High idle problems
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Intermediate
Joined: Sep 2018
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High idle problems
Hi I'm new to the forum and not exactly sure how this works but I have a c5 base manual with a stage 4 BTR Cam, American racing longtubes, xpipe, corsa extreme mufflers, and an aftermarket intake (don't know the brand off the top of my head). My check engine light is on for the MAP sensor and I'm not sure if this is the problem or not but when I'm driving ill throw the car into neutral to come to a stop and sometimes it will continue to idle at around 2000 rpm and just stay there. not sure if it could be a vacuum leak or the sensor or what but please help! 
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From: Southlake, TX
Welcome tot he forum!
The first place I'd start is fixing what your CEL is telling you... the MAP sensor. Since you have had a bunch of work done to the engine, a vacuum leak is not out of the question. Start by double tightening anything intake related and checking hoses for cracks.
The first place I'd start is fixing what your CEL is telling you... the MAP sensor. Since you have had a bunch of work done to the engine, a vacuum leak is not out of the question. Start by double tightening anything intake related and checking hoses for cracks.
Team Owner
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From: Central PA. - - My AR15 identifies as a muzzleloader
I believe in the Beer Fairy
Sounds to me like you're in the market for a tune. Many of the people that do Tunes do not do a very good job at drivability and idle quality. Horsepower is easy to make, drivability, not so much.
Pro
Joined: Jun 2015
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From: Madison WI
Use the built in code scanner and see with that light is (or let us know what it is if you already know). It is possible your cam is triggering the light because of lower idle vacuum from the cam.
If you haven't had a pro tune done (not just mail order) than you need it, that is a lot of bolt-ons that will not work well with a stock tune. That can cause hanging RPMs, poor idle, and so much more. Also as recommended, look for vacuum leaks, there isn't that much to check and you want to be certain there are none before tuning.
If you haven't had a pro tune done (not just mail order) than you need it, that is a lot of bolt-ons that will not work well with a stock tune. That can cause hanging RPMs, poor idle, and so much more. Also as recommended, look for vacuum leaks, there isn't that much to check and you want to be certain there are none before tuning.
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Thread Starter
Intermediate
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The car has a base tune on it supposably, its been diving fine for the last month and just recently this issue started to happen.
Pro
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From: Madison WI
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Pro
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From: Madison WI
The aftermarket intakes tend to fit VERY close to the cowl & firewall, if the MAP sensor is located there as it is from the factory, it can rub and work itself lose. I had this happen and had to remove the intake and trim the extra plastic around the sensor and use some thread tape to make it fit very snug in the hole it fits into the intake.
Otherwise you have the EVAP (if not deleted) along the drivers side valve cover that is pretty easy to get to. Also the brake booster which isn't as bad to get to that attaches to the back of the intake as well - but idk if I've ever seen that leak.
Then between the MAF and throttle body is the 2 fittings on the throttle body itself on the passenger side that go to the passenger side valve cover and the other either comes from the top of the valley cover (Z06) or the other valve cover.(drivers side, around the back and along the passenger valve cover as well).
I think that is it for possible leaks.
Otherwise you have the EVAP (if not deleted) along the drivers side valve cover that is pretty easy to get to. Also the brake booster which isn't as bad to get to that attaches to the back of the intake as well - but idk if I've ever seen that leak.
Then between the MAF and throttle body is the 2 fittings on the throttle body itself on the passenger side that go to the passenger side valve cover and the other either comes from the top of the valley cover (Z06) or the other valve cover.(drivers side, around the back and along the passenger valve cover as well).
I think that is it for possible leaks.
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From: Cape Coral, Florida
Last edited by C5 Diag; Oct 2, 2018 at 02:58 PM.
Thread Starter
Intermediate
Joined: Sep 2018
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Use the built in code scanner and see with that light is (or let us know what it is if you already know). It is possible your cam is triggering the light because of lower idle vacuum from the cam.
If you haven't had a pro tune done (not just mail order) than you need it, that is a lot of bolt-ons that will not work well with a stock tune. That can cause hanging RPMs, poor idle, and so much more. Also as recommended, look for vacuum leaks, there isn't that much to check and you want to be certain there are none before tuning.
If you haven't had a pro tune done (not just mail order) than you need it, that is a lot of bolt-ons that will not work well with a stock tune. That can cause hanging RPMs, poor idle, and so much more. Also as recommended, look for vacuum leaks, there isn't that much to check and you want to be certain there are none before tuning.
