Idle help.......
05-31-2015, 11:06 PM
#1
On The Tree
Thread Starter
Idle help....... So i have this issue going on .....still.....and its to the point i cant even drive the car for the fear of it doing this. I hate it. I am to the point now of maybe thinking its computer related? This is a question i posted on here some time back and i thought i had it figured out but no luck..... "Ok, going to try this again as i cant figure it out for the life of me. I have 1998 Z28 A4 and it has a high idle issue that will not stop. What it has been doing is you start it and after a very short time it will begin to idle up almost instantly and it will go to close to 3000 rpms. The only way i can get it to come back down is either shut it off and let it sit for a long time or a couple times i have unhooked the battery and it will go back down but only for a short time then be right back up again. Well i did more research online and lots of people said it sounds like a vacuum leak. Tonight i did yet more checking of vacuum lines and such. All i could find was one that looked "maybe suspicious" that went to the throttle body. I put a hose clamp on it and started the car. The idle was PERFECT and it sounded really good. I let it sit idleing in the driveway for a bout ten minutes and then shut it off. Went back to it about 5 minutes later and started it and it was perfect again. I thought well maybe i got it. I decided to take it for a drive and drove about ten miles went thru a drive thru for supper and shut it off to eat. Started it back up after about 15 minutes and with in about 10 seconds...BAM....right back up to around 3000 rpm and it stayed there all the way home. When all of this tarted is when i changed out the throttle body for a different one. I have since put my old one back on as well as tried several TPS units as well that i have".
Something that happened recently is the car was running ok so i took it for a drive and washed it. I never washed under the hood or anything only the outside. After i left the car wash the idle went back up high again. No clue if its related or not but seemed ironic.
Something that happened recently is the car was running ok so i took it for a drive and washed it. I never washed under the hood or anything only the outside. After i left the car wash the idle went back up high again. No clue if its related or not but seemed ironic.
06-01-2015, 01:32 AM
#2
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A hard vacuum leak isn't going to come and go simply because you disconnect the battery or let the engine sit for a long time, so you can pretty much rule out a broken hose or cracked line, etc. Intermittent issues like this, that can be cured with battery disconnects or engine restarts, are almost always due to some sort of electronic device or tuning issue.
Have you tried cleaning/replacing the IAC?
Have you seen a P0507 (high idle) DTC yet?
Have you tried data logging when the issue is occurring? If it were me, I'd be looking at IAC counts, TPS percentage/voltage, Long Term Fuel Trims, and commanded idle speed to start.
You might in fact have a vacuum leak, but it would more likely be an "internal" sort of leak (such as the EGR or EVAP system having a failed/stuck/intermittent valve allowing additional air flow.) You may or may not get a DTC for this, depending on the exact issue and how long it occurs in a given drive cycle. It's also possible that the IAC is either sticking open (failed valve) or being commanded open (PCM issue) when it shouldn't be.
Scanning software is really a must when dealing with intermittent driveability issues on an OBDII car such as this.
Have you tried cleaning/replacing the IAC?
Have you seen a P0507 (high idle) DTC yet?
Have you tried data logging when the issue is occurring? If it were me, I'd be looking at IAC counts, TPS percentage/voltage, Long Term Fuel Trims, and commanded idle speed to start.
You might in fact have a vacuum leak, but it would more likely be an "internal" sort of leak (such as the EGR or EVAP system having a failed/stuck/intermittent valve allowing additional air flow.) You may or may not get a DTC for this, depending on the exact issue and how long it occurs in a given drive cycle. It's also possible that the IAC is either sticking open (failed valve) or being commanded open (PCM issue) when it shouldn't be.
Scanning software is really a must when dealing with intermittent driveability issues on an OBDII car such as this.
06-01-2015, 05:58 AM
#3
TECH Veteran
Check your mass airflow sensor and your throttle position sensor
06-01-2015, 06:36 AM
#4
I had alot of related idle issue with my car. I had a shop put in new gaskets on the fast intake and made sure the intake system was all sealed up. Then I cleaned the MAF and made sure those small wires were not broj=ken off. Then I rechecked the spark plug gaps and bought new wires for them. My idle issues were much much better.
I had it when started car it would idle to 2500 rpms stay there, and slowly come down, then when you would let up off the gas it would go to about 2000 rpms. My car is an auto too. I did not think I needed spark wires, well glad I bought them.
I had it when started car it would idle to 2500 rpms stay there, and slowly come down, then when you would let up off the gas it would go to about 2000 rpms. My car is an auto too. I did not think I needed spark wires, well glad I bought them.
06-01-2015, 11:07 PM
#5
On The Tree
Thread Starter
A hard vacuum leak isn't going to come and go simply because you disconnect the battery or let the engine sit for a long time, so you can pretty much rule out a broken hose or cracked line, etc. Intermittent issues like this, that can be cured with battery disconnects or engine restarts, are almost always due to some sort of electronic device or tuning issue.
Have you tried cleaning/replacing the IAC?
Have you seen a P0507 (high idle) DTC yet?
Have you tried data logging when the issue is occurring? If it were me, I'd be looking at IAC counts, TPS percentage/voltage, Long Term Fuel Trims, and commanded idle speed to start.
You might in fact have a vacuum leak, but it would more likely be an "internal" sort of leak (such as the EGR or EVAP system having a failed/stuck/intermittent valve allowing additional air flow.) You may or may not get a DTC for this, depending on the exact issue and how long it occurs in a given drive cycle. It's also possible that the IAC is either sticking open (failed valve) or being commanded open (PCM issue) when it shouldn't be.
Scanning software is really a must when dealing with intermittent driveability issues on an OBDII car such as this.
Have you tried cleaning/replacing the IAC?
Have you seen a P0507 (high idle) DTC yet?
Have you tried data logging when the issue is occurring? If it were me, I'd be looking at IAC counts, TPS percentage/voltage, Long Term Fuel Trims, and commanded idle speed to start.
You might in fact have a vacuum leak, but it would more likely be an "internal" sort of leak (such as the EGR or EVAP system having a failed/stuck/intermittent valve allowing additional air flow.) You may or may not get a DTC for this, depending on the exact issue and how long it occurs in a given drive cycle. It's also possible that the IAC is either sticking open (failed valve) or being commanded open (PCM issue) when it shouldn't be.
Scanning software is really a must when dealing with intermittent driveability issues on an OBDII car such as this.
Thanks for all the advice and help so far.
Andy
06-01-2015, 11:51 PM
#6
TECH Veteran
Have you tried a new throttle position sensor ?