Rough Idle, Lack of Power, etc
09-23-2003, 10:41 PM
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Rough Idle, Lack of Power, etc My car's been running poorly for a little while now, and I'm running out of ideas as to what is causing it....
She idles rough..there's a very noticeable vibration while driving until you reach 70mph, then it's not as noticeable. She is lacking the pep and pickup she used to have and the gas mileage has also decreased. AutoTap'd the car...not throwing any codes. She had a bunch of misfires (not in any particular cylinder)...changed the plugs, almost all the misfires are gone. She's getting a little knock retard here and there, not a lot. One my friend's said it looks like normal for when torque management is kicking in. Everything else that we've logged with Autotap is within normal range. (Engine coolant temp is high, 200+, but she's still got a stock thermo.)
The even stranger part is some days the rough idle, vibration, etc is worse than others..and it doesn't seem to depend on the weather. There were two days last week where it completely disappeared and was running fine for a small portion of the day.
Someone suggested a bent pushrod...but wouldn't the symptoms from that be there 100% of the time? (She has hit the rev limiter a few times)...
Someone else was thinking the vibration was from the drivetrain...but would that cause her to idle real rough too? (I don't see how..but I might be wrong in my thinking...)
The alignment and wheel balance have been checked so that aspect of it wouldn't be causing the vibration while driving.
Other thoughts from people were gas. She almost always gets Shell 93 gas...but on the few occasions I've put Exxon in it hasn't affected anything.
A dirty IAC was suggested. At idle in park or gear, IAC's are in the 50's or 60's. From what I've read on here that close to normal. Could the IAC still be reading normal through Autotap and be affecting it running?
Another suggestion was to check the O2's..make sure they're working ok. Is there a range that the O2's should be in (at idle, etc)? When she was in park, the O2 readings did change as I pressed on the gas.
Any ideas where to look next?
She's a 2002 A4 with just over 31,000 miles..regular oil changes...mods are TSP lid, K&N filter, electric cutout, FRA, and EBC Brakes.
Also, she does seem to run a little better (smoother..more pep) when I've closed the cutout...
Thanks for any help or suggestions...
-Kristen
-2002 WS6 A4
She idles rough..there's a very noticeable vibration while driving until you reach 70mph, then it's not as noticeable. She is lacking the pep and pickup she used to have and the gas mileage has also decreased. AutoTap'd the car...not throwing any codes. She had a bunch of misfires (not in any particular cylinder)...changed the plugs, almost all the misfires are gone. She's getting a little knock retard here and there, not a lot. One my friend's said it looks like normal for when torque management is kicking in. Everything else that we've logged with Autotap is within normal range. (Engine coolant temp is high, 200+, but she's still got a stock thermo.)
The even stranger part is some days the rough idle, vibration, etc is worse than others..and it doesn't seem to depend on the weather. There were two days last week where it completely disappeared and was running fine for a small portion of the day.
Someone suggested a bent pushrod...but wouldn't the symptoms from that be there 100% of the time? (She has hit the rev limiter a few times)...
Someone else was thinking the vibration was from the drivetrain...but would that cause her to idle real rough too? (I don't see how..but I might be wrong in my thinking...)
The alignment and wheel balance have been checked so that aspect of it wouldn't be causing the vibration while driving.
Other thoughts from people were gas. She almost always gets Shell 93 gas...but on the few occasions I've put Exxon in it hasn't affected anything.
A dirty IAC was suggested. At idle in park or gear, IAC's are in the 50's or 60's. From what I've read on here that close to normal. Could the IAC still be reading normal through Autotap and be affecting it running?
Another suggestion was to check the O2's..make sure they're working ok. Is there a range that the O2's should be in (at idle, etc)? When she was in park, the O2 readings did change as I pressed on the gas.
Any ideas where to look next?
She's a 2002 A4 with just over 31,000 miles..regular oil changes...mods are TSP lid, K&N filter, electric cutout, FRA, and EBC Brakes.
Also, she does seem to run a little better (smoother..more pep) when I've closed the cutout...
Thanks for any help or suggestions...
