BSenzina

HI all....I am new here and jsut got my 1st vette a couple of months ago. It ran rough so i got it a tune-up last week.....It runs MUCH better but it has a stumble at idle and sometimes idles a bit rough. Also, when its hot, its sometimes hard to start, acting like the choke is stuck or its flooded. I know there is no choke. Any ideas?

solaris_vii

i dont have an 84 but i do have an 82 and well, same engine. i had a similar problem with the hard to start and had i guess a "searching" idle it would rev up and down between 500 rpm to 1500 rpm, got a lot of tips on vacuum leak egr etc but in the end it was a failing fuel pump. might wanna check your fuel pump and fuel filter, pretty easy to access on the c4 (well fuel pump anyways) and arent too expensive. a delco one is like 70 i think or you can get the racetronix/walboro package (which i recommend, no wire splicing) for a little over a hundred. even if its not you ultimate problem its something good to replace on a car that has sat for a while. i know ive been stranded by a fuel pump failing. good luck tracking it down!

jhammons01

This may help

http://www.corvettefever.com/techart...ing/index.html

mundo

I had an '84 and it ran strong but not until I did a few things.

1. '84 CFI sounds real rough when starting cold. The air intakes in the hood connect to the air filter housing. One of the air intakes keeps this 'flap' closed when the engine is cold causing a very rough idle. I believe its spring loaded 'open' with a vacuum actuator keeping it close on cold start. I think I removed the vacuum line to it causing both air flaps to stay open. This eliminated rough idle at cold startup.

2. Get '85+ fuel pump. '84 FP is a weak sister. The '85 FP will eliminate hesitation providing fuel filter is clean and injectors are OK.

3. Add Ram air intake. Cut a hole in the air box with a moto drill the size of the air intake in the hood. Use good house hold weather stripping around the hole for sealing. Helps breathing with cold air at WOT. You'll see in one of my engine pictures what I'm talking about.
http://forums.corvetteforum.com/c4-t...king-84-a.html

4. Get a Renegade. Much improved breathing. Increase your red line beyond 4800 to about 5800.

5. Get 2" TBs. Won't fuel starve at high rpm.

6. Get higher compression heads.

It'll run like a bat out of hell and go kick some C5 automatics butt.

CRUZN C4

Sounds like a fuel pump issue. Chances are it could be yhe original one or one that was replaced a long while ago' I had an 84 that had similar issues and the pump finally died. I replaced it with an 85 pump and solved all my issues. Hope this helps.

Lemme

Can't see what you mean from those pictures. Where is the air box on an 84?

ex-x-fire

Check the coolant temp sensor, its located in the front of the intake near the air pump. The 84s had an early style sensor that can be troublesome, get a later style sensor & pigtail connector.
You can try wiggling the sensor to see if it acts up.

mundo

In the picture, in front of the fan there is the radiator housing. Directly front of that is the air box. Notice the square hole in the air box. Also, notice the the hood meets the air box and the hole in the hood used to draw air. When the hood closes the the hole in the hood is directly over the hole in the air box drawing cold air. Normally '84s don't have that hole in the air box cutting off the air when the hood is closed. Really noticeable at wide open throttle (WOT).

Lemme

I thought that was it. But why did they design an airbox where the air can't get through to the intake?

mcm95403

Why oh why do OEM's do so many things like that!?!?!? I would bet that the increased intake noise from opening that up was a problem, so they left it for us to do if we wanted to. Noise standards can be a funky thing.

To the OP, I'd take a look at a worn throttle position sensor. It could cause this sort of problem too.

Buccaneer

Check your fuel pressure in-between the TBs. CFI is rather sensitive to fuel pressure. Set it for at least 13-14psi and that should be fine. Next, what is the TPS set to? Set it at .525v or as close to that as possible. Set it with...Key ON, engine OFF. If these two don't help, start looking for vacuum leaks, check that top plate. Good luck.

mundo

Rumor has it in '83 GM had the TPI working with much better performance than the CFI. The rumor is they purposely did things to reduce CFI performance until TPI was production ready. When you take the CFI intake manifold off you'll see the intake runners are half the size on the manifold side than the head side. They plugged it up on purpose. Maybe TPI was less expensive in production. Many times the automotive engineers were told what to do by management to save a dime.

Bottom line - make a CFI breath and not starved for fuel or air and it gets impressive. Renegade has replaced X-Ram. With a Renegade intake manifold and 2" TBs and some of the tips I mentioned your L83 CFI will rock. The guy who was selling X-Ram was getting about 450 hp from an '84 CFI with a stroked 383.

Lemme

I liked that air box mod so much I thought I'd have one myself

PLRX

Rumor? Where the info came from?

mundo

Just something I heard at a Corvette show.

BSenzina

Im a HUGE CHICKEN ! ! What did you cut this with??? Is there some sort of an outline on this spot you followed, or what are the measurements??? OMG my stomach gets butterflys just thinking about doing this ! !

Lemme

I just did it by eye. Otherwise get some cardboard and cut out a template, draw around the cardboard on the top of the airbox with a marker and then drill holes in the corners. Then get out your jigsaw / hacksaw and cut. It is fibreglass so it cuts easily. Don't breathe the dust. The weatherstrip is 25mm wide by 19mm deep. Total cost less than $5.

If all you have is a drill then get a small bit and drill a hundred little holes around the perimeter and then remove the rectangle cut out and then smooth with a file. That is the way I did it.

BSenzina

OK......Since this surgury has been completed....has the engine noise increase??? Still glad you did it???

Lemme

I can't say I can hear any particular noise increase. Not at idle anyway. At WOT it may start to become audible but I wouldn't think it would be much.

No regrets. When my new renegade intake manifold arrives I want to let as much air through it as possible.

mcm95403