Sephiroth1991

like 84 corvette starts up fine but if my foot ain't holding down on the gas it will idle real low like 200 to 300 rpm then die in a second. But when I tap the gas it gets it idling fine. I did take the locking collar off the injectors last Sunday but put it back on and the problem didn't start until then can anybody help

s carter

Have you looked at the IAC system and made sure that the piston is moving and the passage ports are clear.

Bad IAC no base idle control

When you look at the Injectors are they both Spraying ?

ToniJ1960

sorry about sidetracking a bit but what do you mean by locking collars? Asking because I have an 84 also

Bfenty

Also, check your minimum idle set screw, it's on the side of the throttle body where the linkage is, you might just have to tighten it down a little to get the idle up.

Next thing to look at is your TPS (Throttle Position Sensor). It's on the other side of the throttle body from the linkage. As the name implies, it tells the computer where the throttle is currently at, which determines how much fuel it needs to send to the cylinders. To fine-tune it you need a voltmeter. Rotate it until it reads 0.54 V at idle between the top two wires coming from the TPS.

Those are what I would check first-let us know what your results are.

billschroeder5842

YIKES! Please dont't mess with the idle screw as it is welded and set from the factory. I had an 82 with the XFire and they are the same engines.

Here is my guesses:
Your car sounds like it suffers from low fuel pressure as you tap the gas and it pops up briefly. the XFire engine is notorious for low fuel pressure problems. Your two culprits will be your fuel filter or your fuel pump or both. Check your fuel pressure and you will need at least 11 to work at a minimum.

At some point consider upgrading to a 85-89 fuel pump. A direct, bolt on replacement and will give you 15psi. Your XFire will be a different car.

Hot Rod Roy

The fuel pressure is controlled by the regulator, which is in the rear throttle body. Changing the fuel pump won't change the fuel pressure. There's no need to change the fuel pump unless you have a problem! Increasing the fuel pressure will cause the ECM to reduce the injector pulse width to keep the fuel/air ratio in balance.

Bfenty

hmmm...I have an '85 and the idle set screw isn't welded at all. maybe it's different in later years?

billschroeder5842

IF your regulator has enough pressure to begin with, it will keep it a stead flow to your engine. The problem is that aging fuel systems fall beneath the FPR threshold. A new fuel pump, will provide slightly more pressure than necessary ensuring that minimum standards are always met.

Buccaneer

Your 85 vette does not have TBIs like the 82 and 84 vettes, it is fuel injected.

I have no idea what locking collars are on the injectors? Please explain or post pic. Are you by chance talking about the injector filter baskets?

There are a few things to check, but if you're not familiar with CFI, start reading up on it before messing with the TBs or you can really mess them up. Get a 84 GM Shop Manual for sure since it explains a lot on how to maintain your CF. I think the 84 manual is better overall in the troubleshooting area than the 82 manual.

Now to the "possible" problem(s)...

1. Your TBs sound like they may be out of balance and the shaft ware may be bad causing the balance to be off. If the shaft ware is extreme enough, no matter how perfect the balance is any time you hit the gas, it will go out of balance, hence an idle change. IMO...(DON'T MESS WITH THE BALANCE UNTIL YOU UNDERSTAND HOW THE SYSTEM WORKS) If everything is working properly, your idle should be approximately 1,200-1,300rpm cold and drop down to your warm idle about 450-500rpm steady on a stock motor.

2. The IACs may need cleaning which will also contribute to an idle issue since the IACs are a controlled vacuum leak. DO NOT pour any cleaner down the pintal end with the spring, you will more than likely ruin the IAC. Just clean the pintal end with cleaner and rag to get any carbon/dirt off.

3. If you are NOT setting a CEL, the CTS sensor should be OK, but your TPS sensor may be off enough to NOT set a CEL. TPS sensor setting is .525MV. This is set so that the ECM knows what the angle of the TB blade is at idle. Also, if you adjust the balance in any way, you MUST readjust the TPS sensor to the correct value mentioned.

4. Where is your fuel pressure? CFI motors are rather sensitive to FP. Set it at 13psi (rear TB) and you'll be fine as long as the pump can support that volume.

I hope this helps you out.

billschroeder5842

Buccanner- Glad to see you in C4 land!

I really appreciated your help when I had my '82 XFire!

Buccaneer

Thanks I stop in from time-to-time to see what's going on in here. Tom usually has this year covered though.

Hot Rod Roy

C'mon, Tom, you know your stuff. As they say, "The devil is in the details". Please get your facts straight.

What do you think the "I" stands for in TBI?

That's .525 VOLTS, not millivolts. Anything between .50 and .55 volts is fine.

Thanks for you usually good suggestions!

Buccaneer

OK, you got me on the TPS... Volts is what I meant. Was that AC or DC?

Not sure about the TBI though. There is a difference between true TBI and fuel injected, as in the 85 having eight fuel injectors and a TB that only does air flow vs. two TB injectors, but I see your point. Again, I knew what I was talking about.

Hot Rod Roy

The '85 & up TPI has two injector driver circuits in the ECM, with each circuit firing four injectors at the same time. The '82/'84 TBI also has two injector driver circuits for the two injectors. So the TPI is firing its fuel injectors into ports with CLOSED intake valves most of the time! Sounds like a screwy idea to me!! And it sure is handy to be able to see what's happening with your fuel injectors in the '82/'84 TBI system! Try that on your TPI!



It's all good! Just havin' some fun with you!

Bfenty

My apologies-I thought '84 and '85 were more similar than that. Just trying to help!

ToniJ1960

Were all learning things here and there its one of the things I enjoy here.

So many times a post gets made about "c4" corvettes or a statement is made referring to "c4's" and I think how misleading it can be without the regard of what year c4. Theres probably more differences than most think and its too easy to add to that misconception by the simple process of oversight. I wish I knew a lot more about all the differences but Im probably going to be around for a while still learning as long as its in my cards.

James84vette

I noticed a difference when I changed my pump last summer and I didn't touch anything else. Mine was acting up and the idle was going up and down, I'd step on the gas and then the idle would stay high. I took the pump out yesterday and found the sock/strainer had come off and the pump was clogged.


I'd suggest buying an '85 pump, new sock/strainer and change it. Easy swap and when your ready adjust the FPR.