Hello, I posted this on another site also so some of you may recognize this.

I have a technical question that I hope someone here can answer. First a little about the car:

It is a 2001 C5. It's got Kooks headers,LG Motorsports G5X3 cam kit, Roll Master double roller timing chain,ASP Under drive pulley kit, 160 degree thermostat, Comp Cams 921 spring kit, Ported oil pump, aftermarket brake calipers/rotors, C6 Exhaust, X-Pipe, high flow cats, custom leather seats, aftermarket rims/tires, aftermarket cowl induction hood, and only 46k on the odometer. Also, its a six speed manual transmission.

Now the problem:

I bought it in Virginia and drove it back to Maine today. About 14 hours in the car so I was really able to get a feel for it. I was told by the PO that it was dyno'd at 400 rwhp and it really feels like it. I've never owned a car like this or driven anything remotely this strong. It's very very torquey and does not want to go slow.

The issue comes when I and coming rolling up to a stop. I'll depress the clutch and shift into first gear (for examle when waiting for a light to turn green). At that point, the tachometer will do one of three things. 1. it may instantly settle out at about 900 RPM and idle fine or; 2. it may settle out at about 2000 rpm and stay there idling (in which case I have to rev the engine to get it to come back down to a 900 rpm idle or; 3. the idle will fluctuate between 400 rpm and 1200 rpm several times (sometimes ending in a stall), until it finally settles out at 900 rpm.

I was told by the PO that it was programmed to have a high idle because the cam would lope so much as to make it stall. Oh, BTW, the problem seems to be exagerrated when the air conditioner is on.

It makes it difficult to drive this car because I'm always worried about it stalling or I'll end up trying to drive away with the RPM starting at 2000. I have driven clutch cars for years and I assure you that it's not the driver

Does anyone have any ideas? This car is in fantastic condition and was well taken care of. It was not beat up.

I also had it hooked up to a code reader and there are no codes showing.

 

Sounds like it's time for you to find a tuner in your area. A good tuner can take care of all the issues you're having with the idle.

 

Do you know who did the original tune? I know of a good tuner (Slowhawk Performance) in Mass but don't know anyone in Maine. A lot of guys drive down to have their cars tuned at Slowhawk from NH and other states. You may also want to get this looked at before the winter fuel arrives.

 

Post in the regional section asking if there are any good tuners near you.

 

Just curious,did the seller provide you with a dyno sheet that would verify the original tuner?

 

Welcome to the forum armycopter.

The hanging idle issue is pretty common, it happens with mine occasionally. It takes some extra effort but I've read that it can be fixed with more careful tuning.

Try the search feature for this forum and you'll see a few posts on this topic. Some of the guys who post in the tuning section on here are pretty well informed and I'm sure will be able to explain whats going on with your tune in more detail.

I hope you enjoy the new ride

B

 

Thanks guys, I'll start looking for a tuner. Hopefully there is one closer than Mass! I just pulled out the MAF sensor and cleaned it with a q-tip and some alcohol. They were a little dirty. Maybe that will help. I haven't driven it yet to find out.

Also, maybe the throttle body is dirty? I read some things about a "catch can" and that all of these cars need one? Anyone know? Seems strange that GM wouldn't put one in if it really needs one. Then again, I guess that wouldn't really surprise me.

Thanks for everyone's input, I really appreciate it!

 

Sounds like a vacuum leak.

 

I agree or unmetered air getting past the MAF. Have you looked carefully at the air-bridge to insure its attached properly. Also look for holes in the PCV valve connection tube from it to the intake. Certainly tuning could be an issue.

 

^^^ Could be a leak or the tune really, but I have had the same issue with unmetered air coming in before.

 

Could be a number of things. I have seen our cam act that way if it isn't programmed right. Takes a bit of work to get a cam like that to behave itself in traffic.

Could also be a vacuum leak as well, either hose or at the intake.

Should be a couple good shops up in that area that can help you out. If you need a list, please let me know and I can direct you over to one.

 

as others have said, a good tuner should be able to take care of it if there isnt a vacuum leak.

 

Wow, thanks for all the great responses! Does anyone know of a thread that can show me how to find a vacuum leak?

I do have an update however. I think I've cured about 90% of the problem. As I stated above, I cleaned the MAF sensors this morning and then performed the idle relearn procedure. Just got back from about 30 miles of driving, including lots of in-town stuff. I drove it with both the air conditioner on and with it off. My problem only surfaced once, right at the beginning of the drive. Other than that it seems to be ok. I'm not 100% convinced yet but at least it's better.

Also, the other thing that I found when I was cleaning the MAF was that the air cleaner box was not put together properly. The PO had "CUT" the airbox so that it fits up against the intake on the cowl induction hood. (doesn't this seem kind of hokey?). The box itself consists of three pieces including the K&N air filter. The filter was in backwards and the box was not sealed properly. I cleaned the filter and put it in correctly. Although there could be air getting in and around where the cowl induction hood meets up with the airbox, at least the airbox itself is no longer leaking. I also made sure the air bridge is all nice and tight.

I am still interested in verifying that there is no vacuum leak if someone could point me in the right direction.

Thanks again! This morning I knew nothing about the corvette's engine... now I know all about the air intake portion, filter, MAF, air-bridge, etc due to all the info I have found on this forum.

 

Do a visual of your throttle plate to see if it has a hole drilled in it. It should NOT, but some tuners drill a hole (used in other LS1 applications).

As said many times before, a good tuner can fix this, as long as no hole is drilled.

 

Thanks, I looked at it this morning and there was no hole drilled in it.

 

Can you post some pics please? I'm not familiar with this setup, and the corvette does not have a cowl induction hood(stock), as the air is taken from underneath.

 

Ok, these pictures are kind of hard to see but here goes...

I do not think this hood is stock. The air is drawn in by the reverse cowl near the windshield. It draws down the length of the hood and dumps into the cut airfilter box.
This part is up near the windshield



This part is down by the airfilter



Another shot down by the air filter



This is the view from the front of the car with the hood up.

 

Often people cut off the top of the air filter top to allow more air to get into it. If this is the case, you should install a front hood gasket to keep water out of it when it rains or you wash the car. Hopefully if this is the modification, the previous owner installed one.

There is even the air cleaner tie mod, where the top is completely eliminated and plastic wire ties are used to hold the filter element in !

I use a 2002 C5 ZO6 air cleaner top on my 1998 Coupe, it has a lot more air intake area, but no water ingestion worries. Some people then cut out the fog light shrouds to allow more air in, like in the ZO6. This does result in a dirtier engine compartment though.

 

Gotta love the zip ties on a $40,000 vehicle (new). Looks like a winter project to get this fixed...

 

In a word........wow...

Good luck with your project sir