carsdwl11

I'm working on my uncle's corvette and can't seem to figure out what is wrong. It will start but if it's cold like it has been it will die. This happens several times before it decided to idle on it's own . Once it does manage to idle it will surge and stumble . The car does seem to run better in the upper rpms if yoh can manage to get it there .
There are no check engine lights on and no codes that I can find.

New parts that didn't fix the problem....
Alternator
throttle body
gas pedal
coolant temp sensor

I'm at a loss as what the problem is.

video of car running.

ls777z

Bad gas or fuel delivery problem?
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cadyshac

Vacuum leak?

carsdwl11

It shows that the fuel pressure is right . While on the scanner a test was ran on the injectors and it passed the test .

I cant seem to find a vacuum leak .

The one thing I did notice was that the throttle position was at 14-20% for an idle .

If I can get these videos if I can get them to load

carsdwl11

https://youtu.be/rVgdjKF2uZs

HERE is a video of the car

Rice Boy

I am still new to Corvette engines, but from previous experiences with different makes and models, I would check PCV, IAC, and TPS. I've had similar issues on other makes/models which has been caused by a clogged PCV, a bad IAC gasket, or a bad TPS. A bad distributor, bad spark plug(s), or wires (loose connection or loss of spark) could cause that also. I would also check to make sure the air filter is tightly connected. I'm also leaning towards a vacuum leak like cadyshac suggested. It took me almost 2 months to track down a vacuum leak on my little beater DD. I had decided to go cheap and got a IACV gasket from O'Reilly's. 2 brand new gaskets later, I took a closer look at those gaskets and decided to order a OEM gasket... that did the trick.

ben dover

MAF Dirty?

truckplay

remove the air box and look inside then the air intake tube and check the MASS, get some MASS cleaner,wash it out and let it air dry then reinstall. without a code reader you are only going to be able to guess. MAP, MASS, Cam Sensor (has 2 harnesses) under water pump and front leaf spring.

carsdwl11

It has been on 3 different code readers from small to a friends very capable snap on unit. It doesn't have any codes in it that I can find.

The TPS is in the throttle body which is why I put a new on it . I also changed the gas pedal thinking that there was a communication issue between it and the TPS .... didn't fix it .

The car was running great before it started doing this . They were 2 hours from home when it started acting up .

Thanks for the help and input !

Corvette_Ed

Did you check all of the spark plug wires to make sure they are seated properly at both the coil and the plug?

Dcasole

Did you do a idle throttle relearn ...not that i think that's it ...you need 3 things , Fuel, Air and Spark .... something is wrong with one of them right ? You obviously replaced the most common parts so now u have to dig deeper

I would use the snap on scanner to look at timing as it could be a bad crank sensor ...then look at what the ECM is doing as the rpms climb ....
Same with the injectors.... it only takes one to go wonkey..scan while running , a tech 11 will try to give u it's best guess on air to fuel ratio , does anything look out of range compared to the others . Are you seeing any missfires ?
And as someone said check the MAF

Good luck
Let us know what you find
Dave

buckmeister2

Sounds like an air or fuel problem.

Have you carefully checked out the MAF sensor? It can do exactly what you are getting, and costs zero to clean. Sounds like you are pretty mechanically-inclined, so you may have already done this.

carsdwl11

I didn't do a relearn on the throttle body when I installed it . I was told that there would be no need to do so . I haven't cleaned the MAF sensor but I will tomorrow and see if this changes anything.

I feel like its a fuel / air problem that I'm simply missing .

THANKS FOR ALL THE HELP ! I will let you know what I find.

carsdwl11

Ok I was just informed that he changed to a new MAF sensor and nothing changed .

warren s

So strange that its running that bad and not setting any codes, seems like its missing on a number of cylinders from what the exhaust sounds like.
Do you have a hand held laser / infer-red type thermometer ? I would check to see if the exhaust manifold is the same temperature near each cylinder.

Pull a plug or 2 and see how they look.

lowflyer

I really don't like throwing parts at a problem to see if it helps. As you have seen, it gets expensive very quickly.
Get a scanner, or take the vehicle to someone who does and look at the Fuel Trim numbers and the B1S1 and B2S1 O2 sensor numbers. These are the Air and Fuel part of the triangle (rotation being the last leg.)
This will tell you if you have a Air/Fuel problem or a mechanical problem.
Fuel trim numbers should be between -10 and +10.
A high Negative number means the computer is limiting fuel, while a positive number means its adding extra fuel. Trying to work itself toward zero.
Also, look for IAC step numbers to see if it is trying to keep the engine running. If the number is high, its running out of air.
Let us know what you find and good luck.

TraceZ

Very strange. This was my first thought as well. Use an IR thermometer on the exhaust manifolds.

Also, get a spark checker and check each cylinder for spark.

Is there any odd odor to the exhaust? raw fuel?

FatsWaller

Some water got into the gas tank, or it was filled it up with contaminated gas just before the symptoms started?

Ahrmike

def sounds like a cylinder is not firing. is your knock sensor going off at all? If so, on what cylinder? that'll narrow it down. What I would do is pull all the plugs, check to see if any of them smell of unburnt fuel. I see one ignition coil is changed... is the plug wire properly seated? I would also try spraying starter fluid into the air intake (postmaf) If it idles properly, one of your injectors is screwy.

msledge50

Is it getting enough fuel. Has the fuel filter ever been change and check the fuel pump