Dechaotic

Hello, I own a 1986 Pontiac Firebird - V8 305

When I first bought my car at the begining of the year I had very minor problems. I had to replace the wires to my fan, since the past owner burnt it out. Then soon after, my car started to sound like it was revving high whenever I was in park and idleing. After I would shut off my car, my engine would start to shake continously for a minute or so and then finally would shut off. I soon found out that my engine was dieseling. Which is my main concern. Soon after the dieseling happened a friend of mine noticed their was a leak and we found out that my waterpump was shot. So, we changed the waterpump and hose to my radiator and then the dieseling actually completely stopped. For a long time my car drove perfect and fine (maybe for a month or so, it's a daily driver to school and work). After I thought everything was ok, I just recently heard her revving high again when I was in idle and what I was afraid would happen, did happen. And this time when I shut her off she diesled for a minute straight and it's no fun when someones looking at your car thinking it's gonna explode or something.

I had a friend look at my problem and we believe it's a potential carb problem. To make matters worse, the other day when I turned her over, she wasn't gettin any spark, just gas and it seems that my choke is staying shut so she isn't getting any air to start up. I took apart my carb and basically sprayed a lot of carb cleaner where necessary, but it didn't do much.

I was hoping someone here could help me out or figure out what problem my car may have. My main concern is the diesling and the high revvs when in idle. It definitly seems to be a carb problem, but I'm not sure what I can do to fix her up. I appreciate any help and thank you for reading.

- Roger

Sonix

iTrader: (1)

Is the choke wire on? Loose?
What's your hot idle speed? Cold?

If it's revving too high (throttle stuck open, due to choke, or idle speed->ie stuck throttle shaft) then dieseling is pretty normal. That or too much timing.

Check your plugs, change if needed.
Then tinker with your choke. Make sure the wire is on. Make sure it's not sticking. I'd guess it's just got some junk in there causing it to hang open every now and then.

lukn4trbl

Also try looking for cracked/loose hoses causing vacuum leaks.

The idle speed (closed throttle angle) can cause dieseling if the transfer
slots are exposed too much. Back off the idle screw if that's the case.

Sonix

iTrader: (1)

Yes, I almost forgot, cracked hoses are a big one. They can cause the intermittent high idle/dieseling that will drive you nuts. You can buy 5-10' of 7/32" hose or whatever size it is, and just replace most of it. and some 3/8" for the brake booster and PCV.

campin1983

iTrader: (4)

I can't help but remember a car that was dieseling and we couldn't shut it off. After forcing the fuel pump off, and even removing fuel lines, it still didn't shut down. To our horror, we figured out that the motor was leaking oil so bad internally that it was burning its own oil to keep going. Unlikely to be the problem, I'd imagine this was an extreme and very rare case (not to mention that motor never fired up again once we got it stopped), but it made me think of that.

dbusicchia

I had the same problem with my 86 camaro. I found a broken vacuume hose on the back of the intake manifold which had plenty of slack cut back the brocken part and it hasn't diesled since. The high idle problem I fixed with the idle screw, it was idleing at about 1500 RPMs now its about 750-800 RPMs. Hope this helps

Dechaotic

Thanks to everyone for the help and suggestions. I'm gonna definitely look everything over. I took another look at her yesterday and I did infact notice smoking going on in the back of the manifold, I'm guessing that is a leak and I will probably tend to fix that asap. I also was able to get her started, but she was bogging and it seemed like I was stuck in lower gears when I was actually in drive, plus she was still in high revvs. I'll probably need to look into rebuilding my carb (a quadrajet rochester). I also noticed that my catalytic converter is pretty damn shot which can also explain the bogging when driving. When I started her up for a few minutes the cat was already so hot that the metal was actually turning red almost as if it was an oven. I'm thinking about gutting the cat for now and get a new one when it comes time for inspection (I'm living on low-budget). Well thanks again for the help and if there's anything else to add please do, I'm pretty sure there's multiple problems going on with her right now and I'm basically open to any help.

- Roger

dbusicchia

my 86 Z28 is diesling again. no broken vacuum lines, carb has been adjusted, but intake manifold is leaking could it be burning excess oil?

Sonix

iTrader: (1)

An intake manifold leak IS a vacuum leak.
And yes, it would be burning some excess oil at the same time. Get fixin man!