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Joined: Sep 2013
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From: Cape Coral, Florida
Thread Starter
Intermediate
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Ive owned the car for about 8 weeks, Cam was put in a few weeks before I got it, it was also dyno tuned before I got it
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
So you’ve had the car for 8 weeks and now it’s throwing these DTC’s ??...Don’t know what kind of valve overlap and hence vacuum you have with that cam but the MAP DTC (circuit high input) most likely isn’t due to that. Low vacuum = high voltage (more than 4.9 volts)...you can check the voltage with a DVOM but getting to the connector is a challenge.Do you have a vacuum gauge to check how much you have ??...my stock ‘01 runs at a steady 21 inHg at idle and I have no loose teeth...LOL !!...Wouldn’t even want to speculate on your 2 O2 DTC’s without having a tuner check it out...again !!
Last edited by C5 Diag; Oct 2, 2018 at 09:58 PM.
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From: Central PA. - - My AR15 identifies as a muzzleloader
I believe in the Beer Fairy
My car that I just sold had 12 degrees of overlap and over 600 lift, and it idled at 675 about as nice as they can idle. It did take me a fair amount of time to get it there but I did get it.
as the seasons change and air density changes, if your tune is not on it will give you all sorts of problems with the fueling. I think you have something more serious than that but if it's already right at the edge of being wrong, a little air density will put it over the top.
you've got a tough one to solve over the internet, especially with you not having HP tuners or some other method of tuning. I wish you luck finding it but I suspect you're going to need work on the drivability tune which just takes time.
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Joined: Sep 2013
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From: Cape Coral, Florida
I'm always skeptical when I hear someone say base tune. IMO, it is either tuned or it isn't. If it's only partially done, it's not done. That doesn't mean you can't drive it that way but it isn't done.
My car that I just sold had 12 degrees of overlap and over 600 lift, and it idled at 675 about as nice as they can idle. It did take me a fair amount of time to get it there but I did get it.
as the seasons change and air density changes, if your tune is not on it will give you all sorts of problems with the fueling. I think you have something more serious than that but if it's already right at the edge of being wrong, a little air density will put it over the top.
you've got a tough one to solve over the internet, especially with you not having HP tuners or some other method of tuning. I wish you luck finding it but I suspect you're going to need work on the drivability tune which just takes time.
My car that I just sold had 12 degrees of overlap and over 600 lift, and it idled at 675 about as nice as they can idle. It did take me a fair amount of time to get it there but I did get it.
as the seasons change and air density changes, if your tune is not on it will give you all sorts of problems with the fueling. I think you have something more serious than that but if it's already right at the edge of being wrong, a little air density will put it over the top.
you've got a tough one to solve over the internet, especially with you not having HP tuners or some other method of tuning. I wish you luck finding it but I suspect you're going to need work on the drivability tune which just takes time.
Thread Starter
Intermediate
Joined: Sep 2018
Posts: 29
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I'm always skeptical when I hear someone say base tune. IMO, it is either tuned or it isn't. If it's only partially done, it's not done. That doesn't mean you can't drive it that way but it isn't done.
My car that I just sold had 12 degrees of overlap and over 600 lift, and it idled at 675 about as nice as they can idle. It did take me a fair amount of time to get it there but I did get it.
as the seasons change and air density changes, if your tune is not on it will give you all sorts of problems with the fueling. I think you have something more serious than that but if it's already right at the edge of being wrong, a little air density will put it over the top.
you've got a tough one to solve over the internet, especially with you not having HP tuners or some other method of tuning. I wish you luck finding it but I suspect you're going to need work on the drivability tune which just takes time.
My car that I just sold had 12 degrees of overlap and over 600 lift, and it idled at 675 about as nice as they can idle. It did take me a fair amount of time to get it there but I did get it.
as the seasons change and air density changes, if your tune is not on it will give you all sorts of problems with the fueling. I think you have something more serious than that but if it's already right at the edge of being wrong, a little air density will put it over the top.
you've got a tough one to solve over the internet, especially with you not having HP tuners or some other method of tuning. I wish you luck finding it but I suspect you're going to need work on the drivability tune which just takes time.
Pro
Joined: Jun 2015
Posts: 537
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From: Madison WI
Hanging idle or RPMs is almost always from too much air. If everything is sound mechanically (including vacuum) than its the RAF or Base Airflow (whatever you want to call it) - its not something that weather can really affect enough to even notice because the car does have short term and long term idle air trims to compensate for weather and minor changes to incoming airflow.
So my money is on a vacuum leak or something else introducing more air than what the MAF is seeing. If it ran fine for weeks with current tune, its likely not the issue.
I do my own tuning when it comes to idle, part throttle, and cruising - and take it to a pro tuner for WOT (also have them tweak my settings a bit).
So my money is on a vacuum leak or something else introducing more air than what the MAF is seeing. If it ran fine for weeks with current tune, its likely not the issue.
I do my own tuning when it comes to idle, part throttle, and cruising - and take it to a pro tuner for WOT (also have them tweak my settings a bit).