Alright guys so I have a little problem with my 98 coupe, the other day my car was running perfectly fine, normal idle and no codes. I took off my ls1 intake and swapped on an ls6 I take ALSO with a ported stock throttle body and ported/de screened MAF done by Potz.

Ok so after I swapped everything on, I made sure all bolts were tightened and had all vacuum lines hooked back up, also checked all my Injectors and fuel rail and it was all on tight.

So I cranked her on and she idles pretty smooth in park, now I know our vettes are pretty known to have a little rough idle to begin with so I'm used to that. I throw her in reverse and now the car starts to get a little shaky. Now when I put her in drive and hold the brake, she idles around 500-600 and it feels alot more violent, not too crazy but defiantly noticed and now it's uncomfortable. To the point to where I'd rather throw it in neutral at a stop light then have it in drive.

Another factor in this problem is that my check engine light is on and when I drive it from 30+MPH the check engine light starts to blink and stops blinking when I get back down under 30 MPH.

I've driven the car like this for a bout 25 miles, most highway, and all gauges are operating normal, all temps are where they should be too.

My input is that I need a tune.... I'm thinking that the car is bringing in alot of extra air into the engine it's not used to it, I also have a vararam installed.

What do y'all think?

 

Anyone?

 

Blinking check engine light indicates a misfire. Plugs or wires are the most common cause.

 

Pull your codes and post them here

 

You have fallen into a trap that many of us have also fallen into.

You have most likely altered the TUNE of the engine.

Anytime you mess with the AIR FLOW through the engine you can expect some kind of small issues.

You should have left the screen in the MAF. The MAF is calibrated (thru the PCM ) to meter air with the screen in place. When you remove the screen, it no longer properly calibrated.

The LS6 style intake and the new ported TB will mainly change the mid to upper range engine charestics/power.

The ported TB can sometimes effect idle depending on how it was ported.

RECOMMENDATION: Find someone with tuning software and DATA LOG the PCM and see what your Long Term Fuel Trims are doing. They should be close to zero or slightly negative

Spray some brake parts cleaner around the Maifold, Air bridge, TB and intake accordion tube and see if it changes the idle speed/quality. If it does,that indicates you have an unmetered air leak.

After you make sure that you didnt do anything wrong,,, YES,, you will need a tune. Also consider doing any other MODS that you want to add before you actually tune it.

BC

 

@bill ok ill try that and see if it helps

And as far as the misfiring, I'm kinda stumped on that because I don't see how it could be since right before the swap it wasn't misfiring at all or anything. I don't see how within that time a misfiring issue could pop up after a manifold swap.

 

The tune could be messed up because of the changes but shouldn't be the cause of a misfire. Double check the the plugs and wires, otherwise do as Bill C. says.

 

did you check the brake booster and make sure it's hooked back up? did you replace the gaskets and make sure you have no vacuum leaks?

even if the tune is off it shouldn't be misfiring at idle unless you forgot to plug something back in and or have a vacuum leak.

 

Too much air, you'd be getting lean codes. Sitting at idle or just going into gear and your having issues-You have a vacuum leak somewhere. Start spraying around with carb cleaner see it you can get the idle speed to change.

 

Ok guys thanks for all the help ill check it out today!

 

***** Alright so I went out and bought brake and throttle body cleaner. I sprayed the brake cleaner around the manifold to see if there was any leaks and all seems good.

I then sprayed some TB cleaner into the air bridge and my car started to hesitate.

 

Its either TOO LOOSE or TOO TIGHT.

If the clamps are TOO TIGHT, they cam collapse the bridge and allow air in the collapsed area. Use an inspection mirror and examine all the joints...

Bill

 

If you sprayed it into the air bridge that is what I would expect. I would check the wires and plugs again for good connection and see if you have any fireworks under the hood at night. If all is good there I would suspect the work you had done on the maf to be the problem. How do you port a maf anyway? Do you have a stock one you can swap to check? Also PULL THE CODES.

 

Alright everyone, BIG UPDATE***

I replaced all my spark plugs with NGK-TR55's and also replaced my wires with eBay 10.5 mm wires.

After replacing all that the car ran just a tad better. I figured I came to the conclusion that it just needs a tune. Oh and btw the check in light was still on and flashing above 40MPH.

Ok so about 5 days later I decide to drive my Vette to Houston to run an errand. Which is today. That's about 50 highway miles. I'm driving her and it's running okay not to worried about anything so I go ahead and step on it a bit. I go up to 100 a couple of times and the cruise around 60-70. I get my destination in Houston turn the car off, take care of my business and come back to my car.

I turn my car on and something just feels different. For some weird reason my car is idling perfect!!! Not shaking at all not missing a bit, and she's purring like a kitten I just drove home from Houston and the check engine light has been off the whole time!

Idk what happened while driving today but it made my car run back to perfect she feels 100x better!

Can anyone explain what happened? Lol

 

If I had to guess, the car finally get through all of the adjustments needed to idle properly. The car's computer will adjust to changes in air volume on its own, it just takes time. There is a procedure that is documented on the forums on how to force the issue but it might take 50-75 driven miles to get it all sorted out.

 

that only adjusts closed loop to a point. open loop is fixed via the tune

that means warm up and WOT ignore the o2 sensors and are fixed to whatever timing and fuel are on the tables