,,,,, Your O2 sensors are NOT providing data to the PCM. WOT and cold start utilize programmed tables to provide AFR data so the engine runs correctly.
What MODs do you have?? That can affect cold running and WOT performance.
Bill
What MODs do you have?? That can affect cold running and WOT performance.
Bill
Last edited by Bill Curlee; Nov 26, 2012 at 11:49 PM.
Team Owner
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Flooring it makes you run in a open-loop mode hence the O2 et. al. sensor signals are ignored.
O2 sensors are indeed the most common culprits for your symptoms. It can also be a bad signal from your MAFS or a post-MAFS air leak. Check your wiring and intake snorkle.
Last edited by wcsinx; Nov 27, 2012 at 11:04 AM.
Team Owner
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Thread Starter
Heel & Toe
Joined: Jul 2010
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Ive cleaned the MAF and the issue continues, I haven't messed with the grounds. I have no problem spending money on it I just don't want to go into it blind and replace things that wont cure the problem. I was hoping someone else had ran into similar issues before.
Drifting
Joined: Apr 2009
Posts: 1,898
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From: Morrisville PA
Also, just because you cleaned the maf doesn't mean the maf still isn't the issue. Shame you didn't have a 97-00 car, you could just unplug the maf and see how it runs in SD mode. I do not believe you can do this with an 01+ car because the IAT is integrated into the maf and the PCM needs that signal for fueling in SD mode.
When is the last time you replaced plugs? You sure there isnt a hairline crack in one of them? Have you been burning any oil at all? No oil on the plugs right?
When is the last time you replaced plugs? You sure there isnt a hairline crack in one of them? Have you been burning any oil at all? No oil on the plugs right?
Team Owner
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Also, just because you cleaned the maf doesn't mean the maf still isn't the issue. Shame you didn't have a 97-00 car, you could just unplug the maf and see how it runs in SD mode. I do not believe you can do this with an 01+ car because the IAT is integrated into the maf and the PCM needs that signal for fueling in SD mode.
When is the last time you replaced plugs? You sure there isnt a hairline crack in one of them? Have you been burning any oil at all? No oil on the plugs right?
When is the last time you replaced plugs? You sure there isnt a hairline crack in one of them? Have you been burning any oil at all? No oil on the plugs right?
Team Owner
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check all the wiring terminals for smashed pins, corrosion, etc.
Drifting
Joined: Apr 2009
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From: Morrisville PA
I was thinking maybe thermal expansion did something to the bad plug and made it operate properly. Just a shot in the dark. Also, he never said his issue was cured when the car was in closed loop. He just said the car runs great at WOT. Did not indicate if the stumbling completely goes away once the 02's take over in closed loop.
Sounds like a maf or ground issue to me.
Sounds like a maf or ground issue to me.
Team Owner
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Well yeah that's all we have to go on. But that's typically indicative of a disagreement between how much air the engine is actually getting and how much the sensors/computer thinks it's getting. In my experience, that usually narrows it down to an issue with the MAFS, intake, or O2 sensors.
OP, did the problem come on suddenly or gradually? If suddenly, what was the last thing you did to it?
With the engine idling, open the hood and feel all around the intake snorkel north of the MAFS. Make sure everything is buttoned up tight and there are no cracks and/or leaks of any sort in the plumbing.
OP, did the problem come on suddenly or gradually? If suddenly, what was the last thing you did to it?
With the engine idling, open the hood and feel all around the intake snorkel north of the MAFS. Make sure everything is buttoned up tight and there are no cracks and/or leaks of any sort in the plumbing.
Thread Starter
Heel & Toe
Joined: Jul 2010
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The problem seemed to be gradual, and has progressed to doing it everytime I drive it now. Last thing I did to the car was plugs, in an attempt to correct the problem which it didn't. The car has hit a point where its pretty consistent and doesn't seem to be getting any worse.
Team Owner
Joined: Mar 2002
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The problem seemed to be gradual, and has progressed to doing it everytime I drive it now. Last thing I did to the car was plugs, in an attempt to correct the problem which it didn't. The car has hit a point where its pretty consistent and doesn't seem to be getting any worse.
O2s will normally start tossing various codes when they go out.