-Kristen
-2002 WS6 A4
09-23-2003, 11:51 PM
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Re: Rough Idle, Lack of Power, etc When you say "a little knock retard"..how much is a little? Beware, 4 degrees is a LOT.
Double check everything. Especially your plugs. Try some TR6's gapped at 50 thous, especially considering you still run the stock thermo.
Make sure the TB is flat against the intake mani.
Make sure the plug wires are on and click when installed.
Check your ground wires. At drivers fender, passender fender and firewall.
When you take off the oil fill cap... and motor is idling... you dont see any oil puffs coming out...do you? (hope not)
Good luck
Double check everything. Especially your plugs. Try some TR6's gapped at 50 thous, especially considering you still run the stock thermo.
Make sure the TB is flat against the intake mani.
Make sure the plug wires are on and click when installed.
Check your ground wires. At drivers fender, passender fender and firewall.
When you take off the oil fill cap... and motor is idling... you dont see any oil puffs coming out...do you? (hope not)
Good luck
09-24-2003, 07:40 AM
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Re: Rough Idle, Lack of Power, etc How is your gas mileage? - you could have a bad 02 sensor.
your o2 readings should be between 880-930 at wide open throttle.
Routein maintenence stuff like the fuel filter, air cleaner,... would be a good place to start.
The cutout may be messing up the computer a little when you first open it, you would have to drive around for 50-100 miles before the computer learns to adjust fully; but you should not see a significant power loss immediately after opening it.
your o2 readings should be between 880-930 at wide open throttle.
Routein maintenence stuff like the fuel filter, air cleaner,... would be a good place to start.
The cutout may be messing up the computer a little when you first open it, you would have to drive around for 50-100 miles before the computer learns to adjust fully; but you should not see a significant power loss immediately after opening it.
09-24-2003, 09:45 AM
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Re: Rough Idle, Lack of Power, etc Plug wires are on good..I put in TR55's when I changed them. They're gapped at 55. This had been recommended by several other fbody owners, bad choice of plugs? wrong gap? The exact amount of knock I'll have to check again in the log file when I get a chance. I'll check the ground wires tonight or this weekend. TB is flat against the intake...it hasn't been taken off ever, just from the bellow forward. I'll check about the oil fill cap tonight, that's something I hadn't heard of before. Do I even want to know what that indicates?
I'll try the GM Top Cleaner...can't hurt.
I had been thinking pushrods too...until the problem started not being consistently bad...could it still be pushrods?
Haven't tried the dealer...and really don't want to for this. I suspect that they're going to find nothing wrong. She might be going back to the dealer soon anyway to have them check the tranny, if she does, then I'll have them look into it.
Gas mileage had been averaging about 23 mpg...it's down to 19 or 20 mpg. There wasn't any change in how I drive her..no modifications done. The spark plug change didn't improve the gas mileage any.
K&N filter was cleaned at about 26,000 miles. The MAF was cleaned then too just incase any oil had gotten on it.
I typically run with the cutout open all the time so the computer has had about 20,000 miles to adjust to it. LOL. I noticed she had better power and less vibration when I closed it the other day for a passenger's cell phone call.
Thanks for the suggestions. I'll check them out and go from there.
-Kristen
I'll try the GM Top Cleaner...can't hurt.
I had been thinking pushrods too...until the problem started not being consistently bad...could it still be pushrods?
Haven't tried the dealer...and really don't want to for this. I suspect that they're going to find nothing wrong. She might be going back to the dealer soon anyway to have them check the tranny, if she does, then I'll have them look into it.
Gas mileage had been averaging about 23 mpg...it's down to 19 or 20 mpg. There wasn't any change in how I drive her..no modifications done. The spark plug change didn't improve the gas mileage any.
K&N filter was cleaned at about 26,000 miles. The MAF was cleaned then too just incase any oil had gotten on it.
I typically run with the cutout open all the time so the computer has had about 20,000 miles to adjust to it. LOL. I noticed she had better power and less vibration when I closed it the other day for a passenger's cell phone call.
Thanks for the suggestions. I'll check them out and go from there.
-Kristen
