Strange "rev hang" issue while driving
Thread Starter
Drifting
Joined: Mar 2011
Posts: 1,807
Likes: 331
From: Ocala FL
Strange "rev hang" issue while driving
Got back from a trip to AZ to visit my dad and found out dumb dumb me I had left my gps plugged in and turned on while gone. Result totally dead battery.
Threw the battery on the charger, recharged and started up like a champ. I LOVE me some Optima Red Top.
Figured I was good to go but nope...that's not the case at all.
For the past couple hundred miles I've noticed that after cruising at highway speeds when I press the clutch in and expect the car to drop down to the normal idle of ~800 rpm instead I get a "rev hang" and it won't settle to below 1500 rpm until the car comes to a complete stop and sits for between 2 and 15 seconds.
Seems to happen both with the air conditioning on and off. NO codes in the DIC, no CEL, no cues as to what's going on.
It doesn't seem to do it as bad/noticeably at lower speeds and in stop and go city traffic.
I disconnected the battery and let it sit overnight and same thing is happening still.
I'm stumped. Any suggestions on things to check?
Threw the battery on the charger, recharged and started up like a champ. I LOVE me some Optima Red Top.
Figured I was good to go but nope...that's not the case at all.
For the past couple hundred miles I've noticed that after cruising at highway speeds when I press the clutch in and expect the car to drop down to the normal idle of ~800 rpm instead I get a "rev hang" and it won't settle to below 1500 rpm until the car comes to a complete stop and sits for between 2 and 15 seconds.
Seems to happen both with the air conditioning on and off. NO codes in the DIC, no CEL, no cues as to what's going on.
It doesn't seem to do it as bad/noticeably at lower speeds and in stop and go city traffic.
I disconnected the battery and let it sit overnight and same thing is happening still.
I'm stumped. Any suggestions on things to check?
Safety Car
Joined: Apr 2011
Posts: 4,260
Likes: 429
From: Houston TX
Usually that behavior would be typical of a vacuum leak of some kind. Strange that it only begin occurring after the battery was fully discharged. Hopefully someone will be able to help you figure it out.
Last edited by Black 02; Nov 6, 2015 at 11:47 AM.
Thread Starter
Drifting
Joined: Mar 2011
Posts: 1,807
Likes: 331
From: Ocala FL
I thought that too but have not found any vacuum leaks yet. I didn't get to thoroughly inspect though since I was tied up with work all week. Planning to check more thoroughly this weekend. I was also thinking about cleaning the MAF sensor and checking the throttle body to make sure there is nothing happening there for peace of mind.
Cruising
Joined: May 2018
Posts: 13
Likes: 0
I thought that too but have not found any vacuum leaks yet. I didn't get to thoroughly inspect though since I was tied up with work all week. Planning to check more thoroughly this weekend. I was also thinking about cleaning the MAF sensor and checking the throttle body to make sure there is nothing happening there for peace of mind.
No idea if you'll see this or not but I'm having the exact same symptoms with my 02 Z06. Did you ever figure out what the issue was?
Racer
Joined: Feb 2018
Posts: 313
Likes: 56
From: Long Beach California
Huh, my 01 Z06 does the same thing. Doesn't hang there long like the OP, but it'll be slightly higher than idle RPM, and the second I come to a full stop, it goes to normal idle RPM.
Cruising
Joined: May 2018
Posts: 13
Likes: 0
I private messaged him and here is his response in case google brings anyone else here:
I'm going to check for vacuum leaks and I'll update once I find the issue.
Hi,
Thanks for sending the PM...I did not see that you posted in that thread but I got the email notification for the PM. Yes, I did figure it out. It was a vacuum leak in two places.
There is a hose that goes from the top of the throttle body to the valve cover on the passenger side that had a split in it. I was not going to pay for the OEM shaped hose (it was like $50 I think) and was able to get some other hose that the parts store sold by the foot. I don't remember the internal diameter...I want to say it was approx 3/8 id but I could be wrong.
I also had a split hard vacuum line that ran from the back of the intake manifold over to the passenger fender that is associated with the HVAC. Again, I purchased some vacuum line by the foot and replaced that line.
That seemed to pretty much eliminate the issue. Check ALL the vacuum lines you can. Good luck.
Cheers,
E
Thanks for sending the PM...I did not see that you posted in that thread but I got the email notification for the PM. Yes, I did figure it out. It was a vacuum leak in two places.
There is a hose that goes from the top of the throttle body to the valve cover on the passenger side that had a split in it. I was not going to pay for the OEM shaped hose (it was like $50 I think) and was able to get some other hose that the parts store sold by the foot. I don't remember the internal diameter...I want to say it was approx 3/8 id but I could be wrong.
I also had a split hard vacuum line that ran from the back of the intake manifold over to the passenger fender that is associated with the HVAC. Again, I purchased some vacuum line by the foot and replaced that line.
That seemed to pretty much eliminate the issue. Check ALL the vacuum lines you can. Good luck.
Cheers,
E
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Thread Starter
Drifting
Joined: Mar 2011
Posts: 1,807
Likes: 331
From: Ocala FL
To the others that are curious. It turned out to be a vacuum leak in 2 locations.
1. the hose that goes from the top of the throttle body to the valve cover on the passenger side was split on the underside.
2. the hard vacuum line that runs from the back of the intake manifold to behind the passenger fender that is associated with the HVAC controls.
Once both of those hoses were replaced with new vac lines the extended rev hang went away.
Hopefully that helps anyone else that experiences it.
Cheers,
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