"Hey all, I'm new here, just so you know.
I just bought a 1984 corvette with the crossfire injection and it idles very ruff and is running extremely rich. I would really love to drive her.....any ideas?"



Yes there is if they were disconnected while the engine was running, In this case the ECM has to reset the IAC with the car running at 35 MPH or more.

The IAC valve effects only the Idle characteristics of the vehicle. If its open fully, too much air will be allowed and the idle speed will be high. If it's stuck closed too little air will be allowed and the Idle will be low. If stuck part way the idle will be rough AND will not respond to engine load changes.

I'm looking for the actual measurement of the length of the plunger, as soon as I find it I will post it. I am only trying to help this guy and short quick responses I'm sure are not helping him properly set the TBI's.

I will say that mine ran terrible with pronounced hesitation until I pulled the IAC's and cleaned them, and guess what, after 3,000 miles I pulled them and they were very black. The car was still running good and idling ok but I cleaned them anyway (10 minutes). I could notice a difference again in how well the car Idled and ZERO hesitation.

Why not try it, it can't hurt anything, I could have taken the TBI's off for a rebuild but I did not have to (this time).

Just be sure to NOT disconnect them while the key is turned on.

Adjusting the TBS may also be necessary for throttle response and good idle. Again another easy thing to do.


Hope this helps, getting a Factory Service Manual is a must, it saved me a ton of money so far

 

That line feeds the duct valves in the cabin and the vacuum reservoir which is the ball in front of the vehicle on the drivers side near the headlight. Make sure the vacuum line is good to both locations. The duct valve line follows the firewall and enters the cabin by the heater core. It is a hardline and has a tendency to break - at least mine broke and I chased down the vacuum leak for over a week.

 

[QUOTE=elkabong;1560207195]That line feeds the duct valves in the cabin and the vacuum reservoir which is the ball in front of the vehicle on the drivers side near the headlight. Make sure the vacuum line is good to both locations. The duct valve line follows the firewall and enters the cabin by the heater core. It is a hardline and has a tendency to break - at least mine broke and I chased down the vacuum leak for over a week

 

Hey guys, just an update for you. I removed and cleaned the IAC's and changed a couple cracked vacume lines and she runs alot better. Still a little ruff(but not bad) on idle and maybe a little rich but WAYYYYY better than before. I can at least take her for a drive!
Thanks for all the help, it means alot. I have service manuals coming from a member here so that will help me tons as well. Lots of great people here!
Thanks again, Tim

 

Our pleasure! That is what we are all hear for!

Take care, enjoy the ride!

 

Check the intake lid bolts like CFI recommended. That's usually the culprit of a vacuum leak. May need a gasket. Also, check out the PCV. Those stems crack on the T causing a BIG leak. If that motor is idling up and down, there's a leak somewhere.

 

Welcome to the fold. You're gonna enjoy that first Corvette more than you can imagine.

Glad to hear it's running better, and you can at least drive it. Here's my take on owning an 84 after 10 years now.

1. Get the factory service manual like others have said. It will save you a ton of money and aggravation along the way. If you have the FSM and do your own work, your 84 can be kept running reliably for decades for a reasonable amount of money. If you have to send it to a shop every time it hiccups, it will bankrupt you. Plus you get the satisfaction of fixing whatever ails her. Just remember to troubleshoot as opposed to throwing parts at it.

2. Don't listen to the folks that badmouth the 84's. For those of us old enough to remember, the 84 was a major milestone in the evolution of the Corvette, and in it's time, could compete with nearly anything made on the entire planet. It received many accolades, including the Motor Trend Car Of The Year award. Yes, it's slow by today's standards, but so is everything else that was sold 23 years ago. It can be made as fast as you want it to be, or can be enjoyed exactly for what it was and is.

3. If in doubt, ask. The members here have encountered every possible issue that could arise on these cars, and we've developed a few tricks along the way to fix stuff that might otherwise be expensive or impossible to do "by the book". Here's an example from yours truly.

http://forums.corvetteforum.com/show....php?t=1569397

4. Don't be afraid to drive it, and drive it hard. That's what they were built for. The C4 Corvette is built like a tank, and is very forgiving. Sure, things will break from time to time, but that's part of the fun of owning one. I maintain my C4 very well, am meticulous in it's appearance, and beat it like a stepchild every chance I get. Great fun.

As for your rough idle, keep plugging away at it. Replace every rubber vacuum line you can find, and then throw a vacuum gauge on it. Post how many inches of vacuum you have. I had a similar issue at one point that turned out to be the HVAC controller....was causing a big vacuum leak.

Have fun.

 

Welcome and good luck. The color of your car is a real eye catcher. I also had a high/rough idle with my 84 and replaced all the vacuum lines and plastic T connectors. I pulled the IAC's and cleanded them nicely and the idle has been fine for close to 3 years now. 169,000 miles. I gave her a bath and took her to the Hot Rods and Harley event today.
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Thanks. Your car looks like a real sweetheart.
Yeah I'm still working on getting it running better but I love it.

 

Just be patient. 3 years ago I didn't know the first thing about a Corvette, just knew I wanted one.

There is a wealth of knowledge here on the forum. Pick up the Helms, it's worth its weight in gold. Keep us posted.

 

Will do.....thanks a bunch.

 

 

Man, I love the color. That's what mine used to look like. At the moment she's a bit more undressed:

 

What exactly are you doing to your car?

 

looks like mine in the current state... just got the new motor in the day my truck took a major crap. So the transmission money went to the down payment of the mazda speed 6..... 4 banger with a turbo, not quite a vette, but still impressive with 274 hp..

 

"Bump"...Did you ever find the rest of the cause of your rough idle? I saw that you had 143k on the motor and I'm willing to put money on it that one of the causes still left is your TB shafts are leaking to atmosphere or a vacuum leak.

Generally, the TB shafts will leak at around 50k, I have seen them leak as soon as 29k so far, there is no rhyme or reason when they will start to leak and generally the rear TB is the worse of the two. If the shaft linakage moves at all they are bad and need to be bushed. The Crossfire Injection Vault Forum has more info on that. You won't beleive te difference that bushed TBs will make, honest.

Did you also check the top plates to se if they were tight? Check them...

 

Yeah....I installed new gaskets on the TB's, tightened all the bolts ect. Changed vacume lines and did a full tune up. Verdict?..........it runs like a champ! I could'nt ask for more at this point!
Thanks for the interest.

 

Outstanding! I'm cleaning my IACs tonight!

 

Great! Glad you got her fixed up and running.

 

Thanks Bro! By the way.....what do ya think of the new wheels??